I bought this car used and the guy who sold it said the AC worked - well, when I press the AC button on the dash, the little green light goes on but no cold air - it blows warm. I pop the hood and the AC clutch is not engaging. I put R12 gauges on it and its full.

I discovered a butt connector connecting the one red wire going to the AC clutch and how a little wire going into the connector is bare. With the AC button on, I probed the wire and the exposed part with a 12 volt tester. No juice going to it.

I am thinking maybe the wire hit a metal part and blew a fuse. Where is the fuse for the AC clutch? I check in the fuse panel on the dash but I dont see one for the AC system. I then saw a fuse panel near the passenger side fender in the upper corner and checked the large fuses (4 or 5 of them) with a continuity tester and all were good. The normal sized fuses looked good as well. There also were three black plastic fuses (I assume) but I couldn't check them, since they had 4 blades.

Anyone?

 

Does the condenser fan come on and the engine rev up when you push the A/C button?

I think the fuse is one of the small ones in the underhood box. The four-pin things are not fuses and they aren't related to the A/C. There are two relays next to the condenser for the A/C, one for the fan and one for the compressor. Also pull the plug off the refrigerant pressure switch and check the switch for continuity, which it should have if really full. You need at least about 50 psi to close the switch.

 

The four pin things are relays, not fuses. One of them is probably the A/C compressor clutch relay. This relay is important sicne it provides power to your A/C clutch. Fuse 35(20A) and fuse 13(7.5A) are the two fuses that are used in the A/C system, make sure they are working. There is an A/C pressure switch and a A/C thermo switch. If either of these switches are open, the clutch will not receive power. I would think you can narrow down the problem by hard wiring the A/C clutch to power. The way a relay works is that there is a coil and a switch. When the coil is energized, the switch closes. What you can do is remove the relay and short the two pins that are for the switch part of the relay. You can check which two pins this is with a meter. The 2 coil pins will have a resistance. You don't want to put the wire b/w the two pins on the relay but to the two holes in the fuse box. This should send power to the clutch and the clutch should engage. Be very careful when doing this. I would recommend doing it while the engine is not running and look and see if the clutch engages. If you have teh clutch engaged too long, you can blow the compressor. There is a reason why your clutch is not engaging and this could be b/c there isn't enough refrigerant. Refrigerant has lube in it as well. If you don't have refrigerant and lube, your compressor could blow up. I am not resposible for any damage that occurs while conducting these tests.

 

If the engine does not rev up after pressing the button, it is likely the thermo switch or pressure switch (or inadequate pressure).

Do not jump the compressor with the engine running at all as there is no protection against excess or insufficent pressure then. The compressor is about a $450 part, so baby it.

 

If you do it for an instant, just enough time to see if it enganges or not, it should not due any damage to the compressor. Either way, it should also work if the engine is not running which is the best way to do it.

 

Problem solved! Here there is a relay that was loose - the plug was together but not clicked in. The relay was attached to the radiator core support on the drivers side. I pushed it together tight and the clutch engaged and now I have cool air!