Engine idle drops with A/C
 

Hi All

I noticed a strange problem when I operate my air conditioning in the car.
When I operate it, the engine idle drops. it even worse when the head lights are on.
I know that there should be some vacuum unit that controls the idle level but I dont know where it is...or maybe the problem is somewhere else? :confused:

Can somebody help me with this issue?

Thanks.

A/C units area huge bog on the engine. This is why you get better gas mileage with it off. There are lots of vac units behind the HVAC controls if you want to know where they are. You should only hear them woosh when they move a lever, but should stop after that. If it's continuous vacuum noise, then you probably got a leak.

Thanks, the units should physically move the throttle a little bit? or they just "pump" air into the engine to make the idle higher?
Those vacuum units are in the engine area? or inside the car?

Depending on the year of your car, there's most likely a valve that's designed to allow more air to the intake when the AC is turned on, thereby increasing idle speed and avoiding the drop you speak of. My 78 does not have one but most cars I've seen do have the valve and hoses attached to the crossbar. I'm really not familiar with troubleshooting them though. It would help if you'd give some details about the year of your car.

As for the idle dropping when the headlights are on, this could probably be solved by cleaning the electrical connections at the battery, starter and jump post as well as your ground points.

Yes, Stephen is correct. I forgot about the piece that hangs from the crossbar. Yes, this is a switch that opens (air) to increase the idle higher when the A/C is kicked on. You could probably test that this is getting voltage when the A/C is on and off. Those HVAC vacuum solenoids are in the center console. Also probably depending on what year. I have an OB so that's where mine are.

What year is your car?

The later cars have a signal feed to the LH ecu that tells it when the AC compressor is engaged and compensates the idle. Its one of the standard actuator tests for the ecu diagnostics devices (Bosch Hammer or equivalent)

I am sorry, the car is from 1980.
Is there a way to check this unit that hangs of the crossbar? or the only check is to see if it gets 12V when opening the A/C?

Check for 12v when its supposed to be working, and you could also pinch one of the hoses either coming or going from it to see if the idle speed changes when its supposed to be open.

Thanks, I will try to check in the following days!

Was that electric air valve retrofitted to some older cars?

My 79 doesn't have it, but I have seen pictures of 78/79's with the valve.

Some early and Euro cars didn't have factory AC.

Do you have a couple wires unattached from the front harness?

Maybe check PET6?

Hey Raymond,

If you feel left out by not having one of those hanging from your crossbar, I can make one out Bondo and Silver Paint it and a couple wires and presto! SmileWavy

That's odd because my car has factory AC, yet no valve and no sign on the crossbar that a valve was ever mounted there or any unexplained wires. Keep in mind I've never actually gotten the AC to work and that the compressor and hoses are now in a box in the garage.

The aluminum crossbar I got off of ebay did come with a valve but I may have thrown it out.

Only if it has some kind of vortex generator built into it so that improve power and gas mileage! :D

No evidence of my car ever having had one, no loose wires.

Wonder if it wasn't specific or added on to cars with auto trans in order to help them idle in gear with the A/C on?

Can you (or anybody) please tell me if this valve has a Porsche part number? mine is very weird (no numbers) and doesnt do anything so I thought of buying a new one...I still don't understand if this is something that was originally made or was added later :confused:

I am sure 928 Intl would have a good used one with a warranty. Or you can get a 2nd mortgage on the house and buy new.

Dont want to take a 2nd mortgage :(... I didnt find this part in their web site...do you know the part's name?

928-606-215-01 $111 for the Porsche part here on Pelican.

Thanks!

Mike is a PET Guru!