So i have read nearly all the AC issue threads and learned alot. Here is my situation which is similiar to alot but need a little more direction and guidance.
First off AC quit working. Inside blower works and controls show green.
Rad fan/Cond Fan/Compressor do not engage when switch is turned on.
Relays all good (swapped back and forth)
Jumper 12v across pin 1 and 2 of Compressor clutch relay and clutch engages
Jumper 12v across......Rad fan relay and Condenser fan relay and fans begin to run.
Thermal protector measures 3.1 ohms across pin 1 and 3 of the connector.

ECM troubleshooting
I was able to sound out ECM pin E14 to the Compressor Relay pin 4.
Jumpered a ground to ECM E14 and compressor clutch engages
Sounded out ECM B2 to Rad fan/Compressor fan relay pin 4
Jumpered a ground to ECM B2 and both fans begin working.

I have read about Multiplex Control Unit. What is this and where is it. Am I heading in the right direction or did I miss something important.

Schematics that I have found online for this civic are not of the best quality for detailed items but got me in the right areas. https://estore.honda.com/service-exp...scriptions.asp might be a resourse if someone has used it and can give me their opinion. Its $10/day and i assume you can find good quality schematics.

Any Help and advice will be greatly appreciated.
Jeff

EDIT: I can't read LOL

Including the 15,000 or so AC related threads that I've posted in?
Don't believe a word of it...... I park in handicapped spaces because I can't even read.




Start the engine and turn on the AC at the control panel.

Go to the 2 wire plug for the pressure switch on the receiver-drier and check the blue wire, it should be grounded when the AC is turned on.

Thanks for the reply. I will check that pressure switch in the AM.

Ok, with AC turned on the blue wire on the receiver/dryer goes to ground. I assume that means the receiver/dryer is good.

No. That blue wire comes from the control panel and only tells me it's doing what it's supposed to do.

The AC request path is this:
Control panel > pressure switch > thermal protector > MICU > PCM

The ground 'signal' should make it all the way to the MICU where it turns into data before it goes to the PCM, instead of a simple ground. So the pressure switch must have continuity and the thermal protector must have continuity.
You could jumper each of those just to see if the system will kick on the radiator fans (the compressor can't run if it's 3 wire connector is unplugged, of course)

If the pressure switch is open....it's probably lost the freon.

Does the key beeper work? Do the courtesy lights work right? Odd electrical gremlins? Intermittent wipers work right? Keyless entry?

No weird electrical gremlins. So where is the MCU located? Or is it within the ECM. I currently have the ECM pulled from behind the glove box and open. So correct me if I'm wrong. We just checked the pressure switch correct? I think I have a set of old pressure gauges form the old freon days. I could at least check the pressure.

Does the pressure switch have continuity, or not?

If your gauge set is for R-12 it won't hook up to R-134 fittings.

Yes the pressure switch went to ground when I turned on the AC therefore continuity.

If you had the switch harness unplugged, you didn't check the switch.



If you only checked the blue wire for ground, you cannot conclude nor infer anything else is ok.

So i guess i could do that with the plugs connected and slip a needle point probe/paper clip into wire entrance of the plug..

so with the plug back on the dryer and ac on the voltage drop between the two pin is 12v. Resistance is 21ohms

Ummm.....ok....Unplug the 3 wire connector for the compressor (probably clipped to the fan shroud), the car harness has wire colors

blue/white
blue/red
red

With the engine running, use a jumper wire to connect a ground from battery negative to the blue/white wire-- and see if the radiator fans kick on




Did you find a gauge to get a pressure reading?

Well I feel like an idiot. Sometimes the obvious problems is in the shadows while your brain thinks catastrophe and looks for the harder more difficult problem. I decided to push the needle valve on the high/low pressure side. NOTHING. Absolutely no coolant in the system. No wonder. I really appreciate all your direction. I have learned alot about this 'ground' based system, PCM, MCU, relays...etc. Now to track down and see where my coolant leaked from.

The pressure switch ohm test SHOULD have read as "open" circuit or infinite resistance.

IRL I check some other things before bothering to check freon level, just because 3/4 of the problems I deal with are NOT low freon LOL

Ok then. I will continue to check the circuitry. The resistance between the two wires of the pressure switch was not "open".

Stop. The system quit working because it has no freon.

The pressure switch should have read as open though, don't worry about it right now. Reconnect plugs.

Refill freon first and find where it leaked out at.

After there is sufficient pressure in the system (about 40 PSI or higher) the compressor should turn on normally .....until the freon is lost again.

Yes, I was planning on refilling it and then re-assessing the situation.