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A/C problems not caused by leaks

Auto AC system

Air conditioner (A/C) problems are frustrating to many car owners. For one, they never seem to happen (get noticed) until it's hot and you want the cold air on in the car. They also seem to always be something that isn't obvious and cannot be fixed by simply buying a cheap can of refrigerant boost and adding it to the system (we've all tried that in hopes it would work). If there are no leaks in the system, then the problem can be narrowed to either a defective A/C pump (which we've covered before, click here) or something electrical.

To start with, have a professional who's licensed to do so (there are legal reasons for this) check your system for leaks. This will involve attaching a gauge to the high pressure side of your air conditioning system and checking pressures or inducing pressure to see if it drops due to a leak. If there are leaks, that's is almost always going to be your problem when the A/C stops working. If repairing the leak doesn't fix the problem, you've likely at least found the source for it. Next is the compressor, which you should check to ensure it's working. Do this by going through the electrical system first.

Pressure sensors

Obviously, if you have an engine light or warning, pull the codes. If they are A/C-related, they are likely pointing to your problem. That's probably going to be one of the pressure sensors. Most vheicles have a low-pressure sensor on the high-pressure side of the system. This sensor detects when pressure is low and cuts off power to the A/C clutch in order to preserve the pump, which requires refrigerant for lubrication. When refrigerant pressure is low (indicating a lack of refrigerant in the system), the pump could burn itself out if it continues running so the low-pressure sensor acts as a cutoff.

Some systems have a "leak sensor" which does much the same thing, but operates on the low-presssure side of the A/C system to detect a high disparity between the pressure reading from the high-pressure side and its reading of the low-pressure end. This is most-often found in European vehicles.

Check the relays, switches

Most air conditioning systems have at least one relay to control the A/C pump. Most also have a switch for it. Check all of the fuses related to the A/C and replace any that are blown. The switch is often found on the pump itself while the relay will be in the engine's fuse box. The switch can be tested by simply removing it and putting 12V power to one side and testing output on the other, which should be about the same. If it isn't, replace the switch.

The relay can be tested by removing it and either replacing ti with a new one or with another from the fuse box that is of the same part number (there are likely several). If the pump engages, then you know you need a new relay.

Circuit Checks

If none of the above is the issue, then you might have a short in the A/C circuit somewhere. You'll have to trace from one end to the other, section by section, to find it. Start at the pump if you can, as your likely spots are going to be closer to it than to the fuse box or power source.

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