wds928

My 94 GTS is giving me fits with the cooling fans (two electric), the A/C and such.

Fan Controller(beneath cover btwn door and passenger seat) has 7+ volts from pins 6 and 8 with the A/C button pressed SOMETIMES, usually first thing in the morning. The A/C and cooling fans work fine when I have more than 7 volts at these pins, as per the WSM, Page 19-25, Volumn 1 (88+ MY)

I drive to town, stop the engine for a while, come back, start the car and NO A/C (button does not light up, compressor doesn't engage), no cooling fans. I check the voltage and it's down to less than 0.05 volts at pins 6 and 8. Pin 2 ov connector has battery voltage.

I test pin 4 (page 19-22) and get only 0.01 volts, instead of battery voltage of 12.5+.

I test the AC button on connector II at pin 5 and get 0.0 voltage.

Something's not working correctly.

The hood switch is new (ok, last fall). The a/c head unit is replaced with the Radio Shack unit.

Is it the A/C button or the fan controller itself?

When the fan controller has less than 7 volts, the fog lights also don't work.

The fan controller is a safety feature to keep the a/c from working if the cooling fans don't work. I'm stumped. It works sometimes, but not others, usually after it has worked.


Wally, anyone have a suggestion?

MikeN

How do the fans act without any A/C usage? Do they cycle properly as would be the normal operation? If they do than my guess would be that something is not telling the fan controller that the A/C is "on" and therefore the fans don't run when the A/C button is pressed. Does the A/C suddenly start working when normal cycling of the fans begins with the engine warmed up? With the new head unit relay installed have the fans ever run correctly to your knowledge?

I guess I've been lucky, never had any problems with this system on mine so don't know it in depth, but the fans should be running pretty much all the time with the A/C on........and if they aren't then something is not telling the fan controller the A/C is on, or the controller is not operating correctly if the A/C signal is received.......nothing that you probably don't already know.

wds928

Mike, the cooling fans don't work, but only intermittently. My problem seem sto be that after running the car a bit, then stopping, the cooling fans stop working, evidenced by rising temperature during stops and no fan noise from the engine compartment.

The lack of cooling fans, I believe is the cause for the A/C to not work, not the other way around. The whole system has worked fine for most of last summer and fall, but only this spring has the problem come back. Initially, it was just the battery terminals (or so I thought).

I'm going to check the intake temp. switch ohms this morning before going to work.

Thanks for the input.

doug928

Bill,

Check the fan fuses - even if they appear to be good replace them with new. I had a similar problem where the fuses were good but had just enough oxidation on them that it caused an intermittent problem with my fan operation. HTH.

MikeN

So you drive the car for a bit until the coolant/oil temp is up to full operating temp then stop.......do you mean with engine on or off? If no A/C is on the fans should cycle with the car running at normal operating temp while idling. If they don't something is wrong with the fan circuit independent of the A/C.....that's what I would be looking at first, basic fan op with no A/C.

Even on the hottest days the fans probably won't stay on full time if the A/C is not on, but they will (should) stay on the entire time the A/C is turned on.

The fans of my GT will run on for maybe 30 seconds or so (usually less) on only the very hottest days after the engine is shut off.......it is a rare occasion.

wds928

Mike:

I drive the car for a while, all is well, then stop, turn off the engine, go inside the grocery store, etc, return, start the car, no cooling fans, no a/c nothing. If I get stuck in traffic, the engine gets pretty warm, almost 200 F. If I get to the hiway and run constant speeds, then she cools down to normal, 180+.

Otherwise, the cooling fans have worked fine. If no A/C, the cooling fans only come on periodically, same as yours.

dr bob

Bill, the fans not running will not keep the AC from running. As you do your troubleshooting, keep this in mind.

The fan speed is determined by coolant temperature, measured by the temp --sender-- in the lower left (from rear of car: left side) front corner of the radiator, or by the freon pressure --sender-- on the top of the receiver/dryer piping on the right side, in front of the radiator and AC condenser.

The fans may also turn on at full speed when the intake overtemperature switch is closed, or when the auto trans fluid temperature switch is closed.


The hood switch connection must be open (no connection) to allow the fans to run.


A thought: Next time you experience the no-fans-run syndrome coming out of the liquor store, pop the hood and connect the two wires on that intake temp switch together. That's the switch right at the top of the intake manifold. The fans should run on high speed, may need to close the hood. If they do, your fans and primary power are OK. Controls are a separate issue, though. Read on!


After that, you need to look to see what's common to the AC button and the fan controller. The two systems are common at the "SUPPLY X" relay (true/energized whenever the starter is not engaged .and. the ignition circuit is on). From that terminal point "87" on the relay, the circuits spread through fuse 36 for the fans control power, and 37 for control power to the AC system. The relay is labelled "SUPPLY X" in the WSM schematic. The relay itself is a standard "53" relay so it's commonly available and relatively cheap. You can swap in the horn relay to this socket for testing. The "SUPPLY X" relay receives control power through the ignition switch and the "15" bus (true when ignition is on), but only engages when the starter is not engaged. If replacing the "SUPPLY X" relay doesn't do the trick, I'd look next at the wiring between the "85" terminal in that relay socket and terminal "87" of the relay socket for "STARTER V" in the main panel. If that connection is poor, the "SUPPLY X" relay won't engage, and that would cause the common AC and cooling fan failure. As Jim Bailey says: Relay Relay Relay! After that, look at wiring and connections.

You can eliminate the "SUPPLY X" relay from the possible problem list by substituting a jumper between the "30"and "87" terminals in the relay socket. This will allow both circuits to receive power whenever the key is on, regardless of the starter engagment. Use a 14 gauge jumper for this if you are going to use it for more than a diagnostic tool.

WARNING: For those reading along at home, this circuitry is different for different years of the cars. I'm doing some armchair diagnosing from the WSM circuit diagrams for the '94 car. The current flow is different from my '89, for instance, which lacks the "SUPPLY X" relay completely and has no provision to drop out the cooling fans when the starter is engaged. So don't go looking for this "solution" to a similar problem if you have a different year car with different wiring.


Bill, let me know what you find when you replace the relay or install the jumper, please.

wds928

Bob:

Thanks for the thorough explanation. As luck would have it, my most recent shipment from 928 Intl, included 3 extra 53 relays. I may play with this tonight and I'll let you know what I find. Thanks

wds928

Bob

I drove to town for gas and Barnes & Noble (sorry, no liquor store. The cooling fans worked just fine as did the A/C, even after a couple of stops. Now, perhaps it was too cool this evening, as the temp gauge never got over 185 F, near as I could tell. The needle wass just over the first, 170F line.

As to Relay X, according to the 1994 wiring diagram, it looks like Pin #30 goes through a 30 amp fuse, then to pin #2 of the fan controller I connection. I've measured this pin a couple of days ago and found it to have battery voltage of about 12.5+ volts, when at the same tome I had less than 3 volts to pins 6 and 8 on connection I with the key on and the a/c button pressed, with no A/C and no fans.

I'll drive to work with this car tomorrow and see what happens. My goal is to be able to drive to Virginia Beach tomorrow afternoon for a nice 4 day trip. I'll keep you posted

wds928

Ok, I drove to work this morning and after my second stop, the A/C did not work (button pressed, no lighted "AC", no cold air, no compressor engaged). I proceeded to work and parked the car, expecting to find the cooling fans not working either.

The cooling fans stopped as I opened the hood! I pressed the hood button down and both fans started right, but on what seemed to be a slow speed, not noisily fast as with the A/C compressor engaged. I disconnected the intake temp sensor wires and no change in the cooling fans, just running at a slow speed. The temp gauge was almost midway between 170 and 210, so I figure about 185 or so. The ambient temp was 75 F.

This is acting wierd. I'll check the voltage at pins 6 and 8 on the fan controller I connector later today.

MikeN

I agree, very strange. What about the auto tranny switch Bob spoke of? If disconnecting the intake switch wires did not stop the fans maybe this would be another place to look.

The previous owner of my GT had a problem with run-on fans, dealer fixed with a relay replacement.....but doesn't mention which one.

dr bob

Supply Relay X, terminal 30, has battery voltage all the time, a direct connection to the battery positive with no fuse. See G36 in the WSM wiring diagrams for this relay and connections. The coil on this relay closes when there is potential between the ignition circuit 15 (on when key is on) and the starter circuit (on when starter relay is engaged). See E89 in the WSM wiring diagrams for this relay and connections. So with key on and starter not engaged, this relay should close, and supply control power to the cooling fan controller through fuse 36, and to the AC controllers through fuse 37.

Supply Relay X is also shown in the lighting section at E9 in the WSM wiring diagrams. Connrections on that page show terminal 87 connected to the Fog Light IV terminal 30 (supply), so you should be able to test the funtion of that supply relay by turning on your fog lights when you are having the no-fans/no-AC condition. If the fogs don't come on, Supply Relay X has failed.

Is there a possibility that you have fan and AC function related to driving with the foglights on? A weak/burned Supply X contact may pass enough current to the controllers when the fog lights are off, not enough when the foglights are drawing additional current through the same contact.



I should be in Savannah over the weekend. Bring the car and a meter and we'll get this thing sorted. Doing some controls work at a power plant near there.

dr bob

Also--

Disconnecting the intake temp switch doesn't do anything. You need to connect the two wires together to verify the fan function.

wds928

Bob:

Just got back tonight from VA Beach. Savannah would have been a great trip, with A/C, but alas, my trip to VA Beach was in the MBZ 500E. The Porsche A/C stopped working on the way home from work Wednesday, with some low speed cooling fans and then no cooling fans. I didn't want to chance a trip without cooling fans.

Anyway, the foglights have been inoperative when the A/C, cooling fans problem has surfaced, so I will do some more testing tomorrow (Sunday) and see about replacing Relay X. Thanks for a great explanation. I'm printing it for future reference. Great work. Hope Savannah was fun. It's hotter than hell there in August. Blast that humidity, which I still can't get used to. Grew up and lived in So Cal until a move east almost 12 years ago.

dr bob

I'm still in Savannah, will be until Monday evening (assuming I get this steam temperature control problem solved...).

Glad you had a good vacation! Sounds like you are homing in on the real problem now.

In an early post, I suggested that you can jumper the Supply X relay to test. You won't want to leave that jumper in when the engine isn't running, as it will allow the lights to stay on when the key is off. I should have been more clear in the original post. Those reading along at home, make sure you add this note to that one if you need to try this.


Armchair troubleshooting from the other side of the country. Isn't this list great?