A/C Problems

[gadget73]

I'd find out why its not working first. If the relay is being energized to drop out the compressor, the ECM probably thinks you have your foot to the floor. Elsewise it may just be a bad relay. You shouldn't need to bypass that in order to have the AC work correctly. Besides, the compressor isn't going to be thrilled about spinning at high RPM anyway. Having it drop out under heavy throttle is a good thing.

[sly]

The bypass would just be a "check the relay" thing. If it works bypassed... then check if the coil is being energized (one coil pin should read 12V, the other will be short to GND if switched and high resistance if not switched). If the ECM is switching the WOT relay... might just be a bad TPS.

[BigT]

Got it!

[BigT]

Question?

I went to see if the relay was bad by using a jumper wire. Something strange happened (IMO) before I used a jumper. I disconnected the relay I wanted to test and left the other one connected. I turned the car on (RUN) position and the A/C clutch engaged. Now I'm worried if I use a jumper wire I may cause an arc or short something out.

Is this normal?
Is the possible bad relay stuck in the cut-off position?
My guess is both relays are required for the WOT cut-off system to work. Am I right?

[gadget73]

Its only got one relay for the cut-out. With the relay removed, you should not have any power to the compressor clutch. It uses the normally closed contacts to pass voltage through from the switch to the clutch. The relay is powered in order to shut off the ac compressor.

If you pulled a relay and the clutch still worked, you probably removed the ECM relay. There are 3 up there, one is for the fuel pump, one is for the ECM, the other is for the AC. Remove the ECM relay and the AC relay will not cut out, and the fuel pump will not operate.

Just a mention too, the AC coil typically will not have any power unless the engine is running. The ECM drops the compressor out by engaging the WOT relay while cranking to allow for easier startup. The ECM has no power in "acc" mode, so it won't drop the compressor out.

[86VickyLX]

Its fairly basic. Power comes in to the climate control switch, out to the WOT cutout relay on the driver's side fender, through that to the low pressure switch, from there to the compressor coil. If you don't have voltage at the low pressure switch, check at the WOT relay. If nothing there, its somewhere back at the head unit. If you have power through to theh coil on the compressor, the clutch coil is bad.

I think that's incorrect. The pressure switch gets power first from the a/c head. Then it goes to the WOT relay, then it goes to thee clutch on the compressor. I just fixed Andrew's a/c on his 89. To test I ran a wire from the output wire on the pressure switch, and directly to the clutch. Turns out the plug on the WOT relay was messed up. Moving the wires around in there made the compressor clutch engage and disengage rapidly (as if there was a bad connection) Rewiring the system with a standard relay with nice clean contacts fixed the problem.

Also in my endeavors in the past my car used to go through computers like it was nobody's business. After replacing my wire harness, it all stopped. Though, something was bad in the last computer I had in there, as the A/C would never come on when the car was running. The computer saw fit to keep the WOT relay energized whenever the car was on.

[BigT]

MegaSquirt ECM

My apologizes if this has been confusing. I finally figured it out.

Short Story:
The ECM is cutting out power to the A/C clutch or better yet, activating the WOT relay.

Long Story:
First, I was messing around with both the ECM and the A/C WOT relays and didn’t know which was which. I was getting confused as to why one of the relays being unplug would engage the A/C compressor. Once I figured out which relay did what, it came together for me. The WOT relay would cut power to the A/C clutch every time the ECM relay was plugged in and the engine in RUN. Here are the wires involved:

WOT Connector Wires	WOT/ECM Plugged In	WOT Unplugged/ECM Plugged In	WOT Plugged In/ECM Unplugged
Pink/Blue Stipe (Power - Climate Control)	AUX = ON	AUX = ON	AUX = ON
	RUN = ON	RUN = ON	RUN = ON
Red (Activates WOT)	AUX = OFF	AUX = OFF	AUX = OFF
	RUN = ON	RUN = ON	RUN = OFF
Black/Green Stripe (Feeds the A/C Clutch)	AUX = ON	AUX = OFF	AUX = ON
	RUN = OFF	RUN = OFF	RUN = ON

The ECM is supplying power to the Red wire and activating the WOT Relay and cutting power to the A/C clutch. I unplugged the WOT relay and used a jumper wire between the Pink/Blue Stipe wire and Black/Green Stripe wire, and the A/C clutch engages while the engine is running. Nice and cold!

I haven’t used the A/C since I installed the MegaSquirt ECM. I’m sure there is a configuration setting I need to change to get it to work properly. I have barely scratched the surface of all the settings this ECM has and can do. I just have to fine it and set it. Thanks again for everyone’s help!

[86VickyLX]

The orange wire is actually the ground from the computer. That turns on the relay. The red wire is energized anytime the ignition is in the run position as it's the main power feed to every 12v source in the eec-iv system (except for the o2 heaters)

[gadget73]

hm, non-stock ECM. That one I do not know the answer for.

[BigT]

It’s the ECM. I contacted a tech at MegaSquirt. After some back and forth e-mails, they were able to tell me which wire to cut at the harness to deactivate the WOT Relay. That means the A/C will not cut off during WOT.

I’m going to go the other way and use a jumper wire. A guy at work is heavy into aftermarket fuel injection systems, though all his stuff are Mitsubishi cars. He thinks there might be a way set parameters like TPS above a % and engine load above a % to create a port to send 12 volts to a wire. Then I can use that wire to trigger the WOT relay.

[gadget73]

Possible the configuration is opposite on the MS. THe Ford system applies no voltage to make the AC run, but energizes the relay to shut it off. WHat you could do is wire a test light off the relay and see if the light goes off at full throttle. If it does, you can simply re-pin the relay socket so it works with that sort of signal. Its a case of moving one wire in the relay socket.

[sly]

You could also set a switch on the throttle itself to trip at 3/4 WOT to ground the wire from the WOT coil to ECM (run to the switch then ground). Problem solved.

[BigT]

Possible the configuration is opposite on the MS. THe Ford system applies no voltage to make the AC run, but energizes the relay to shut it off. WHat you could do is wire a test light off the relay and see if the light goes off at full throttle. If it does, you can simply re-pin the relay socket so it works with that sort of signal. Its a case of moving one wire in the relay socket.

You could also set a switch on the throttle itself to trip at 3/4 WOT to ground the wire from the WOT coil to ECM (run to the switch then ground). Problem solved.

Both good ideas. Thanks! I always get good advice from this forum.