AC switch non-functioning...

[andyt11]

After winter hibernation, my AC switch (right hand rotary in the center console) does nothing. It doesn't make fans run. Nothing happens at all.

Ive been short on time, so all I've done so far is:

• check fuses
• check I have 12v at the red pin 30 at the relay in the smugglers box
• check the relay operates when I provide 12v across pins 85 and 86

Any suggestions on how to proceed. The bentley diagram for an 88 911 is ludicrously complex and I cannot follow it. (although I have to admit, electrics are not my strong point)

Also, and likely not related, three of the four electric seat switches are now dead. One operates fine though. But I only mention that in case it could be relevant. My main concern is getting the AC back.

[DRACO A5OG]

How is the refrigerant level? if low it will not kick the compressor on. So I assume compressor is not engaging as well?

[andyt11]

I just thought of that. I'll check tonight. Thankyou.

[DRACO A5OG]

Keep the dial on the lowest ( Hottest ) setting and have a helper turn the dial to max and see if compressor kicks in.

[Discseven]

Andy... here's AC wiring diagram. Perhaps simpler than Bentley's. It's been a while since I solved a myriad of issues with my AC so I can't recall what would shut the fan down completely. I'm thinking it may be the thermo (temp) switch because I marked a bypass on my diagram to test that switch. If you have power every where and you're 100% sure relay in smuggler's is working correctly... it may well be the thermo switch. Bypassing it will resolve that question.

EDIT: Refer to Kuehl's input rather than mine.

[kuehl]

Andy,

1) Check fuse on in front trunk on fuse panel, AND check the wire leading out for corrosion

Ign key on accessory position:
2) Relay in smugglers box, check for power to terminal 30, then check for power
coming out of 87, if all that is good:

3) Locate power wire to evap blower motor, disconnect, check for power in the power connector going to the blower motor (females spades on molex connector); red wire; check all 3 fan speeds. If you have power it's the evap blower motor, if you don't have power:

4) Under the RH passg foot board, remove board, locate the black plastic trapezoid, there is fan speed control (spring resistors and overheating point set).
Unplug the square black electrical plug. Inside there round pins and wire colors are typically Red/Green for low speed, Red/Black for medium speed, Red White for full fan speed. Check each wire's plug connector. If no power at any or few its the fan speed switch; Pelican sells it 911-613-243-00. If you are getting power at the plug check the thermal "point set" to see if contacts are making or open.

[86 911 Targa]

^^^^^
Here is the factory manual for the 3.2 A/C.

^^^^^
And the fuse panel showing that fuse #2 is common
to both the A/C and the power seats.


^^^^
Fuse #2 carries a very high current load.

You could read 12v at the fuse, but under load
a series resistance issue could drop that voltage.

Suggestion:
1. Remove fuse #2, and, check for voltage at
the TOP of the fuse holder.

2. Clean the fuse holder, and install a new fuse,
and remove the bottom red wire that feeds the AC.

3. Try your seats again.

I think you may have some type of failure either at the fuse
holder, or, one of the wires at the bottom of the fuse holder.

Also, check the green wire at the compressor.

pm me as needed.

Good luck,

Gerry

[kuehl]

He said the evap blower motor was not working, the issue is in the front section of the circuit.

Depending upon the year of the car with electric seats, when the seat motor or switch goes south that can blow the AC fuse, however his is intact.

[andyt11]

Thank-you so much for all the excellent info. I'll work through it and report back.

Kuehl, point 3 of your post, is the evap blower the one blower in the smugglers box?

(I've never known a car with more fans and blowers in my life!)

[Hugh R]

If the rotary console switch is bad, like mine was, you can bring the old one to an A/C supply and get a new one for about $20.

[kuehl]

Andy.....yup

[andyt11]

Ok. So I checked and cleaned the fuse thoroughly. All is well. I probed the socket with the relay in the smugglers box, and with the ignition on, I have 12v at pin 86, but not at pin 87. I checked for 12v at pin 30 but there is nothing, which explains why there is nothing at pin 87.

I removed the relay and now I have 12v on the terminal that would connect to pin 30. As soon as I put the relay back in, I get zero there.

The relay clicks when the ignition is switched on and off. A replacement (not guaranteed good) relay behaved exactly the same way.

So what's happening to my 12v on pin 30 when the relay is installed?

[andyt11]

Just tried a third, known good relay. It functions the same as the other two.

[86 911 Targa]

Originally Posted by andyt11

Just tried a third, known good relay. It functions the same as the other two.

Andy,

You may be missing the 12v from the compressor as previously mentioned
in one of my posts.

That connector at the compressor in the engine compartment is exposed
to a lot of contamination.

1. Open up/clean the connector.

2. If that does not help, place 12v (fused) on the green wire going to the relay
pin #86 as per my jpg.

3. If the relay pulls up, then, place a ground on the other side of the connector
to the compressor with the connector disconnected.

4. Let's see if that engages the compressor clutch.

5. All of the above with the ignition "ON".

6. The yellow wire to pin#85 is from the ignition switch.

Your M/Y 88 should be very close to our M/Y 86 CKT.

Gerry

[kuehl]

Andy,
I forget whether or not the power is cut to the relay when the starter is engaged.
Test the relay again but with the engine running.

"Normally", when the ign key is in accessory position or engine is running
and your turn on the evap fan speed switch to either of its 3 speeds, the evaporator
blower motor will run. And, if the ac thermostat contacts are making (closed)
calling for demand the front condenser blower motor will run and the compressor
clutch will engage (to test the later 2 set the thermostat fully CW to the right).
However, if you don't have power going to the evap fan speed switch the thermostat
won't get power either.

Focus on getting power out the primary AC relay in the smugglers box, as a test
you could by pass it (I believe solid red provides power to the evap fan speed
switch). Wire colors at the AC relay might be different depending upon
the year however pin functions should be the same.

[andyt11]

Kuehl

Normally, I'd expect the blower to run with the key in the accessory position. Wouldn't normally need to run the engine, but I'll check with the engine on too.

As for bypassing the relay, I guess I could just remove the relay and jumper the plug that goes on to the relay. Put 12v from pin 30 direct to pin 87, as if the relay was doing that for me right?

Then I'd expect the blower to run.

The bit I really don't understand is that I have 12v on the terminal that connects to pin 30, but if I plug in a relay it goes away.



86 Targa,

I'll check the plug at the back of the car and clean it up. After that I'm afraid I'm not following you (which is my fault, I'm not an electrical wizard)

Your diagram has two a/c relays which is confusing me.

And I already have 12v at pin 86.

And the relay does pull when the ignition is turned from off to accessory.

Will investigate further and report back. Thank you all, its a huge help.

PS - electric seat issue doesn't appear to be related. I dissembled and cleaned one of the non functioning switches last night and have got it working. I suspect they just packed up at the same time.

[kuehl]

Originally Posted by andyt11

Kuehl

Normally, I'd expect the blower to run with the key in the accessory position. Wouldn't normally need to run the engine, but I'll check with the engine on too.

Yup. However (and I"m no expert either, lol), I recall something some time ago when an owner had a starter wiring issue and it was interfering with what you normally expect to happen...... when key is in accessory the coil in the relay pulls in the contacts and current flows from 30 to 87, crank the engine and the coil breaks the contacts (or visa versa, lol). However, if you have swapped out 3 relays and they have the proper design (SPDT?) I'd suspect the funky starter or wiring issue.

Originally Posted by andyt11

As for bypassing the relay, I guess I could just remove the relay and jumper the plug that goes on to the relay. Put 12v from pin 30 direct to pin 87, as if the relay was doing that for me right?

Sure. Pull the relay and jumper 30 wire to 87 wire and test evap fan speed switch.

Originally Posted by andyt11

The bit I really don't understand is that I have 12v on the terminal that connects to pin 30, but if I plug in a relay it goes away.

Yah, funky. I'm still on coffee number 1 this morning. Maybe Gerry can explain how the circuit (relay) works with the starter system.

[andyt11]

Perhaps I have 12v on that terminal that connects to pin 30, but no amps.

I'm going to try putting 12v directly from the battery to the terminal on the socket that normally connects to pin 87. That should allow the fan to run. Perhaps while the fuse tests good for continuity, I'm not getting any current.

[kuehl]

Not a common problem but go for it

[86 911 Targa]

Good to hear that the seats are working!

I thought that the two issues might have been mutually inclusive.

Now we can now chase down the last issue.


^^^^^

1. There are two A/C associated relays in your car.



^^^^^
One is the relay located in the "smuggler's" box
which I call the evaporator relay.

It's the one with the yellow wire on the CKT diagram.


^^^^^
And, the relay located on the fuse panel in the "frunk"
which I call the front condenser relay.

The condenser relay is the one on the left side on the CKT.
And, the evaporator relay in the one on the right side adjacent to
the condenser relay with the yellow (GE) wire.

As I understand your issue, there is 12v on the evaporator relay pin #30
until you plug the relay into the socket. Right?

Let's start from there.

Gerry