Auto Repair Q&A



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Air Conditioning Diagnosis

Typical AC Layout

Two things commonly lead to air conditioning (A/C) problems in a vehicle: leaking refrigerant and a bad AC pump. In many states, the way you handle air conditioning components is heavily regulated. You are not, for instance, allowed to vent refrigerant or replace refrigerant in a leaking A/C system.

So know the laws where you live before you proceed to do it yourself. Most likely, you'll have to consult with a licensed professional at some point.

If the problem is a leaking system, then you'll have to find the source of the leak. If the problem is a bad pump, then you'll have to replace the pump. To test the pump, it has to be removed from the system, which requires venting and that is heavily regulated. To find a leak, all you need is for the engine to be running and access to all of the A/C lines.

Typical AC System Layout

Checking A/C Lines for Leaks

So check for leaks first. Get a bottle of water with a little bit (a few drops) of dish soap. There are also colored soaps for easier visibility available in auto parts stores - look for "diagnostic spray."

Spray the lines at each joint with the engine running and the A/C on. Watch for bubbles forming where you've sprayed. If you find no leaks, spray up and down each line to see if there are leaks in the lines themselves. If no leak is found, you'll have to empty the lines and remove the pump for testing.

Venting the A/C System

Regulations require that the vented gases be captured. There are machines made for this purpose and most qualified A/C technicians will have one. You can also hire someone just to vent your A/C for a reasonable price at most auto maintenance garages and sometimes at auto parts stores.

Do not vent the coolant into the atmosphere!

Checking the AC Pump

Once the coolant is vented, you can safely remove the AC pump from the vehicle. This is usually two bolts and the removal of the attached lines from the pump.

Once the pump is off, have it tested. A technician will place the pump on a machine, plug into the input and outlet lines, and use an electric motor to turn the pump's pulley. The machine will test the pump's compression ratio and determine if it's working.

Replace the pump if necessary and refill the coolant. If your vehicle uses the newer 134 coolant (most vehicles made after 2000 do), then you can probably buy it at the auto parts store and do it yourself. There are nubs on the coolant line made to receive the hose from an A/C refill can. If your vehicle uses the older R-12, you'll have to hire a licensed technician to do it.

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