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Air-conditioning systems

Always flush the air-conditioning system to remove any contaminates and replace any parts that cannot be flushed. It is also a good practice to use inline suction filters to help catch any foreign material.

When working with either PAG or Ester oils always be sure to keep the container capped when you’re not using it. The chemical makeup of these types of oils will absorb moisture and can create a problem in the air-conditioning system later.

Air-conditioning systems can be contaminated with metal particles from the normal wear of the compressor and tiny amounts of water moisture. Contamination can cause a system to fail. Protection against contamination is provided by the filter screen on the Expansion Tube and the desiccant in the bottom of the dryer or accumulator. Other forms of contamination may be the wrong kind of oil, wrong kind of liquid charge or other material that will interfere with the cooling system. Almost 100% of moisture is normally removed from the system when it is evacuated prior to installing (R12 or R134a), but flushing the entire system will be the only way to remove any particles.

There are different types of checks that can be done on the air-conditioning system. Most checks include the following. Visual inspection of the compressor and lines for signs of air-conditioner oil leakage, noise inspection, belt inspection, testing the low and high side pressures for the proper amount of refrigerant, air-conditioner output vent temperature test, inspecting and cleaning drain tube, inspection and confirmation of proper fan operation.

Even if someone has told you what is wrong with an air-conditioning system always perform a visual inspection prior to connecting a gauge set. There is any chance that someone has used the wrong refrigerant or failed to evacuate the system properly! Then you need to fully recover and then recharge with correct refrigerant to avoid personal injury due to unpredictable high pressures developing the system.

Stabilising the air-conditioning system

Before making any evaluation of a system it is important to “stabilise” it. Once the manifold gauge set has been installed and the manifold gauge contains no air, the system is ready for testing.

The system should be run for a few minutes as described below, in order to stabilise the manifold gauges.

  • Check that all gauge hoses and tools are away from moving engine parts and electrical terminals.
  • Switch on the air-conditioner to its coldest setting and full “recirculation”. Set the fan to its maximum speed.
  • Open all doors and windows to allow the interior of the vehicle to quickly reach ambient temperature.
  • Set the electric thermometer into the outlet louvers.
  • Place the portable electric fan in front of the radiator and condenser.
  • Operate the system like this for 5-10 minutes before taking readings.

It is recommended to install liquid line filters and suction screens when previous system failure was the result of compressor, accumulator, or receiver drier failure. Additionally, flushing the system with refrigerant is recommended.

Checking for Leaks

Once the gauges have been installed and the system stabilised, follow these steps:

  1. Switch off the engine.
  2. Carefully, check each joint in the system for any witness of oil.
  3. If a fluorescing dye has been used in the system you may shine a UV light on each joint and look for the evidence of oil, as it will shine brightly.
  4. If no dye has been used, then use an electronic leak detector.
    • Set the detector in accordance with the manufacturer’s directions.
    • Move the wand about ¼ to ½ inch away from the joint.
    • If a leak is detected the alarm will sound.

Fixing a Leaking Joint

Evacuate the system using an approved refrigerant recovery unit.

Once the system refrigerant has been removed proceed as shown below.

  1. Use two wrenches to undo the joint. One wrench is a backup to avoid twisting the fitting and causing further damage.
  2. Separate the joint and remove the O ring and discard.
  3. Carefully wipe both parts of the joint.
  4. Take the new O ring and wipe it and both parts of the joint with compressor oil.
  5. Reassemble and tighten the finger. Take the two wrenches and tighten carefully – be sure to not over-tighter. Larger joints can stand a greater torque. Recharge the system and retest.

Improving Air-conditioning System Performance


Poor system performance can often be improved by cleaning the condenser. The purpose of the condenser is to reject the heat from the interior of the air-conditioned space. It is constructed of tubes and fins brazed together in a matrix. Small air passages on the outside allow air to flow through the condenser, cooling it down and removing the heat. It is important to keep these airways clean.

Normally, condensers are mounted in front of the radiator and directly behind the vehicle front grill.

  1. If possible remove the vehicle grill and top cap under the hood. These are normally held in place with plastic “pop out” clips.
  2. Compressed air may be used to blow through the condenser in a reverse direction by placing the air line between the radiator and condenser. A long tube attached to an air gun may be useful. Take care to avoid touching either the radiator or the condenser. The cooling fins are delicate.
  3. Brush the air inlet side to remove dead bugs and grass with a bristle brush. Do not use a wire brush. Brush in the direction of the fins.


Be aware that there are companies in the market today selling products that promise to improve the performance of your aging system by using their magic additives. DO NOT BE FOOLED! There are no quick solutions and no SILVER BULLETS!!!

Adverts show lower cooling vent temperatures after using these products. These are sold at all major auto parts stores and come in the form of a nicely packaged cylinder of refrigerant with names like ”extra cold, super freezer” etc. To the refrigerant is added a chemical, which claims to seal all leaks in the system. Many vehicle owners have found how expensive this additive really is. When the chemical is put into the system it migrates to all leaky areas and does in fact seal them. The major problem is that it seals the moving parts of the compressor. This causes the clutch to fail and the system to become inoperative.

Fixing the problem is not cheap. The majority of shops will either not work on a vehicle they know to be so polluted or will recommend complete system replacement. No vehicle or compressor manufacturers condone the use of these performance enhancers. Use only the products recommended by your accredited service shop and vehicle manufacture.

Typically a good working system will have cooling vent temperatures 2-30 degrees lower than ambient. Get to know what the sound and feel of your air-conditioner is like when blowing on maximum. If the temperature is low but the air flow is slow when set on maximum, it could be that your cabin air filter is blocked. Locate and replace.


Topping off means adding more refrigerant to an air-conditioning system when low performance is suspected to be caused by a small persistent leak.

Of course it works (for a short while) and the customer happily goes on his way. There are several problems which you should be aware of though:

  1. If the refrigerant has leaked out, so has the oil…
  2. You just added to the Earths “green-house” warming affect by R134a pollution. Loss of lubricant will hasten the failure of the compressor.

The correct procedure is to find and repair the leak and properly charge the system with the correct amount of refrigerant and oil!

Pulling a Vacuum

You have completed your repairs to the air-conditioning system and ensured the correct amount and type of oil has been put in. It is now time to fill the system with refrigerant. But first we must evacuate the system.

We evacuate the system to remove the two major pollutants found in recovered refrigerant: water and air.

Connect the vacuum pump to the yellow manifold gauge hose having first connected the red hose to the high side service port and the blue hose to the low side service port. Switch on the vacuum pump and open the manifold gauge valves and watch the pressure drop. The needle should reach -30 on the suction side if all is well. After a minimum of 45 minutes evacuation shut both manifold gauge valves and leave them closed for 15 minutes to see if the needle moves. If it moves you’ve likely got a leak and you’ll need to fix it before progressing. If you passed the test you are now ready to charge with refrigerant.

5 steps to repair an air-conditioning system

Step 1: Learn the system

A vehicle’s air conditioning system works by creating a super-cold element and then circulating air over it and into the vehicle cabin to remove the hot air from the vehicle cabin. The circulation is the product of a fan. Creating the cooling element is the difficult part.

This is accomplished by transitioning an air-conditioning refrigerant (typically R-134a) through a series of gaseous and liquid states that turn it ice cold.

The refrigerant is stored in the air-conditioning system as a gas. When you flip the air-conditioning system on, this gas is compressed, causing it to liquefy. The liquefied refrigerant then flows through a high-pressure line to a radiator-like component that condenses it and removes any heat.

The cold liquid flows through a valve into an evaporation unit where it becomes a gas again. The cold gas turns this unit into a cooling element that air can be forced over to produce air conditioning.

The refrigerant warms as it is used here. To keep the cold air flowing, the refrigerant is sent back to the beginning of the air-conditioning system where it is compressed again and transitions once more through the air conditioning cycle.

Step 2: Know the parts

Most air-conditioning systems consist of five basic components, along with sensors and refrigeration lines. The components are:

Compressor: As its name suggests, the compressor pressurises the refrigerant and is the first and last stop in the air conditioning process. An engine belt powers the compressor. An electrically operated clutch turns the compressor on and off as the demand for cold air increases.

Condenser: The condenser functions like a miniature radiator-cooling (by removing the heat) then liquefying the compressed, hot gaseous refrigerant as it passes through. The condenser is typically located near the vehicle radiator, sometimes directly in front of it. Like the radiator, the condenser sometimes is fitted with a fan.

Thermal Expansion Valve: This valve controls the flow of the liquefied refrigerant, allowing the motorist to determine how cool the air will be when it enters the vehicle cabin.

Evaporator: The evaporator is another kind of radiator, much like the condenser. The evaporator, however, reverses the work performed by the condenser. It “evaporates” the liquid refrigerant, turning it back into a gas that chills the evaporator fins. Air blown past the fins becomes icy-cold and is transferred into the vehicle where it cools the interior. The refrigerant remains in the evaporator until it begins to warm and lose its cooling effect.

Accumulator or Drier (or Receiver Drier): The warm refrigerant makes its way back to the compressor but must pass through one more component -the drier.

Refrigerant can only be returned to the compressor in the form of a gas. Sometimes, however, liquid gets passed along (usually because the gas refrigerant warms and returns to a liquid.) Liquids pose a serious risk to the compressor, where they can cause severe damage. The drier catches and absorbs liquids using a chemical known as a desiccant. Because refrigerant carries dispersed oil to keep the compressor lubricated, the drier also includes a filter to trap any accumulations of oil or other “gunk” that may get passed through the air-conditioning system.

Step 3: Obtain the proper tools

The majority of damaged air-conditioning systems experience some type of leak, which means your techs will use UV dye set to identify where refrigerant is seeping through. Some OEM’s do not allow dying of their systems, so your techs should be making use of three other tools to spot system damage:

  • Electronic refrigerant leak detector: Sometimes a UV dye set won’t reveal a leak. An electronic leak detector can check the entire system in a matter of minutes, including the evaporator.
  • Air-conditioning manifold gauge set: Determining the pressure readings on the low and high sides of an air-conditioning system are essential to troubleshooting problems, making an air-conditioning manifold gauge set an absolute necessity. Newer sets include anti-blowback features, but techs should still wear safety glasses.
  •  Flexible inspection mirror: Because air-conditioning components are packed tightly in the engine compartment, locating damaged parts; especially bent lines and damaged evaporators can be difficult. A flexible inspection mirror can fit into these tight areas and help turn up hidden damage. 

Step 4: Difficult diagnoses

Often when air-conditioning systems are damaged in a collision, it is easy to spot to damages. A front-end collision should indicate the possibility of air-conditioning damage. An inspection of the engine bay is the first step in uncovering problems.

Even if the air-conditioning system appears fine, the next step is running the air conditioning and evaluating its performance. From there, a certified air-conditioning tech can perform the necessary diagnostic tests and repairs. Most air-conditioning problems can be traced to broken components or system leaks. Fractured hard lines (aluminium) and flexible (rubber) air-conditioning lines are frequent culprits, as are punctured condensers, since they frequently are located at the front of the vehicle, near the radiator where they are vulnerable to damage in front end collisions.

Some air-conditioning problems can be far more difficult to spot, especially passive refrigerant leaks. There are two types of leaks, active and passive. Active leaks constantly lose refrigerant and thus show up more easily during leak tests. These leaks are typically the result of collision damage to belts and lines that are bent or crimped when nearby engine parts are pushed into them. Engine and other mechanical components sit so close to one another in the engine bay that even a light hit can press them into one another.

Passive leaks are intermittent so they may not show up during a standard evaluation and only appear at times when the vehicle is running. These leaks are the products of damage elsewhere in the air-conditioning system that interfere with the system temperature and pressure and create vibrations. Possible damage includes shaft seal leaks in the compressor or a cracked braze on an evaporator or condenser that is no longer properly supported. In these cases, a UV dye test will be more effective at finding leaks than an electronic test.

Passive leaks can take time to diagnose. Sometimes, they may not be apparent until after a vehicle is returned to the customer. Your shop needs to keep these factors in mind when performing a final quality inspection on the vehicle and if a customer calls later with concerns over the air-conditioning system. In many cases, the latter issue can be avoided by performing a UV dye test on every damaged (or potentially damaged) air-conditioning system and by thoroughly examining the system during a road test.

Step 5: Offering further recommendations

Even if the air-conditioning system isn’t damaged in a collision, that doesn’t mean you should ignore it during a vehicle inspection. Most vehicles on the road today (and well over 90 percent of new vehicles) have air conditioning. Repairing faulty air-conditioning systems and offering maintenance can provide significant revenue.

Consider evaluating the air-conditioning system in every vehicle that visits your shop, especially those older than three years or more with more than 150000kms. Over time, many of these systems need to be recharged to return them to proper functional levels. Air-conditioning systems that aren’t maintained pose significant, and potentially costly, problems for vehicle owners.

Inform your customers of the following:

  • Contaminated or low refrigerant or faulty air-conditioning electrical wiring can ruin a compressor. This by itself is a serious issue, but it also can lead to even larger problems. Damaged compressors can send electrical surges throughout the air-conditioning system and to other parts of a vehicle causing severe damage to both. Even if a vehicle escapes these issues, a faulty compressor can produce other issues, including draining the battery (thereby shortening battery life), reducing fuel efficiency and creating poor idling.
  • A number of air-conditioning problems can be repaired fairly inexpensively. Replacing the refrigerant is affordable as are other necessary services. For example, fluctuating air-conditioning temperatures can be the result of moisture building up in an assembly or hose where the moisture turns to ice and creates a clog. Removing the ice is quick and easy. A weak or aging car battery can cause a number of air-conditioning performance issues that can be remedied with an inexpensive replacement.

Foul odours emanating from the air-conditioning are typically the result of bacteria that build up in the evaporator. A quick evaporator flush will eliminate the problem.

The beautiful new finish and fresh body work you’ve provided can restore a vehicle with a new look that shouldn’t be paired with air-conditioning problems. Collision repairs provide an ideal time to address other vehicle issues. One of the best ways to appreciate the sharp look of a repaired vehicle from the inside is with clean-smelling, fresh, ice-cold air. Motorists and repairers can both agree to that.

Binary Pressure switches

A binary pressure switch is a compressor safety device that has 2 distinct functions. The first function cuts the compressor off if the refrigerant charge is lost or too low to prevent the compressor from running dry and locking up. The second function cuts the compressor off if the head pressure reaches unsafe levels to prevent compressor damage or damage to other components such as a blown hose.


The compressor clutch has been around since shortly after the first air-conditioning systems were installed in vehicles in the late 1930s. While they have certainly undergone many changes over the years, no matter what style of clutch is used on a compressor, they are all designed to perform a similar function: to engage and disengage power to the compressor input shaft.

Poor system performance could be faulty reed valves. A hissing sound from the compressor immediately after shutdown indicates high side to low side pressure leakage. To check this, attach manifold gauges and turn compressor on. Readings showing lower than normal discharge pressures and high suction pressures or a rapid stabilization of gauge readings shortly after shutdown indicate leaking reed valves or head gasket.

When replacing the clutch assembly always make sure to re-install the snap rings properly. Snap rings have two sides, one is flat and the other bevelled. The bevelled side should always go to the outside to ensure proper fit.

Things to do and look for when draining oil from a compressor:

  1. At what ambient was the compressor drained at? Hot = more drained oil, Cold = slow/less oil.
  2. Were the ports/caps removed to prevent a vacuum?
  3. Was the oil drained and measured from the cylinder head as well as the compressor body?
  4. Please remember that depending on the temperature at time of draining that approx. 1/2+ oz will remain in the compressor.
  5. When the compressor was drained was the compressor crank turned or rotated?
  6. How long was the compressor drained?

Checking Compressor Oil Colour and what the colours mean to you:

  1. Black – Air in the system causing carbonation
  2. Brown – Moisture causing copper plating c) Grey or Metal Shavings – bearing and/or piston wear, therefore you must flush the system, replace the Receiver/Drier and evacuate/recharge.
  3. Grey or Metal Shavings – bearing and/or piston wear, therefore you must flush the system, replace the Receiver/Drier and evacuate/recharge.

Clutch slippage is a common cause for clutch and or compressor failure. The heat created when a clutch slips can damage the pulley bearing and weaken the compressor shaft seal. During any service work to the air-conditioning system always check voltage to the clutch coil and air gap between the hub and pulley to prevent slippage.

Did you know?

The most common reason a replacement compressor fails (new or remanufactured) is caused from contaminates from a previously failed compressor.

Some new compressors can leave the factory without an oil charge but checks and balances in most manufacturer’s processes at several different stations that check precise weights of individual and pallet compressors and electronic monitors at the filling station make it hard to pass through. To be on the safe side always check your new compressor for oil.

Before installing a new compressor, you must check the oil quantity and the viscosity according to the manufacturer’s instructions and refill as needed!

Effects of failure

A damaged or failed compressor can manifest itself as follows:

  • Leakage
  • Development of noise
  • Insufficient or no cooling performance
  • Error code in the air-conditioning control unit or engine/central control unit

There are a number of possible causes of failure:

  • Bearing damage caused by a defective tensioner or by wear
  • Leaks in the compressor shaft or the housing
  • Mechanical damage to the compressor housing
  • Contact (electrical connections)
  • Electrical control valve
  • Lack of refrigerant oil
  • Lack of refrigerant
  • Solids (e.g. swarf)
  • Humidity (corrosion etc.)
  • Defective tensioning elements and ancillary units


Function test and pressure measurement of the system:

  • Does the compressor switch on, is the connector plug securely in place, is power applied?
  • Check the electrical control valve and/or the activation circuit.
  • Check that the drive belt is positioned correctly, undamaged, and that there is power.
  • Check visually for loss of sealing.
  • Check that refrigerant hoses are securely in place.
  • Compare the pressures on the high and low-pressure sides.
  • Read out the event memory in newer systems.

It is extremely important to replace all O-rings and wet them with refrigerant oil before installation. Before installing a new compressor, you must check the oil quantity and the viscosity according to the manufacturer’s instructions and refill as needed! The entire air-conditioning system must be flushed and the consumables and any components that cannot be flushed must be replaced when the compressor is replaced!

Tips on replacing a Compressor

PROBLEM: Air-conditioning system is not cooling properly – Louvre temperature should be about 30-40 degrees Fahrenheit cooler than ambient temperature.

DIAGNOSIS TIPS: Inspect the following items before assuming the air-conditioning system is faulty:

  1. Vehicle cooling system is operating correctly by blocking the airflow in front of the radiator grill and checking that the thermostat is operating. Also check that there are no water leaks in hoses or fittings.
  2. Check that the belt tension is correct to manufacturer’s specifications – No “squealing”.
  3. Check that the condenser fins are clear of obstructing objects – Mud, dead flying insects, paper etc.
  4. Check that the evaporator drain tube is clear.
  5. Check for loose wires on all plugs and switches under the hood that might have any control over the air-conditioning system.
  6. Look for any build-up of dirt at any joints or fittings on the air-conditioning system that may indicate a small system oil leak.

PROBLEM: Air-conditioning system is not cooling properly – Louvre temperature should be about 30-40 degrees Fahrenheit cooler than ambient temperature.

Now we have eliminated the external possible issues. The system we are working on is a GM Clutch Cycling Orifice Tube system.

WARNING: You are about to start working on the air-conditioning system which is charged with refrigerant at high pressure. DO NOT attempt to remove any system parts or to loosen fittings until the system has been properly discharged.


  1. Switch on the engine and turn on the air-conditioner; open the hood and observe whether the clutch pulley and armature plate are both rotating. It might be helpful to get an assistant to switch the air-conditioner on and off. Look for the armature. plate rotate and stop while the switch is operated.


  1. Switch off the engine.
  2. Check that the clutch wire is connected – IF NOT – Connect and repeat the 1st step.

IF IT IS ROTATING – Remove the clutch wire and carefully open the plastic retaining tags. Connect the positive wire of a multimeter to the clutch wire and the negative wire to Earth.

Note: If the clutch has two wires connect both multimeter wires. The mulitmeter should be set to the voltage scale.

  1. Switch the ignition but be sure to NOT START THE ENGINE. Turn on the air-conditioner and check the multimeter scale. IF NO voltage, check the fuse block for a blown fuse and replace the fuse. Go back to the 1st step.
  2. If there is voltage proceed to the next step.

PROBLEM: Air-conditioning system is not cooling properly – Louvre temperature should be about 30-40 degrees Fahrenheit  cooler than ambient temperature.

Now we have eliminated the external possible issues. The system we are working on is a GM Clutch Cycling Orifice Tube system. No or low cooling; the clutch wires are hot when the air-conditioner is switched on, but the clutch is not engaging.

WARNING: You are about to start working on the air-conditioning system which is charged with refrigerant at high pressure. DO NOT attempt to remove any system parts or to loosen any fittings until the system has been properly discharged.

DIAGNOSIS PROCEDURE & TIPS – Removing the compressor:

  1. Connect up your gage, set blue to the low side and red to the high side. Open the blue valve and check to see if the needle moves. If it does there is refrigerant in the system.
  2. Connect up your refrigerant recovery unit as per the manufacturer’s instructions and pump out the refrigerant from your system. Measure the amount of oil collected in the unit and record.
  3. Ensure that ALL refrigerant is evacuated by turning off the recovery machine for 5 minutes and checking that your gauges are still reading zero or vacuum. Close all shut off valves.*
  4. Disconnect all service lines and move the compressor to the bench.
  5. Connect a multimeter set to the resistance scale and the multimeter leads to the clutch connections. Where appropriate observe polarity as there may be a diode in the coil circuit. The meter should read ~ 3 Ohms (12V system). IF IT DOES, check that the clutch gap is set to 0.3 to 0.7 mm. IF IT IS replace the compressor. IF NOT, correct and apply 12 volts to the coil connector while observing the polarity. If the coil now engages, it is likely that this problem is solved. Refit the compressor and follow the next step.

*Note: It is a federal offence to discharge refrigerant into the atmosphere.

PROBLEM: Air-conditioning system is not cooling properly – Louver temperature should be about 30-40 degrees Fahrenheit cooler than ambient temperature.

Now we have eliminated the external possible issues. The system we are working on is a GM Clutch Cycling Orifice Tube system. No or low cooling; the clutch wires are hot when the air-conditioner is switched on but the clutch is not engaging. The clutch gap was hence adjusted so that it is working now.

WARNING: You are about to start working on the air-conditioning system which is charged with refrigerant at high pressure. DO NOT attempt to remove any system parts or to loosen the fittings until the system has been properly discharged.

DIAGNOSIS TIPS – Replacing the compressor:

  1. Measure the amount of oil found in the recovery machine into a beaker and put this into the compressor on the suction side or through the filler port provided.
  2. Fit the compressor to the vehicle replacing all o rings and seals with new ones and lubricate them with compressor oil.
  3. Reconnect the drive belt and clutch wires. Remember to check whether the clutch is working!
  4. Connect up your gauge and then set blue to the low side and red to the high side.
  5. Connect up your vacuum pump per the manufacturer’s instructions and ensure that the low side gauge registers 30 in Hg. Leave this running for a minimum of 30 minutes. Turn off the pump and close the manifold gauge valves. Watch the low side gauge for movement towards 0 indicating a leak. If there is NO movement proceed to the next step.
  6. Connect a cylinder of refrigerant R134a to the yellow inlet hose on the manifold set. With the cylinder upright (Vapour charge) and the cylinder shut off, open the valve slowly. Undo the connection at the manifold and discharge a small amount of refrigerant from the hose line to express any air present. Do this for a maximum of 2 seconds.
  7. Set the cylinder on a weighing scale and open both manifold valves. Charge the system with the correct amount of refrigerant as per the vehicle manufacturer’s label.
  8. When completed CLOSE both manifold valves…
  9. Remove the gauge set and go to the next step.

PROBLEM: Air-conditioning system is not cooling properly – Louver temperature should be about 30-40 degrees Fahrenheit cooler than ambient temperature. Now we have eliminated the external possible issues.

WARNING: You are about to start working on the air-conditioning system which is charged with refrigerant at high pressure. DO NOT attempt to remove any system parts or to loosen any fittings until the system has been properly discharged.

DIAGNOSIS TIPS – Analysing a charged system with a rotating compressor:

  1. Leak check the system using an electronic leak detector. Turn on the detector and slowly move the probe along all refrigerant lines. Pay particular attention to all fittings and connections. Check the plastic tops of all switches in the refrigerant lines as that joint is prone to leaking. Carefully place the probe by the evaporator drain tube (NOT in it). If NO leaks are sensed proceed with the steps below. If there is a leak, repair it and recheck.
  2. This will entail discharging the system with the recovery machine.
  3. If all is in order, connect your manifold gauge: set Red to high side Blue to low side.
  4. Make sure both valves are closed. Pressures should be approximately equal in both sides. Insert a thermometer in the centre vent.
  5. Start the engine at idle set air-conditioner to the minimum/coldest temperature and open all the doors of the vehicle. Place a shop fan in front of the condenser and switch on. Take note of the ambient temperature. (70 degrees Fahrenheit and above is best)
  6. High side gauge should increase and low side gauge should reduce.
  7. Check whether the louver temperature is within specification…If it is your problem has been solved! If not…
  8. Gauges should read:
    • High ~200 to 250 with a 75 degree Fahrenheit ambient .
    • Low side will be ~25 to 35 at the same ambient.
  9. If both gages are reading significantly lower – check the expansion valve or OT for condensation (indicating a blockage or malfunction) If this is so, this item should be replaced. Connect recovery unit, discharge the system and remove and replace the faulty part.

Tips on replacing a compressor clutch bearing

Problem: Noisy clutch operation with a wobbling pulley and excessive belt wear. These can all indicate a badly worn pulley bearing.

WARNING: You are about to start working on the air-conditioning system which is charged with refrigerant at high pressure. DO NOT attempt to remove any system parts or loosen fittings until the system has been properly discharged.


  1. Connect up a certified recovery unit and remove all the refrigerant into an appropriate container.
  2. Remove the compressor from the system and replace the shipping caps on the suction and discharge ports to prevent oil loss.
  3. Mount the compressor in a suitable holding fixture or vise.
  4. Using the appropriate extraction tool to remove the armature plate.
  5. Measure the belt gauge line on the compressor from the front cast mounting point to the first groove and record the measurement.
  6. Remove the pulley snap ring using a three jaw extractor. Carefully remove the pulley without bending the clutch face. If this face is bent the clutch may not function correctly.
  7. Typically these bearings are stacked. To remove the bearing support the bearing housing with a steel pie or cup of the appropriate diameter and push the bearing out with a hydraulic press from the front of the clutch to the back.
  8. Apply Red Loctite sparingly to the outer diameter of the new cleaned bearing.
  9. Locate the bearing on the rear of the pulley bearing housing. Take a ¼ inch flat steel plate of the appropriate size to fit within the rear of the pulley and place the assembly on the bed of the press.
  10. Push the bearing into the pulley housing until heavy resistance is felt. NOTE: do NOT push the bearing into the housing using the bearing inner race as this will destroy the bearing. Wipe any surplus Red Loctite from the assembly.
  11. Using the same ¼ inch plate, assemble the pulley onto the compressor nose. The plate must be used to protect the clutch face.
  12. Check whether the belt gauge line dimension recorded earlier is correct.
  13. Carefully tap on the armature plate (front plate) and check the gap with a feeler gage all the way around. The correct gap should be 0.3 to 0.7 mm.
  14. Spin the clutch pulley by hand and check whether it is quiet and running true.
  15. If everything is in order, refit the compressor, evacuate the system for 45 minutes at 29,9 in Hg and recharge with the appropriate refrigerant charge noted on the vehicle air-conditioning system plate. NOTE: only certified R134a to SAE J2099 refrigerant, which does not include any additives, should be used.

Clutch Protection Equipment

When a compressor fails and the clutch locks up sparks, flames and bits of rubber fly everywhere. The engine then dies after 20-30 miles because it has overheated or the battery went flat, because the serpentine belt came off or broke when the compressor failed.

Fortunately, many manufacturers are adding safety devices to the clutch to prevent this happening. They take many forms.

  1. Speed sensing devices which tell the vehicles air-conditioning system control that the mechanism is not rotating and hence shuts down the air-conditioner clutch voltage.
  2. Temperature sensing devices which are embedded into the clutch coil winding, which open the clutch circuit if the temperature reaches a catastrophic value. This device (unseen) opens the clutch circuit and allows the pulley to continue to rotate hence allowing you drive to the nearest air-conditioner shop albeit with the windows down to keep cool.

Compressor Drive Belt Maintenance

There are several factors that have major effects on compressor drive belt life expectancy and reliability. Belt alignment and proper tension are the two most critical and are controllable by the installer and end user. When improperly installed or maintained, drive belts can cause significant damage to the compressor and clutch and other components and pose a safety issue. Never use compressed “shop” air to leak or pressure test an air-conditioning system. Under certain conditions, pressurised mixtures of refrigerant and air are combustible. In addition shop air will inject excess moisture into the system.


When contaminants build up on the evaporator fins, such as dirt, dust and other debris, its ability to absorb and remove heat from the cab can be severely reduced as well as restricting the air flow. To maintain peak performance, regularly clean the fin area with a fin comb and solvent and change the cab air filter if applicable. Take special care to not bend or damage the evaporator fins in the process.

Expansion Valves

Expansion Valves come in two types: Block and Right Angle. The block valve is located at the evaporator and its purpose is to constantly check the temperature of the R12 or R134a and allow the proper amount of refrigerant to enter the evaporator. The right angle valve comes in two types (internal equalised and external equalised). This valve is also found before the evaporator and its purpose is to control the amount of refrigerant going into the evaporator.

The most common block valve failure is loss of gas charge inside the power element head. Plugged expansion valves cannot be flushed out and must be replaced. When replacing a capillary type expansion valve make sure the capillary coil or bulb is properly attached to the outlet side of the evaporator line and well insulated with prestite insulation tape.

The most common expansion valve failure mode is due to valve charge head leaks… System contaminants lodged in the valve inlet orifice may also affect valve metering and flow capabilities. Suspected metering inconsistencies may, over time, have distinct characteristics. On a starving Expansion Valve frost will form on the inlet of an evaporator. On a Flooding Expansion Valve a hissing sound will occur upon system shutdown.

Did you know?

The expansion valve is a refrigerant metering device that creates a temperature/pressure drop. It also divides the system into two zones, high pressure and low pressure.

Receiver driers

The receiver drier stores excess refrigerant, filters out any contaminants that may be in the system and removes moisture from the liquid refrigerant to protect the system from internal corrosion. Placement should be between the condenser and evaporator inlet and should be warm to the touch with the air-conditioner running.

When either installing a new air-conditioning system or doing a service job always make the drier the last component replaced before evacuation and recharge. The desiccant in the drier absorbs moisture and will decrease performance and create a problem to the system at a later date. Moisture and refrigerant when combined creates an acid and will damage the internal parts of the air-conditioning system.

The receiver drier filters out contaminants in the air-conditioning system and removes moisture to protect the system from internal corrosion. Never leave the drier uncapped prior to installation and should be the last component replaced during any service of the HVAC system. In a preventative maintenance schedule it is recommended the receiver drier be replaced every 12 months.

Did you know?

The receiver drier should be replaced anytime the air-conditioning system is opened and never leave the fittings uncapped prior to installation. If you do throw it away.

When performing any service on the HVAC always make the receiver drier the last component replaced.


Always be aware of Refrigerant Replacements. R-415b is being touted as an R12 and in some cases an R134a replacement. This refrigerant ASHRAE: R-415b(25% HCFC-22 / 75% HFC-152a) is a BLEND and is also highly flammable. We at MACSauto do not recommend the use of this blend for any of our customers.

If pressure readings were diagnosed to require a refrigerant adjustment, then most likely it was determined that some loss of refrigerant has occurred. Depending on the amount that needs to be added, how serve is the problem? Was it a very small amount that could be caused through normal permeation or a larger amount indicative that a repair is required? In either case, the correct thing to do is to carefully go over the system and fix any leak that can be identified. It will get worse if not repaired. Best practice is to fix any leak that can be identified.

Have a look at the Mobile Air Conditioning Society (MACS) Worldwide blog to receive the latest news on mobile air-conditioning and for some great tips and expert advice!

Tools and Accessories

Orifice Tubes

The orifice tube often has a mesh screen and is found in the evaporator inlet pipe. In some cases this item is found in the outlet of the condenser. Its purpose is to limit the flow of the high pressure liquid and thereby meter the flow of refrigerant to the evaporator as a lower pressure liquid. The screen serves the purpose of trapping metal particles that break loose from the compressor or other components.

GM Pressure Switches

There are 4 different function switches on GM systems that operate with pressure. They are:

  1. High Side low pressure switch (HSLP) – This switch monitors the high side pressure and prevents the compressor from switching on when the pressure drops below ~8PSIG. This prevents the system from operating in sub-freezing conditions.
  2. High Pressure Switch (HPS) – This switch monitors the high side pressure and prevents the compressor from switching on when the pressure drops below about 25-40 PSIG.
  3. High Pressure Cut Off switch (HPCO) – This switch shuts the compressor off if the high side pressure exceeds ~430 PSIG.
  4. Engine fan switch – This switch operates the engine cooling fan based on the high side pressures. It closes to turn the fan on when the pressure reaches 230-280 PSIG and opens when the pressure drops to 160 – 210 PSIG.

It is recommended to install liquid line filters and suction screens when previous system failure was the result of compressor, accumulator, or receiver drier failure. Additionally, flushing the system with refrigerant is recommended.