AC Compressor troubleshooting
The air conditioning compressor is one of those parts of the car that are typically used for long hours and typically gets a lot of usage. It has been seen that AC compressors are generally reliable and don't fail easily. 
If it does, it is often because of some other reasons. The point is, never replace a compressor in a hurry without detecting the full problem. Otherwise it is quite likely that the new one will also fail. 

Why AC Compressors fail
Before we go on pinpointing the reasons for faulty compressors let's understand its working. 
As the name suggets AC compressors compresses refrigerant and sends it to the air condenser of a car. Engine's drive belt (or belts) powers the entire process. As the highly pressurized liquid refrigerant turns into gas, it is then circulated into tubes. This process makes heat dissipation from the gas really fast and causing it to cool. By returning to the compressor, the cooled gas goes back into liquid form and the cycle is repeated. It is the cooled gas which makes the car's interior air cool. Let's take look at some of the common problems. 

    • Clogged/Dirty Evaporator or Condenser Fins
    • Loose Fan Belts
    • Use of improper refrigerant (other than R-134A)
    • Wrong adjustment of expansion valves
    • Unadjusted controls
    • Worn out compressor clutches

Diagnosing the problem Generally, the problems are diagnosed as mechanical or electrical failure. Let's deal with them one by one. 

Mechanical failure
The most common problem is the leaking out of the refrigerant from the compressor. This generally happens due to wear and tear in piston or bearing rods. As compressors compresses refrigerant into vapor it will naturally turn very hot. But in case of any fault you will notice that the pipe coming out of the compressor is not really hot and the outlet pipe of the condenser is not freezing either. Another very common problem is that of liquid slugging. It occurs when liquid refrigerant and oil flows together and get collected at the bottom of the evaporator or in the suction line. So, as soon as the AC system starts these enter the compressor damaging the rods, piston, valve plates and / or blows the gaskets. A leakage from the gasket is then imminent. Loose Fan belts should be checked and tightened if required. Evaporator or Condenser Fins should also be checked for ruling out any possibility of clogging. 

Electrical Failure After checking for all the mechanical ones it is time to know whether it might be an electrical failure. When the AC is switched 'ON' while the vehicle is stationary, a sudden change in engine noise is observed. Or, when the vehicle is moving as soon as the AC is switched there is sudden power drop. 
These might be due to malfunctioning of Compressor relay. Normally any automobiles relay works efficiently for 5 years so they must be periodically checked and changed. Generally electrical failure cannot be properly diagnosed by naked eye, proper tools are required for that. Taking professional help will be a good option. 


In the event of a mechanical failure it requires replacement, while in electrical failures replacing the electromagnet and clutch assembly sorts the problem. Anyways AC compressor should be checked on regular basis for increasing its life span. 

Good Brands 

Generally DENSO, DELPHI, and BOSCH are OEM supplier to all automobiles in Nigeria so it is best to replace Compressor recommended by OEMs. Other brands might solve the problem but obviously might not suitable for long time. You can find the name of Manufacturer’s name engraved on your Car’s compressor along with model number. 



Old car: compressor is giving knocking sounds after staring

Car might have done more then 20000 km. Due to wear tear, internal parts of the compressor got damaged; along with Pulley Clutch, get the AC compressor checked, get it replaced if required.

Cooling has become inefficient, old cars have these problem

Check for internal blockage in pipes, air vents and proper Refrigerant level along with the oil.
Every car is fitted with a pre-designated size of compressor denoted by cc. Now as it becomes old efficiency drops. Upgrades with higher cc can be done. For example if stock compressor was 70cc then going for 75-80CC with the dryer bottle is a good option. It will slightly increase the engine load, but would improve cooling.

Screeching sound after turning on AC; becomes silent or continuous sound heard there after

(a)Check for Loose Belt; properly tighten it. If problem neglected for long then belt has to be replaced as it becomes hard. Loose belts tend to get heated and might change shape. 
(b)Continuous sound -Pulley Bearing worned -out ; replace bearing; no use trying to lubricate bearing.    

Refrigerant problem in old car

Old cars filled with R-12 grade Refrigerant, which is less effective and harmful to atmosphere that damage ozone layers. Flush it with new CFC R-134A Refrigerants, more effective, will drastically change the cooling effectiveness.

Posted on November 2015,21  //  Author: Admin