Please Help troubleshoot A/C Evaporater Blower

squelch · 06-28-2008, 02:51 PM

I recharged my A/C this morning. Everything went well and it was blowing fairly cool. I parked in my driveway to do a little more fine tuning on the A/C pressures and the blower was running just fine. I moved the temperature control knob (the one next to the A/C fan knob on the center console) and the blower just quit working. Now I can't get it to come back on. This is what I've done so far:

- Checked the 25A fuse (#2 position of the underhood fuse block).
- Jumped the evap blower motor to the battery. Works fine.
- Changed the red A/C relay on the far right of the underhood fuse block.

None of these worked. Now I'm out of ideas. PLEASE HELP. I was this close to having A/C.

Thanks,
Chuck

Hugh R · 06-28-2008, 02:59 PM

Try bypassing the thermostat in the back. Be careful pulling it out, you can break the little temp sensor tube. Also check the 3 position switch, it carries a lot of load. Mine burned out and I bought a brand new one, not Porsche, but works just fine for $10 at an auto A/C supply.

squelch · 06-28-2008, 03:32 PM

Thanks for the input Hugh. I forgot to mention that I had also tried:

- Disconnecting the two green wires from the back of the thermostat and touching them together. Don't know if that is what you mean by bypassing the thermostat, but that is what I tried.
- I also used a circuit test light and touched each pin on the back of the fan switch. Did not get a light from any of them. That sounds like it might be a bad switch, but I'm not a great troubleshooter when it comes to electricity.

Thanks,
Chuck

Jim727 · 06:20 PM

Have you checked the fuse on the relay in the smuggler's box? On mine, there's a Wehrle relay in there with (I think) a 15A fuse. When it blows your evaporator blower will quit and the front condenser blower will also quit. This fuse carries the load for the evap blower, the compressor clutch, and the control circuit for the front condenser blower relay. If you run the evap blower full speed you can feel the fuse get hot.

This last week I cleaned up all the contacts and added another relay (got a Wehrle from our host and changed the new fuse to 3A) to support the compressor clutch load. Left the fuse in the smuggler's box unchanged. Now the smuggler's box relay fuse carries the load for the evap blower, the control circuit for the compressor clutch relay, and the control circuit for the front condenser blower relay. Seems to have helped as my smuggler's box fuse runs cooler now.

Relay: http://www.pelicanparts.com/cgi-bin/ksearch/PEL_search.cgi?command=show_part_page&please_wait=N&make=POR&model=911E&section=VENTac&page=2&bookmark=10&part_number=911-615-103-01-M206

Also, there is a factory update to put an inline fuse to the front blower motor - highly recommended if your model doesn't have one.

squelch · 08:37 PM

Jim,
I checked the fuse in the smuggler's box. I didn't know about that one. It was old and discolored, but not blown. I replaced it anyway. The evap blower, the front condenser blower and the compressor clutch still don't operate.

This all occurred immediately when I adjusted the temperature on the thermostat knob to a warmer setting. Any ideas how that thermostat knob could effect the circuit? Any other fuses or relays that I should know about. If the fan switch is bad, I assume that would prevent the evap blower, front condenser blower and compressor from coming on. Can someone walk me through how to test that thing?

Thanks,
Chuck

Hugh R · 06-28-2008, 08:56 PM

On the fan switch, don't use a continuity tester, use the volt meter part of it. check for voltage in and out. You should pretty easily figure out voltage from the incoming line and a good ground, like any piece of metal on the body of the car. I'll bet your fan speed switch took a dump.

Jim727 · 06-29-2008, 12:25 AM

Did you check to see if the relay in the smuggler's box is activating? The symptoms you describe sound like power is not getting from the relay in the smuggler's box. That could be due to relay failure, failure of the fan switch as Hugh suggests, or possibly separation at one of the connectors.

As I recall, the fan switch energizes the system and the thermostat controls when the clutch engages. The first thing I would do is: with the engine and a/c off, turn the ignition switch to on but don't start the engine. Turn the fan switch on and off - you should hear fans and the compressor clutch responding. If you get nothing, check the relay in the smuggler's box for power at the control circuit and at the input to the power side of the relay. At least now you will know which side of the relay the problem is on.

If your fan switch gave up, seriously consider the Griffiths continuously variable fan speed switch. It's infinitely better than the stock switch.

For troubleshooting, this should help: http://www.griffiths.com/achelp/achelp2.html

Griff (Kuehl) may check this thread and have some input for you here as well.

squelch · 07:56 AM

Well gents, I got it working... but I don't know how.

I first jumped the A/C relay to the battery to see if it was working, and it was. All of the blowers and the clutch came on, which indicated that the relay was fine.

I then tried measuring the voltage on the wires going into the switch. In the off position, the red wire had 12V, but when I turned the knob to any other position on the switch, all of the wires, including the red one that had 12V, had 0V and the fans did not come on.

I tried to bypass the switch by jumping the red 12V to the other wires on the switch positions, but this did not do anything.

So I thought that power might not be getting to the temperature switch, causing a relay not to close (This part was a little fuzzy for me as I tried to decipher the wiring schematic). So I jumped directly from the hot wire to the green wire going to the relay, thus bypassing the temperature switch. This didn't work either.

So I second guessed my thinking and went to re-jump the A/C relay to the battery to start over. When the fans didn't come on, I remembered that the blower switch was not on, so I disconnected that jumper and went to turn the blower on and everything worked. Now that it works, I get positive voltage at each position on the switch. Intermittent switch maybe?

Everything is in the same position as it was when it failed yesterday, so I don't know what happened or what I did to fix it. Any thoughts would be appreciated in case it fails again. I'm kind of leaning towards a bad switch still.

Anyhow, thank you very much for your insight on this system. There are still a few things that are a little fuzzy to me, but both or your inputs gave me a much better understanding about how the system works and how to troubleshoot electrical components.

Does anyone know a good source for an OEM blower switch? As much as I would love to replace the switch with the $300 one from Griffiths, I'm not quite ready to do that until I get my A/C working well.

Thanks again for the help,
Chuck

squelch · 06-29-2008, 12:01 PM

Took the car for a drive to test my new A/C. Fan was working fine for about 30 min. Went into a store. When I came back out and cranked it up... No more A/C blower.

Put the voltmeter on the red wire on the switch. It reads 12V with switch off.
When I turn the fan switch to any other of the three fan speeds I get 0V on the previously hot wire. I don't know if that is normal, or why it does that. I would think the hot wire would always be hot, regardless of switch position.
Suggestions??

Thanks,
Chuck