Hey everyone, just found out with the warmer weather coming through that the air conditioning and cooling fans on my 97 Aurora don't work at all. There is no click coming from the compressor when I push the AC button and the cooling fans don't work even when the engine gets hot. The engine never gets critically hot (it goes to just under 240 degrees during severe stop and go but often stays about 220 in regular stop and go and cools down to just under the center point in continuous driving). The AC blows hot air even on the coldest setting.

To me it'* clear either the AC or the cooling fan is preventing the other from turning on because the computer shouldn't let the AC turn on if the fan doesn't work and the two relays are probably linked together in some way that effects the other.

I've tried moving the smaller relays (one of them for the AC compressor) around to make sure that wasn't the issue but it hasn't changed anything. Could both the large cooling fan relays be bad? I don't know much about relays so I couldn't test them. It'* also possible the wiring is bad from the fans to the relay box but I'm not sure where the wiring is located as it'* pretty tight in the engine bay.

I've done the basics like checking that the major fuse for the AC or cooling fan was still good but I have not gone much further.

What'* a good place to start in figuring out what the problem is? I'd like to see if I can jump the fans from the relay block but I don't know which holes to insert the jumper wire into.

Thanks a lot!

Just took a further look and there doesn't appear to be anything obviously wrong with the wiring.

I plugged in my scan tool and pulled one code when I tried to activate the windshield defrost: P1537 "A/C Request Circuit Voltage Low" which, under my interpretation, seems to indicate that the clutch is not engaging for one reason or another. Am I correct?

Of course I can't actually hear whether or not the fans are coming on at high temperature but I am inclined to believe they are not since the temperature doesn't really come down and I have opened up the hood while it was fairly hot and the fans were not spinning.

Is there another way to force the fans to come on like by disconnecting a sensor?

Sounds like you might have 2 issues. I'm betting the freon is low causing the low pressure switch to stay open not allowing the A/C clutch to cycle. As far as the cooling fans the ECM should command them on around 225. You can pull the fan relay and jump terminal 30 and 87 with a jumper wire and see if the fan turns on. If it don't unplug the fan and check for power and work back words. Having a scanner you can command the fans on with helps and being able to monitor what reading the PCM is getting from the coolant temp sensor helps as well but without them you can do the relay trick to see if it is a power or ground problem or if the problem is on the command side.

Low freon was my first thought also, you can get a recharge kit from your local auto parts store, I recommend AC/Pro, I have also used Interdynamics Arctic Freeze also, works pretty well.

If you need help on how to recharge it check out this video.

I will try jumping it to see if they come on, then check if there'* any power going to the fans from the one connector on the front I see.

I was fairly confident the AC is low on Freon as well, but I'm not sure if I should go out and attempt to refill yet because if the fans won't come on the compressor won't either and I'll end up wasting the canister if I can't get the pump to suck in the freon.

It'* possible some kind of temperature sensor is going out and not commanding the fans on as I vaguely recall driving down the road, needle about 200, and the display flashed for a split second either engine hot shut down or low coolant, but the coolant is full and the needle was again at 200. Has never happened since and never thought much about it.

Unfortunately as far as refrigerant goes I'm stuck with whatever I can get here because it'* illegal to have r134a without a license so it'* going to be the Red Tek kit which is actually R12a. Not sure about vacuuming out the old stuff.

I don't think R134a is backward compatible with R12.


Try disconnecting the coolant temp sensor while the engine is running. If the fans immediately turn on, then they are operational.


Otherwise, its like already mentioned. The fans are programmed to come on at like 212 and 226 for dual fan setup. The operational status of your A/C system does not affect the cooling fan side of things.

Read this via google..

"the oils used by R12 and by R134a are different and not compatible. If mixed, they form an acidic sludge that is bad for the system. To properly switch from one to the other, you need to evacuate all oil and change the receiver/drier (which will have some of the old oil absorbed in it). Also, R12 is currently about $60/lb. This would be a very expensive option."

Good research Will.

Mike, Will, R12a (more correctly HC12a) is not the same as r12 and the name does confuse people. The R12a is designed to be compatible and from what I've read will mix right in with whatever'* left of the r134a, if there is any left, and anything saying you can't is because of the laws here regarding mixing refrigerants.

I will disconnect the coolant temp sensor and I'll at least know if the fans are working before trying anything else.

Thanks for your help!

Good catch, it sounds like R12a will work in a system normally using R134a, but don't most of those cans of R12a say something on them like "Evacuate the system. Do not mix refrigerants." ?

Like take this product for example, are they saying you should not mix them just because it is not legal?
RED TEK - 12a Refrigerant

5) Determine the type of refrigerant currently in the a/c system. The OEM tag is located inside the engine compartment. The OEM tag indicates the type and amount of refrigerant in the system. If missing, contact the OEM for further information. This must be determined before initiating a RED TEK® 12a recharge.
6) Evacuation of the refrigerant in the system is recommended prior to installing RED TEK® 12a refrigerant. Recover all existing refrigerants into a suitable approved container and mark appropriately, as FEDERAL REGULATIONS PROHIBIT THE VENTING OF REFRIGERANTS INTO THE ATMOSPHERE. Although RED TEK® 12a is compatible with most existing refrigerants and oils, DO NOT MIX REFRIGERANTS. Mixing refrigerants is illegal in Canada and the US and will not offer the maximum performance available from RED TEK® 12a.