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air conditioning cuts out


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:o My 97 STS has about 180,000 miles on it and runs great. The other day I was driving on the highway and the fan kept cutting out when I went up hills. It was a very hot and humid day about 90 f. It has been giving me trouble from time to time. It was worst than ever the other day though. It somtimes sounds like a jake brake on a truck, which I think is the valve in the heater box vibrating. I have checked for a vacuum leak but have found none. The tank does not have a leak in it and the check valve is good. I have check the system over with a vacuum gauge. I have a feeling it is the rings. Does anyone have any ideas. thanks Dan
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Does the HVAC blower motor actually stop - or do you mean that the air doors are moving and the blower noise subsides for a bit?

If yes to the above query, then it seems that the vehicle still has a vac leak of some sort, but you have not found it yet. As you pointed out, when going up hills or at other loads - the throttle plate position changes - so the engine vac changes and the problem is precipitated.

I would "tee" in a small vac gage into one of the vac hoses the under the dash going to the HVAC ductwork. Basically, watch the needle when the air doors of the HVAC change position unexpectedly. This should verify that the problem is vac or mechanical (not the control system messing up).

If you think the control system might be changing the air door position, you can enter the diagnostic mode via the instrument panel and set the air doors to whatever. Search for codes and diagnostics on this site to find out how to do this for you model year (hopefully the right area can still be accessed on a '97).

The "jake brake" noise you hear is still only around the HVAC area right? Perhaps the air-motor or diaphragm (that the vac moves) - has a leak at a certain point or the linkage is messed up.

I'm not sure what you mean by "rings" Surely you are not referring to the engine's piston rings being worn are you? Even if this were true, (which is doubtful) it would not explain the air duct problem. If engine vac were that poor - the engine would simply not operate (the HVAC would be the least of your problems).

You have probably thought of most of the above, but perhaps one of the site's Gurus will respond with some better ideas.

Good Luck :)

Add power to leave problems behind. Most braking is just - poor planning.
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thanks for the reply TDK. I am still looking for the vacuum leak but not having any luck. I checked at the solinoid pack / manifold and all the plumbing and vacuum actuators in the car. I have to wait not until a hot and humid day and traveling on the highway with a long hill.

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