That's for the electrical load unit. When the:
-fan position is on 3 or 4 or
-the headlight switch is on or
-the rear defroster is on or
-the water thermoswitch is closed

the engine speed is raised and IIRC, the fans are supposed to turn on to help compensate for the increased electrical load. The bannana shaped section on the switch allows a ground on position 3 & 4, which engages the EL unit.

A high resistance connection for the normal 3 or 4 switch position might explain why xcelir8 had luck connecting it to the EL unit wire. The resistance on that connection may have been low enough to allow for a better ground than my original method.

Did you happen to try connecting a diode from the white wire to the green one?

 

So, does this mean the fix is not a fix?

 

Like every other electrical "fix" for this car, it seems it might work.

Try it and let us know

 

I'm going to install a relay at the ECU location that when THe AC is on the relay will provide a ground for the PFC. IN the FSM page G-22 The ECU gets a ground from the blower switch. THe relay will add additional grounding for the ECU. I beleive thats the green wire from the switch.


Alex

 

I'm confused now... buy a new switch, connect 2 diodes, connect 1 diode, add a relay at the ECU? I just want something that will provide a permanent fix... the first time.

 

There are a number of fixes that work for some and others don't

1. The diod fix is a band aid fix you have 50% of getting it to work its still relies on a ground through the switch.

2. Replacing the switch is 95% fix that is if you have no ground problems. The PFC looks for a ground through the switch. If you open up your switch you will see contacts that are worn from arcing. When this happens you start to lose ground.

3. The relay fix should be 100% because it provides the best ground path when the fans come on to the PFC. I'm installing high impedance relay parralel to the blower motor that when the contacts close the ECU get a shorter ground path.

I have some testing to do with my scope and Fluke meter to verify the right wire to short to ground.

So what ever you do your own your own if you FK up your car.

 

Well why has poss labled it as a permanent fix?

Why does my switch activate the A/C on speeds 1 & 2 but not on 3 & 4?

When you complete this, please do a DETAILED write-up on it.


Gee, thanks for the words of encouragement.

 

Well on fan setting 1 and 2 the resistance is low enough that the PFC will turn on the compressor. But fan setting 3 and 4 also activates the Electrical load circuit which creates to much resistance so the PFC doesn't see the A/C as being turned on anymore so the compressor shuts off. Hope that helps.

 

I'm almost certain that it had nothing to do with the electrical load unit coming on. If you look at the diagram, you'll notice that there is a direct path to ground for the "L/Y" wire on fan setting 1 and because of the switch's internal diode, that is also true for fan speed 2. When the fan is changed to setting 3 and 4, the ground now has to go through the resistor pack to get to ground, therefore not creating as good of a ground.

Why does most people's a/c work if they fiddle with the fan **** and get it to contact both the 3rd and 4th position? It still has to go through the resistors right??? YES, but in parallel resistances are greatly reduced. (R = 1/R1 + 1/R2+...). This supports a resistance to ground issue. I haven't measured any of the resistances so I don't know what magnitude we are talking about here.

But inserting the diodes, you eliminate the resistance on fan setting 3 and 4 while still being able to vary your fan speed. (No diodes would make the fan run full blast all the time because the current no longer has to go through the resistors)

Now as we have seen the diode fix isn't as certain as I originally thought. This is most likely due to the contacts oxidizing and adding enough resistance back into the circuit to **** off the PFC. In addition, this helps explain why a new switch can take care of the problem.

RE: installing a relay
If you put it before the thrermoswitch, it COULD cause the expansion valve to freeze up, unlikely, but possible.

HDP, do whatever method you want. They are all easy and shouldn't take you more than 2 hours tops, start to finish. I'm biased to the one that I came up with, but evidence shows that it doesn't work for everyone. Your car has similar symptoms to my car from what you've said. One thing though, if you do try my mod, to ensure that it works, you may want to take the switch apart, clean the contacts well and dab some dielectric grease on it before reassembling it.

 

Poss
When I had my switch out I could not read any internal diods in the switch. That could be why your diod trick did not work for me. I have a early 93FD the diod may have not been included in a earlier model.

Anyway I'm going to pull the switch out and install another diod. at position 1.
If that does not work I'll just install the relay at the ECU AC ground and if that does not work I'll wait for the dealer to order in a switch

BTW when I first took my switch out I cleaned the contacts with 400 grid sand paper and finished it off with electrical grease. The PFC on the Commander showed the LCD clutch working for all setting. But when the engine is running it only works on position 1 and some time 2. I'm going to pull switch again this time I'm stretching the spring contact to decrease resistance. Maybe over age and heat the springs get weak.

HDP
Don't just wait for us to do all the home work. Try the diod method. Clean your switch contacts and check for the internal diod in the switch. Let us know your results. The more we have working on this the better solutions we can come up with.

 

When the PFC "sees" the ground it turns on the indicator, and as long as there is sufficient pressure in the system, the magnetic clutch works, and the thermoswitch is closed, it *should* work. Weird.

 

OK
Here's the deal.
I installed the stock ECU with the M2 Stage 3 map upgrade just to make sure the AC does work. blows 38 degrees (Nice!)
Next installed the PFC A/C only works on SW1.
I grounded the purple wire on the ECU just like the switch does drove it and its back to 38 degrees. THis was a temp wire just to make sure it works.
Next I installed relay at switch location to ground the green wire when switch is on. The relay also gets its ground from the switch. Since the relay is not voltage sensitive a bad ground through the switch still energizes it. It needs 9 to 12 volts for the relay to work.

Now my AC works with the PFC just like the stock ECU. I beleive the real fix is to replace the switch. BTW I did order a new Switch that will be in next week for $75.00 which I will install. The relay should be the fix but I don't like to bastardize any of the electronics.

Also I beleive a grounding kit for the FD is needed. I found anywhere from 1 to 3 volts from ground to ground.

 

FYI the red wire is the ground for the switch.

 

OK, I had read that some people have had their A/C to work by putting it in between fan speeds so I went for a ride today and tried it... it worked. So does this mean I just need to clean the contacts in my switch, or should I just buy a new one?

 

Clean it and if you see pit just replace it. I just got mine it cost me $75.00
When you put it between fan speeds all it does is your putting your switch wiper in a position that is not worn or pitted.

 

I just saw this thread and no wonder my A/C wasn't getting cold when I put it in sw3 and 4. I'll try the mod when I get my car back from the shop. thanks for your informative post.

 

Let us know how it works out.



HDP,
The diode mod is cheap. If it works, you just saved something like $70. If it doesn't, you haven't lost but about $5.

 

My mechanic buypassed the ac when he installed the FC would that cause my car to stall when the ac is on?

 

It only stalls when you press the clutch all the way in and come to a complete stop

 

Maybe since your mechanic bypassed the a/c, the ecu doesn't know when to idle the car up to compensate for the a/c compressor running.

 

just to let ya'll know I don't have any problems w/my AC...Work just fine all speeds!

*cool 800 posts!

 

Well, if I have a problem I don't know about it. AC works on all fan speeds. Does A/C shut off on engine startup? how can I tell??

 

well one way would be to see put it on the screen that shows the various switches--either on or off and a few with the voltage #'s. Another is to just listen...Start the car with the AC in the on position and listen for a click followed by the engine RPM's dropping slightly.

 

My A/C works with the stock ECU just fine. When I plug in my PFC no A/C at all on any settings and the compressor does not come on. If I jump the relay the compressor works all the time, cool A/C.
I have tried a different PFC same results and my PFC turns on other cars A/C just fine.

???????????????????????????

 

Where did you buy your PFC from? What is the model number on the side( the whole thing)?