A/C Not Working :(

Kamoman · 06-10-2010, 01:46 PM

The A/C in my '83 911 SC is working. How timely for this hot & humid Houston heat! I was having the system charged up and the mechanic said that the compressor was not getting power? He checked it and it is good as it was replaced last summer. The blower comes on and works however last year, it would periodically not blow. I would fiddle with it then it would come on. They checked my fuses/relays and said they were also good. One guy seemed to think that it could be the Evaporator Temperature Sensor??? They estimated this to be a $400-$500 job to track, replace and service the system. Ouch!!! This is not my daily driver so I'm looking for help here.

Thanks!

86 911 Targa · 06-10-2010, 02:14 PM

Quote:

Originally Posted by Kamoman

The A/C in my '83 911 SC is working. How timely for this hot & humid Houston heat! I was having the system charged up and the mechanic said that the compressor was not getting power? He checked it and it is good as it was replaced last summer. The blower comes on and works however last year, it would periodically not blow. I would fiddle with it then it would come on. They checked my fuses/relays and said they were also good. One guy seemed to think that it could be the Evaporator Temperature Sensor??? They estimated this to be a $400-$500 job to track, replace and service the system. Ouch!!! This is not my daily driver so I'm looking for help here.

Thanks!

pm me.

Barrpete · 06-10-2010, 02:46 PM

Was your mechanic familiar with 911's? The relay in the smugglers box often gets overlooked.

You can easily check the evaporator temperature sensor. It's part of the temperature switch. The one on the left of the center console. It has a white tube that comes out the rear of the swith and goes thru the firewall into the evaporator. The tube is filled with an inert gas that expands/contracts with temperature opening and closing the contacts inside the switch. It's designed to shut off the compressor below a certain temp so your evaporator doesn't ice up. If that tube has cracked and the inert gas has leaked out the switch contacts will open up and your compressor clutch won't engage. The other thing that can happen is the contacts get dirty which will also prevent the compress clutch from engaging. It's easy to check, just remove the switch from the console and bypass it. If the clutch engages then the switch is either bad or dirty. Then you can either clean or replace it.

86 911 Targa · 06-10-2010, 05:13 PM

+1, However, replacing the temp switch has become a bit of an issue as the factory and aftermarket switches will not fit in the console as did the original switches.

Also, (and I've done this twice on our '86), it can be a delicate operation as
the capillary tube is prone to damage during installation, and must be properly installed in the evaporator.

Additionally, the switch, if not allready properly adjusted, should be adjusted for a 38F compressor shut-off with an operating window of 40F off, 50F on, thus precluding evaporator freeze-up.

I can send you pics on how I adjusted the switch on our '86 along with the results.

Good luck,

Gerry

Barrpete · 06-11-2010, 06:38 AM

That's why I ended up cleaning my original switch. When mine went bad a few years ago I searched in vain for a replacement. Cleaning it was actually pretty simple, there is a plastic panel that you can carefully slide off to access the contacts. After 25 years that switch was pretty full of dust and crud but it cleaned up real easily with electrical contact cleaner and works fine now.

+1 on the delicate nature of the capilly tube. Any kinks or breaks and the switch is useless.

I wish I'd known about the temperature window adjustment when I had it out. Oh, well I guess that will have to wait until the next time it needs to come out.

Tim Hancock · 06-11-2010, 08:08 AM

My fuse block in my '79 SC was what was causing a similar problem for me (fan/AC cutting off randomly). I ended up tearing it apart and swapped the wires to an unused fuse block.

Hugh R · 06-11-2010, 08:39 AM

If the temp sensor is shot and you don't want to spend the $$$ put a jumper wire across the switch, it will run and not cycle, but it will run. $300 to $400 sounds like an awful lot for that item.

86 911 Targa · 12:36 PM

Quote:

Originally Posted by Tim Hancock

My fuse block in my '79 SC was what was causing a similar problem for me (fan/AC cutting off randomly). I ended up tearing it apart and swapped the wires to an unused fuse block.

Tim,

We went through the very same issues on our '86.

Fuse #2 always ran very hot, causing the A/C to fail.

One of the more common reasons for this type of anomoly, is a
series resistance in the circuit due to corroded relay contacts,
and/or the early Porsche bullet aluminum fuses with copper contacts,
which were prone to corrosion due to high current and moisture.

I checked the current draw at both the condenser fan (4.8A), and,
the evaporator fan (7.2A @ the highest fan switch setting).

Here is what I did.

The front condenser fan (fuse #3), is now fused separately from the evaporator(fuse #2).

Fuse #3 is dedicated to the Cabriolet convertible folding top, (which, we do not have), and the headlight washer.

Mike Andrew · 06-14-2010, 09:20 AM

subbed.

Tim Hancock · 06-14-2010, 09:35 AM

[QUOTE=86 911 Targa;5399688]Tim,

We went through the very same issues on our '86.

Fuse #2 always ran very hot, causing the A/C to fail.

One of the more common reasons for this type of anomoly, is a
series resistance in the circuit due to corroded relay contacts,
and/or the early Porsche bullet aluminum fuses with copper contacts,
which were prone to corrosion due to high current and moisture.

I checked the current draw at both the condenser fan (4.8A), and,
the evaporator fan (7.2A @ the highest fan switch setting).

Here is what I did.

The front condenser fan (fuse #3), is now fused separately from the evaporator(fuse #2).

Fuse #3 is dedicated to the Cabriolet convertible folding top, (which, we do not have), and the headlight washer.

[QUOTE]

Yeah my fuses were getting scorched and the contact points would look like they were corroded/burnt due to the heat eminating from the poor connection at the back side of the fuse block body. The fuses would change color from the heat yet they were not blowing from an overcurrent condition. I do not recall exactly what empty fuse holder I switched to, but ever since I did it, my fuse stays cool and the AC no longer cuts out. The back of the original fuse holder was in pretty miserable shape even though it looked OK from the top. The problem was the rivet/staked joint on the back side.