Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[PhilStubbs]

ok, finally had some time to get serious with the troubleshooting. its looking like the ecu is the culprit but it would be nice to have some input before i buy another one. the a/c wiring diagram is below.\

dash switch is confirmed good
pressure switch is confirmed good
all fuses and relays confirmed good
compressor and clutch confirmed good

the reason i am pointing towards the ecu is, turn the key to the on position. if the a/c button is pushed the blower fan and condenser fan comes on along with 12v+ applied to the compressor relay. after a few seconds the fans go off. turn the a/c switch off and none of that happens. once the engine starts the compressor relay no longer gets 12v+ from the ecu. another key to my decision is the ecu has gotten pretty wet for a year or so from a water leak. thoughts?

[ratcityrex]

I would put a vom on the output of the Ecu, key on the car and check to see if the power goes away after a couple of seconds.

[PhilStubbs]

i put my powerprobe on the ecu output. 12v+ key on, nothing engine running

[PhilStubbs]

SKEET SKEET!!! found an ecu locally to test with

[ratcityrex]

Sweet deal.

[PhilStubbs]

Turned out to be a 97 ecu and I need 99 up

[HiProfile]

If the fans turn on then off, the ECU is trying to activate it, but senses something and turns if off. Check A17 for the comp clutch relay, see if the ECU sends power for the period the fans are on. You could feed A17 power for a short while (however ballsy you are) to see if the system comes to life. That would turn on the compressor clutch, basically overriding everything. FYI holding it on too long if there's another issue could blow shit up.

You'd also want to check the status of A27 for the input signal that tells the ECU to turn on the compressor clutch & fans. Fake the signal and see what works. If that's the issue, it could be a bunch of things in the heater control panel (no idea what it looks at to output the AC signal), but most likely the evaporator sensor. If the sensor says the evaporator is iced up, the AC obviously wouldn't turn on.

[PhilStubbs]

The climate control panel has a self diagnosing function. It claims the evaporator temp sensor is good.

The ecu send out 2 signals when the a/c is on. One to the fans and another for the compressor clutch. I did activate the clutch manually through the relay and it works. The ecu puts out a 12v signal with the engine not running but as soon as the engine starts that signal goes away.

I opened the ecu also, no sign of water in it at all. So if it is the ecu, something went bad on its own.

[fearsomedan]

I think you guys are seeing this wrong.  At A17, the pcm sends a ground signal to the clutch relay to activate it. At A27, it grounds the condenser fan relay to activate that. Use the power probe to see if your getting ground at those points when ac is turned on. If not, check to see if your getting the signal from the high pressure switch to the pcm.

[PhilStubbs]

I get 12v+ at times and basically nothing others. 5v+ goes into and comes out of the pressure switch. That signal dies get all the way to the ecu also.

That thought crossed my mind that the ecu would provide ground for switching, but I kept getting 12v+ so just figured it was different than I expected. :/

[HiProfile]

I'd almost suggest looking at the thermo dodad on the compressor itself, I've had one that was bad. All 90's Honda compressors use the same thing, it's part of the wire that leads to the clutch. I doubt it since the fans turn off w/o any feedback from the clutch, however it could be looking for pressure instead. No pressure after a few seconds could be enough for the ecu to turn them off.

[PhilStubbs]

The ecu never clicks the compressor relay at any point. I'm not trying to steer this to the ecu cause I want it to be bad or anything. I'm just stating my findings as they pertain to everyone's suggestions. Honestly, I'd prefer a broken wire or something free.

It is really awesome that the helms manual completely ignores the fact that part exists though.

[fearsomedan]

I get 12v+ at times and basically nothing others. 5v+ goes into and comes out of the pressure switch. That signal dies get all the way to the ecu also.

That thought crossed my mind that the ecu would provide ground for switching, but I kept getting 12v+ so just figured it was different than I expected. :/

You would see 12 volts at the wires to the relays from the pcm because its not being grounded. I would try to get the wiring diagram for the pcm to see where the grounds points are. If the pcm ground points and wiring are good, I think the pcm is the culprit.  It is not grounding the circuit.

[PhilStubbs]

As far as I know, it only grounds at the typical Honda spot on the thermostat housing. If it wasn't a good ground then the car wouldn't run. I'll check the helms manual for sure. I'd much rather clean a ground than buy an ecu.

[92CXyD]

Ground for the a/c clutch is at the ground junction  beside the back of the passenger headlight. 

Looks like a white or clearish box with at least 4 wires bolts to the fender.   

[PhilStubbs]

The clutch ground is good. If I manually kick the relay the compressor works.

[PhilStubbs]

Tried 2 different ecus. Still no a/c.

[PhilStubbs]

Turned out to be the ground source the ecu uses to provide ground to the clutch relay. Ran my own ground wire to pin A27 and everything works exactly as it should.

[PhilStubbs]

The plot thickens a little. It seems my ground was somehow a bandaid fix. Today I changed the blower resistor cause the blower only worked on high. I'm not sure why, but I decided to pull my ground wire after changing the resistor. A/c works fine. I guess it needs feedback from the blower resistor. There is no mention of this at all in the helms manual.