Stupid A/C question

adeihl · 12-01-2006, 08:59 AM

Hey guys,

This is my first 911. it is a black/black 85 coupe. I searched and searched but i CANT fig out how to turn the a/c compressor on/off???

I get the whole heat/defrost thing, is there a seprate control?

Andrew

Joeaksa · 12-01-2006, 09:32 AM

Should be two knobs on the console. One turns the fan on and the other is the temp control. What happens when you turn these on?

2ndTARGA · 12-01-2006, 12:01 PM

Andrew:

Here's a photo of the knobs and console Joeaksa was talking about. Hope a previous owner didn't remove the whole thing.

Ron

adeihl · 12-01-2006, 01:24 PM

i will go take a look, i dont really think anything happens. I dont notice an idle drop or anything. I have both knobs though

Thanks for the help guys,
Andrew

2ndTARGA · 01:37 PM

Hook a 12v test lamp to the hot wire that is connected to the compressor and see if it's getting power when you turn the temperature switch to full cold. If so, then your compressor or compressor clutch is the problem. If not, it's a problem with the switch, a fuse or a broken wire.

I'm not sure about the '85 system, but if all the wiring checks out you might be out of freon - most A/C systems have a low pressure cut-off that keeps the compressor from running w/o freon.

Good luck.

Ron

adeihl · 12-01-2006, 01:38 PM

I have an issue of when reving or comming to a stop, the RPM's will bounce down as far as 200RPM and then back to 800. I think the compressor is on perminantly.

Andrew

kuehl · kuehl's Garage

I searched and searched but i CANT fig out how to turn the a/c compressor on/off???
In the center console (in front of the stick) are two knobs.
Right knob turns on the a/c system and controls the three fan speeds.
Left knob controls the temperature of the evaporator coil which changes the vent temperature: turning the knob clockwise is colder, counter clockwise is warmer. Depending upon the evaporator's temperature the compressor will turn on or off.
This link explains much of what you are looking for:
http://www.griffiths.com/achelp/achelp4.html

i will go take a look, i dont really think anything happens. I dont notice an idle drop or anything.
With the engine off, open the engine deck lid and look at the compressor's clutch on the RH side of engine. A belt turns the clutch pulley. Closest to you is a hub on the clutch. When the compressor is "on" the hub should be turning with the pulley together (what a team!). So, in park, neutral, start the engine, turn the right fan speed clockwise, turn the left hand thermostat knob fully clockwise. If the evaporator's temperature is not satisfied, meaning the evaporator is above 26F-34F nominal (as explained the referenced website above) then the compressor clutch hub should be engaged with compressor clutch pulley and they are turning together.

Now whether or not the compressor is pumping, the refrigerant is flowing or the evaporator fan is blowing air out the vents is another story.

A high or low pressure switch was not stock in the 911 until the 964 came about, however some very early models may have a high temperature cut out switch attached to the drier (not common) or there could be a high/low pressure switch installed as an aftermarket improvement

Usually the RPM's are increased by the DME? when the ac is turned on (correct me experts if I'm wrong), however RPM "bouncing" could be other things (air fuel ratio "AFR") problems, bouncing air flow meter doors, air idler, etc.

Start with the suggested inspections and the follow the trouble shooting suggestions.

Let us know.