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Air conditioner shuts off when driving but works when stationary

My 2001 SAAB 93 has this weird problem. The air conditioner works great when the car is not moving but within 50 -60 feet of moving it shuts off and blows hot air. This doesn’t sounds like a big problem but when it rains the condensation builds up to the point that all I can do is to pull over, turn off the engine, wait 10 minutes, turn on the engine and then the cold air will clear the windshield.

My dealership says that there is a short in the main wiring harness which costs $1200 and $500 for labor to replace. My regular mechanic has taken a look at the car 4 or 5 times now and says that although he can’t find what’s wrong but he also doesn’t think replacing the harness will solve the problem.

I would prefer not to spend $1700 but will if I can be sure the problem will be fixed.

This is not only frustrating but very, very dangerous as I end up driving when I can’t even see until I find a safe place to pull over.


A shot in the dark here. The car’s AC system has a circut to cut off the AC compressor when the car is under hard acceleration. This is make sure you have power to pass or climb a hill then the AC comes back on when you let off the gas. Have someone check out this circut for a fault.

Likely a wire is not connected and the usual place is one of the connectors themselves. Changing the wiring harness hooks and unhooks all the connectors and perhaps the problem will go away.

Tell the dealer if their work is successful you’ll pay the bill. If not, they can replace the new harness with the old one and refund your money. If they have confidence in their solution they should say OK. If they hesitate, then they don’t know what they are doing and are just gambling, they win either way. But if the harness doesn’t work you lose.

It maybe time to consider trading in the Saab.

The dealer’s mechanic is betting on the problem being somewhere in the wiring harness. And, this betting logic goes that if ALL the wiring is replaced, well, surely, the problem will be replaced. Do you want to pay for this experiment?
Further, a dealer, usually, WON’T repair, or replace, a single wire. Oh, no, let’s replace the wiring harness.
Go to a shop with specialised AC knowledge and skills, and one which isn’t afraid to repair a wire (rather, than replace a wiring harness).

As I read about the OP’s problem, I was thinking about the same possibility that Uncle Turbo talked about. The symptoms would seem to point to a fault in the circuitry that cuts out the compressor under hard acceleration, and I would suggest having this thoroughly checked prior to replacing that really expensive wiring harness.

I would think you could operate the car with a scanner hooked up and monitor if you are loosing a signal that cuts off AC compressor or a signal is generated that is cutting off Compressor. Look at BCM inputs, thats where the WOT switch reports to.

All of these sensors signals can be monitored, no need to guess. Perhaps someone needs some motivation to do better diagnosis.

Odds are that your mechanic doesn’t do air conditioners because that requires a lot of specialized equipment and complying with a bunch of environmental rules. Why not ask him if he thinks an air conditioning specialist might be better able to either get the car to work right, or install a switch that will allow you to override the normal controls and force the air conditioner to run when you want it to run? Maybe he can recommend somebody who can solve your problem without the very expensive parts hanging exercise your dealership suggests.

When you say it stops working, do you mean the A/C unit itself stops working or could you man you stop getting cool air?  You may have a vacuum problem and when the vacuum is low the blend door (that controls the air flow in the heater/AC system) and it will shut off the cool air to the cabin.

I have the same thought as JEM. If the air blend doors are controlled by vacuum then there may be a problem with the vacuum reservoir. It is there to supplement the vacuum air supply when the engine revs up and vacuum goes down. I very much doubt that this problem is going to be fixed by replacing the wire harness. How can a shorted wire problem happen when you just rev the engine? A shorted wire is going to blow a fuse most likely. If anything, I could understand a bad wire connection causing it but not a short. I’m pretty sure you will find the problem with the air blend door operation.

Joe, I would bet that you are right. I was going to suggest that myself but wanted to read the other posts first.

The air conditioner doesn’t stop completely but blows warm air instead of cold.
Thanks SO MUCH for all of the info! Most of you seem to agree on a possible solution!
I’m going to find an air conditioning specialist, any recommendations for a good one
in the Cambridge/Somerville area?

You need someone to locate a vacuum leak to the hot water valve.

Well, I guess this issue is dead by now but I still bet it is in the hot water valve. Poor vacuum.

Hello again to all of those who gave advise to me before,
This is an update and resolution of the problem I had.
I found a good Air Conditioning Specialist who spent quite a bit of time with the car late last summer and fall. he diagnosed a faulty main “monitor panel” (?) - the one the show the temp, fan level, defroster logos etc. Luckily I’d taken out an extended warranty policy and they covered a used replacement panel. (They didn’t cover a main wiring harness which is why he started looking elsewhere first.) It took 3 used replacement parts to find one that actually worked but I have had no problems since.
All in all it cost me $600 for the mechanics time and nothing for the part, although the claims specialist from the warranty company was a real jerk!