A/c fan goes off when you accellerate

LizaKiesling · Post by **LizaKiesling** » 13 Jun 2005, 21:00

88 760 w/ turbo. I have had this car to an ac shop and they have not been able to solve the problem. I have seen in the past that when the 760 has a problem it usually is not an isolated incident. Has anyone fought this battle and won yet?? Does anyone have any EASY answers? Thanks. Liza Kiesling.

yeagermeister · Post by **yeagermeister** » 14 Jun 2005, 05:55

as i understand it, when the turbo kicks in the a/c compressor turns off, freeing up the engine to do what it's supposed to do, with no stress from the compressor.

LizaKiesling · Post by **LizaKiesling** » 14 Jun 2005, 11:33

I have had another car with turbo and you didn't spend lots of time with the a/c off every time you pressed on the gas. The car is hot the a/c fan is not running anytime you are actively pressing on the gas. i don't think it is normal. i was trying to sell the car at one time and someone else mentioned it also. Liza

Kmaniac in California USA · Post by **Kmaniac in California USA** » 14 Jun 2005, 14:42

When you say the A/C fan shuts off on acceleration do you mean that the blower motor turns off, just like turning your fan switch to 0, or air stops blowing out the dash vents, but could be redirected to other vents, like the defroster? To double check this, turn your fan on high (max or 4) when you take a drive. At this setting, you can hear the fan motor and will know for sure whether it is running or not. Then, during acceleration, put our hand both above and below the dash to check for air flow from the defroster and floor vents.

I know in my 1986 740 GLE (no turbo) that when I accelerate, the drop in engine manifold vacuum causes my vent dampers to readjust to defrost mode until I let up on the throttle. Then the air flows back through the dash vents, again. When I use my A/C through the dash vents, cold air blows on my face. Then, when the air redirects on acceleration, my face begins to feel abnormally warm with the sudden loss of cold air blowing on it. This could leave one with the false sense that the A/C has shut off or blowing warm air when it has merely redirected the air through other vent outlets.

It has been my experience with other cars that heavy or full throttle acceleration may automatically disconnect the A/C compressor clutch to temporarily remove this load during acceleration. If your car is set up this way, it should have no effect on the blower fan inside the car. You may feel a slow increase in discharged air temperature until you let up on the throttle, but that's it.

Take another look at this again and let us know what you find. I also suggest you search this forum on key word "kmaniac" to view my other posts on this subject.

LizaKiesling · Post by **LizaKiesling** » 14 Jun 2005, 14:47

Thank-you, I will try what you suggested. Liza K.

irby · Post by **irby** » 21 Jul 2005, 18:43

My experience with this condition:
-- not only on acceleration, but anytime the vacuum is reduced, like hill climbing, etc. Dealer said that the air motor that controls the dash dampers partially failed, and it was expensive! This happened again a few months later, and they said that another air motor was at fault--this one was NOT fixed.
I switched the a/c fan from automatic to manual and sometimes the air flow is not interrupted, but other times it stops!!
I would like to block the air dampers open, but think it might be too big a job.
Comments??

jackwk · Post by **jackwk** » 28 Jul 2005, 09:43

I have the same issue with my '91 940 turbo. I agree that it is a loss of vac from manifold. I'm also investigating vac leaks to the air motor. I guess the motor diaphram could partially work but be leaky. On my car air routing flips-out all the time, I hope I don't have to replace air motors. How expensive are they?

thanks,
Jack

irby · Post by **irby** » 01 Aug 2005, 10:19

As I recall, the cost was at least $250.

Kmaniac in California USA · Post by **Kmaniac in California USA** » 01 Aug 2005, 12:51

To those of you suffering from redirection of A/C air flow on acceleration:

It is easy to think that the A/C is shutting off on acceleration, especially when you have set your A/C to Maximum or Recirculate. When the vacuum leaks off, the controls default to the Defroster setting, which redirects air flow to the defroster vents and opens the fresh air door, forcing the system to cool warner, outside air. The loss of cold air blowing on you and the sudden increase in temperature of the discharge air can fool you into thinking the A/C shut down. Here are some tips to help diagnose the problems with your car should you experience this condition.

One thing you should do is check the integrity of your vacuum reservoir tank under the car. Small cracks in the tank can cause variable vacuum. This tank is positioned under the car in front of the cross member. This tank is the first thing under the car to receive blunt force trauma if you run over something, so they are prone to road debris damage.

Another thing to do is check the integrity of the large vacuum hose between the intake manifold and the vacuum tank. Rubber hoses age and crack over time. Deteriorated hoses will leak and not hold vacuum. You will also find a vacuum check valve between the intake manifold and the Vent Control Tee fitting. Check the integrity of this valve, as well. Replace any leaking or questionable hoses.

To check the integrity of your vacuum motors (in the dash), obtain a hand-held vacuum pump. You can get one at most auto parts stores for less than $20, or you can borrow one from a friend. Disconnect the Vent Control vacuum line at the tee and connect the vacuum pump to this line. Set your vent controls to a position at one end of the panel and draw a vacuum in the line to 20-25 inches of Hg. If the vacuum in the line remains constant, your vacuum motors for that circuit are intact. Should the vacuum leak off at any rate, one of the vacuum motors for that circuit is leaking. Repeat this procedure for each setting on the vent controls and note what happens at each setting. If you cannot hold a vacuum in any setting, you could have leaks in your supply line to the controller or the controller itself.

Trouble shooting of this system is best performed starting at the dash controls and working your vay back to the intake manifold.

Jack · Post by **Jack** » 12 Aug 2005, 13:25

Chris and all,

Thanks for your help. I fixed my 940se using your advice. I also had the air motors directing treated air into "no man's land" when the engine was loaded causing a loss of vaccume. I replace all the original vac lines and put a cap on a barbed fitting that was sticking through the firewall where the AC stuff enters the passenger compartment. I'm not sure what specifically got the vaccume up because most of the lines were pretty rough and the fitting just looked wrong. This is the best way to approach the problem, it sure beats digging into the dash. The vaccume line that enters the drivers compartment that should hold a vaccume never held a vaccume. I may still have a leaky vac motor but it has been working for over a week.

best of luck,

Jack