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.


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.


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.


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.



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.


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.

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