AC Fix?

Worked on the AC today. It blows cold but I had to rewire some of it.
The relay to run the compressor does not get 12 volts. I jumpered the green with yellow tracer coming out of the "Auto Compressor Control Unit" behind the glovebox to the 12v from the AC switch. Works great. The signal goes through the two way pressure switch on the dryer and the temperature switch on the thermostat housing. Since the pressure switch lets the compressor run I know I have a full charge.
Any ideas on why the "Auto Compressor Control Unit" will not supply the 12 volt signal?
Also the signal seems to depend on the "MFI Control Unit" What is the "MFI Control Unit" and where can I find it?

Car had the KeyDiver chip if it matters.

 

I think the MFI control unit is the ECU, one of the pins from the ECU harness must be grounded for the compressor to engage.

 

Quoting 1439of2000:
Car had the KeyDiver chip if it matters.



Yeh, right. /ubbthreads/images/graemlins/dunno.gif
Anyway, yes, the ECU *does* control the AC compressor, BUT it also must receive input from 2 other sensors and the AC switch first. 12 volts leaves the AC switch on the dash, goes through the HI/LO pressure switch on the accumulator, then thru the coolant switch sticking straight up out of the thermostat housing. That switch, or more importantly the wiring to it, is usually the culprit, not the chip.
After it leaves the coolant switch it goes to the ECU. If everything else is OK as far as the ECU is concerned, it grounds the output terminal to activate the AC clutch. The TMO software is a good way to troubleshoot it, as it shows both the input and output signals to the ECU.

 

Jeff,
No disrespect intended. I simply did not know if your chip added another layer to the AC unit (such as turning off AC at a certain boost level). I apologize if I sounded rude.
The Pressure switch and the temp switch on the thermo housing (and all the wires) seem to be working since my temporary fix is routed through all of them. Where do you get the TMO software?
The ground side of the AC compressor relay seems to be fine. The 12v side seems to be the problem. 12v from the AC switch goes into the "Compressor Control Unit" (behind the glovebox). The 12v does not come out of the "Compressor Control Unit" (the green with yellow stripe, number 6 on the factory wiring harness).

 

Quote:
The Pressure switch and the temp switch on the thermo housing (and all the wires) seem to be working since my temporary fix is routed through all of them.



I don't think so. If I understand what you have done, you have bypassed it right at the AC clutch relay, which is the very END of the line. You need to start back at the beginning. As I said, the +12 volts from the AC switch in the dash MUST end up getting to pin #7 of the ECU:
click
Then, the ECU grounds pin #65 to activate the relay you bypassed. I think you will find that you don't have 12 volts on pin #7. /ubbthreads/images/graemlins/wink.gif

Quote:
Where do you get the TMO software?



Its a little difficult to use, since its an older DOS/Win 3.0 application, but if you have an old notebook laying around with a serial port, its a very nice logging program:
click

 

Thank you Jeff. I'll look again.
I gave my serial port laptop to Jay with the Porsche. I may have another laying around.
I understand you like to dive in the keys. Have you ever thought about Guam? I learned to dive there. 84 degree with 300 visibility on a bad day. Unlimited visibility on a good day. I think it was around 85 species of coral. GREAT diving.

Thanks again,
Glenn

 

I'd LOVE to get to the South Pacific. My eye has actually been on Palau, but I'm not that picky. /ubbthreads/images/graemlins/wink.gif

 

After learning to dive in Guam I had the chance to dive in Hawaii. I turned it down since the water was too cold and the visibility was bad. Also the cost was out of this world. Kind of wish now I had tried. I have snorkeled in Hawaii.
Right now I simply live too far from any water to dive. I am jealous.
You may check out Chuuk. formerly known as Truk. You have to have a local guide, you cannot dive on your own but it is supposed to be fantastic. Lots of WWII wrecks.
I got to dive on the only knows WWII wreck resting on top of a WWI wreck in Apra Harbor, Guam. The Cormoran (German) and the Tokai Maru (Japanese) sunk in exactly the same place. Depth was oer 100 so bottom time was limited. Still it was a great dive.

 

[gtluke]

that computer auto control thingy behind the glovebox died on my galant about 4 years ago, i suspect yours died also. grab one from a junkyard, its not gvr4 specific or anything but it is galant specific.

 

I'm afraid you might be right. Anyone have one laying around for sale?

 

click

Did a little more diagnosis. 12v from the AC switch goes to pin #2 in the Auto Comp Controller. From there it leaves via pin #6 (Auto Comp Controller) for pin #7 of the ECU. On it's way it passes through the dual pressure switch and the coolant temp switch. There is no 12 volt at pin #6 Auto Comp Controller so...it does not send 12 volt to pin #7 in the ECU.
I removed pin #6 from the Auto Comp Controller and jumpered it to pin #2 (the 12 volt signal from the AC switch). Now it sends a 12 volt signal to pin #7 in the ECU and I get cold air. It is now just an on/off contol, no thermostat. But cold air in West Texas is wonderful.
And yes, the fan in front of the AC condensor turns on. It is very quiet compared to the monster fan I had in the Porsche.
I think I need a new Auto Comp Control Unit. The numbers on unit are
MB276780
CAA531C001
SG-17

Anyone have one they would be willing to sell? There are not too many junk yards in the area and EBay had nothing. It is located under/behind the glove compartment.

Thank you everyone for the help!

 

[ktmrider]

Nice troubleshooting! There are quite a few part outs in the FS section, no doubt one of them can hook you up.

 

Holy thread resurection Batman!

Finally got moved and settled in enough to install the AC comp controller that Toybreaker sent me. AC works perfect now.
Thanks everyone!