A/C Not Working

[kevinb34322]

So it's getting to the time of year where this is going to be a concern soon, but the A/C in my 86' 911 doesn't appear to be turning the compressor on to blow cold air. All of the fans work and it will blow air. I know the relays on these cars tend to be the culprit, but I wanted to see if there was any advice out there on where to start with going through these to check and if a regular multimeter will be able to show me which relay is the culprit rather than just starting to replace them.

[DRACO A5OG]

all the fans? there is only one. Which fans are you writing about?

Please post a pic.

There should only be two dials, one for temperature and the other for speed. I assume you turn the temp dial all the way to the right and speed to max and then checked the compressor?

What is the ambient temps when you tried to use it?

[kevinb34322]

Sorry about that, I mispoke with "all the fans". When I turn the knob for the fan it blows, just does not get cold.

The compressor clutch does not appear to be engaging when I have it set to the coldest setting, leading me to believe it must be a relay somewhere between the switch and the compressor. I have not checked the voltage readings at the compressor side yet (or anywhere for that matter). I'm just looking for suggestions on where to start that may be a common failure.

The ambient temperature was in the low to mid 70's

[86 911 Targa]

There are two A/C relays:

1. The front relay on the frunk fuse panel.
2. The other in the smuggler's box.
3. Also, the console mounted temperature switch capillary tube.
4. Fuse #2 on the fuse panel.

Also, other issues should be evaluated.

You may pm me as needed.

Good luck,

Gerry


^^^^^
Smuggler's box relay.



^^^^^
Console mounted switch.

^^^^^
Fuse panel A/C relay.

[GH85Carrera]

Put a volt meter on the wire connector to the compressor. If there is not 12 volts present when the AC is on, you know it is some connection or relay. Disconnect the wire and put 12 volts right on the connector. Does the clutch engage? If it does the compressor clutch is not the issue.

Now you can check the relays and fuses.

[911tracker85]

if low on refrigerant, the compressor will not engage. there is a sensor to detect for proper system pressure to prevent the compressor from running when low and burning it up.

even if you check one of the shrader valves and get some coolant to come out does not mean there is enough refrigerant for adequate systems pressure. if you check an no coolant.... there's your sign.

dont recall where that sensor is, but think if you find it and jumper it that would fake out a low refrigerant reading. I think..... been quite a while since I worked on AC on a 911.

[yellowperil]

when the a/c on my '86 quit, I fixed it by replacing the relay in the smugglers box. Very simple.

[GH85Carrera]

Originally Posted by 911tracker85

if low on refrigerant, the compressor will not engage. there is a sensor to detect for proper system pressure to prevent the compressor from running when low and burning it up.

even if you check one of the shrader valves and get some coolant to come out does not mean there is enough refrigerant for adequate systems pressure. if you check an no coolant.... there's your sign.

dont recall where that sensor is, but think if you find it and jumper it that would fake out a low refrigerant reading. I think..... been quite a while since I worked on AC on a 911.

Unless someone added a sensor to the system, there is not one. Porsche did not have a sensor at all for low or high pressure on the compressor as delivered from the factory.

When I upgraded my system to the Griffiths technology Mr Ice project part of the upgrade is a sensor.

The quick easy test to see if the compressor clutch works it just put 12 volts to it. If the clutch snaps closed it is working. Now you need to find out what it is not getting the 12 volt signal.

[stormcrow]

Kevin,

Check to see if the compressor is turning. If it is not then pyll the wire off the conpressor and check to see if you are getting 12V. If not then the temperature controller is the problem.

If the compressor is working then the problem is low refrigerant. And a refrigerant leak.

[911tracker85]

Porsche did not have a sensor at all for low or high pressure on the compressor

interesting.... was not yet into serious wrenching when I pulled the AC out of the 911. so never checked.

but since then have rebuilt AC on 944s and a 928, they all have sensors, 86, 87, and 84.

[GH85Carrera]

944s and 928 were designed from the start with an AC system.

The AC system for the 911 was cobbled together from the factory and it is just an add on system.

I don't know for sure but I suspect few if any other cars have completely separate and independent heating, air conditioning and fresh air systems. How many other cars with "factory AC" can run the AC and the heater and the fresh air at the same time?

Look at the wiper delay system. A little tiny knob on the dash that once again is completely separate from the wiper controls.

There is no fuse for the front condenser motor as delivered from the factory. It is an pure add on bodge. The missing fuse caused many 911s to burn to the ground. If your car does not have one, add one NOW!

The AC system is rather anemic at best as delivered. It can be made to work great and mine will keep me cool in August in Savannah, GA or in 105 degree heat of Needles, CA.