Tech Tip: Several Expensive Parts could be the Culprit when an A/C System Goes Down

Tech Tip: Several Expensive Parts could be the Culprit when an A/C System Goes Down

A/C compressors are usually the most expensive A/C component to replace, followed by condensers and evaporators. So it is very important to make sure (1) the compressor is really bad and needs to be replaced, (2) the cause of the compressor failure has been identified and fixed so the new compressor does not fail for the same reason, and (3) the new compressor is installed properly and lubricated with the correct type of compressor oil ....

By Larry Carley
Technical Editor

A/C compressors are usually the most expensive A/C component to replace, followed by condensers and evaporators. So it is very important to make sure (1) the compressor is really bad and needs to be replaced, (2) the cause of the compressor failure has been identified and fixed so the new compressor does not fail for the same reason, and (3) the new compressor is installed properly and lubricated with the correct type of compressor oil.

The most common cause of compressor failure is inadequate lubrication. This may be the result of a refrigerant leak that allows compressor oil to leak out of the system. Typical leak points are hoses, hose and pipe connections (O-rings and flange gaskets), the evaporator, condenser or the compressor shaft seal. Leak detection dye or an electronic leak detector should be used to find the leak so it can be repaired.

Lubrication problems can also be caused by a blockage (typically the orifice tube) that prevents refrigerant and oil from circulating through the A/C system.

Using the wrong type of compressor oil for the application or the wrong amount can also lead to premature wear and failure. There are various grades of PAG oil, and using the wrong grade can cause problems. Always use the type of PAG oil specified by the compressor manufacturer or vehicle manufacturer. Use only the amount specified for the compressor. Adding too much oil can cause cooling problems.
Mineral-based compressor oil is only for older vehicles (pre-1995) with R-12 compressors, and should never be used with a compressor in an R-134 A/C system.

A compressor may also fail if there is sludge or debris inside the A/C system. Moisture contamination of the refrigerant can form acids that attack metal surfaces and form sludge inside the system. Over time, this can gum up and damage the compressor. If the system contains any sludge or debris, the hoses, evaporator and condenser should all be flushed out to remove the contaminants. Note: some condensers cannot be flushed due to the way they are constructed, so replacement is necessary if the condenser is contaminated.

A compressor may also have to be replaced if it is leaking, making excessive noise or not working correctly because of an internal valve or piston failure. Some compressors are naturally noisier than others, but loud knocking noises can sometimes be caused by air in the system. The cure in this case is not to replace the compressor, but to recover the refrigerant from the system, then vacuum purge the system for 30 minutes to an hour with an A/C vacuum pump to remove the unwanted air. If the compressor is still making noise after the system has been purged and recharged, it probably needs to be replaced.

When a compressor fails, it may spew out metallic debris. Most of the junk ends up in the condenser, but some may travel as far as the orifice tube or be blown back into the suction hose. If this junk is not flushed out of the system, it can be sucked into the new compressor and cause it to fail, too.

When a compressor is replaced, the accumulator or receiver/drier should also be replaced. The accumulator or receiver/drier contains a bag of desiccant that absorbs moisture. This helps to protect the A/C system against sludge. But over time, the desiccant becomes saturated and cannot hold any more water. If the A/C system has been opened up for repairs, or has lost its charge of refrigerant, humidity in the outside air can enter the system and overload the desiccant. That’s why it needs to be replaced.

Another component that should also be changed when replacing a compressor is the orifice tube. This small plastic tube meters refrigerant into the evaporator. If it plugs up, it can block the flow of coolant, causing the A/C to stop blowing cold air. It can also starve the new compressor for lubrication because the oil circulates with the refrigerant.

A couple of preventive measures can also be taken to protect a new compressor. One is to install an in-line filter in the high pressure liquid line to catch any debris that might come out of the condenser. Another is to install an inlet screen filter in the suction hose to stop any debris from being sucked into the compressor.

Other A/C components that may also have to be replaced when changing a compressor include the magnetic clutch (if it is worn or slipping), the drive belt and A/C hoses. Refrigerant that contains leak detection dye can be used to recharge the system. After the dye circulates awhile, it will reveal any leaks that might have been missed and need to be repaired.

You May Also Like

Manual Transmission Failure Causes

One of the most common reasons behind why a manual transmission fails is lack of lubrication.

The most common reasons behind why a manual transmission fails are lack of lubrication, incorrect lubrication and improper or no clutch release.

COMPLEXITY OF LUBRICATION

Lubrication should be simple, but in the modern world NOTHING is simple. There was a time when virtually all stick transmissions ran on 90w gear oil. The synchronizer rings were brass or bronze, the cars and trucks shifted around 3,000 rpm and we had 3- and 4-speed transmissions. Ninety-weight did not like cold weather and generated multiple complaints to the manufacturer due to cold-shift problems. You needed two men and a boy to shift one of the units on a cold day until the fluid heated up.

Wheel Bearing Hub Damage Repair

Noise is a classic sign of a bad wheel bearing or wheel hub bearing. Determining why the damage happened may take some time.

Electric Vehicle Battery Service

Don’t be afraid to work on battery packs. However, you should be mindful of the potential damage high voltages can cause.

ADAS Suspension Alignments

Look at the “big picture” and really consider how the vehicle will operate if things aren’t done correctly.

Building The Perfect Future By Mentoring

Share your stories of how you have helped others reach their goals.

Other Posts

Electric Power Steering Diagnostics

Load management for steering systems.

GRI Receives US DOT Certification For Safety

GRI tires will now incorporate the DOT code emboss on its side walls.

Active Ride Control Diagnostics

The key to servicing these systems is proper information and understanding precisely how these systems operate.

Brake Pad Errors and Mismatches

In order to make the right selection, you must do your homework while still remaining skeptical.