Little Background...

1995 1.5L Civic DX 4-dr, purchased in November. Finally gotten around to repair the A/C Compressor this past weekend (money issues). The "original?" A/C Compressor housing was cracked and and I could literally see in.

Anyhow we removed the old one and plopped in a refurbished one (yes I put a new dryer in as well). We flushed it with the flushing liquid (and a stupid $69 bottle and hose to flush it out with! grrr.), and did what the Chilton manual said to do. Turn the A/C on Max Cool and A/C on and start the car and we began to fill the system.

Here is my dilemma.

1) now the that coolant is charged (high side reading 225 psi, low side about 40 psi) and system cooling nicely, I go to shut off the A/C from the dashboard control - the compressor clutch is still engaged!
2) pressure builds to over 400 psi (yikes)! I have to quickly shut the car off, or turn the A/C Blower back on to get the condenser fan to turn on and lower the pressure.
...
<sigh>
...
3) I turn the car off, and start it up again -- the clutch is disengaged for a second while the car goes to idle speed, then it engages. I took the two relays (condenser fan relay and compressor clutch relay) apart so I could view them in action. The relays come on (and off) when the compressor comes on and off.
4) the compressor relay seems to be controlled by the ECM A15(?) line, which makes sense in the start up of the A/C after the engine has come on.
5) the compressor will "compress" even if the following conditions exist
- low pressure switch open (system empty) or closed (system charged with new 134a)
- A/C button is off at engine start
- Blower is off at engine start
- A/C button is turned off while engine running
- Blower if turned off while engine running

The thermal overload seems to be ok.
The little diode "seems" to be ok - I haven't fully verified, but I believe that is more crucial for the condenser fan
The compressor will stop if I disconnect the red wire connector to it.
The red wire reads 0v while engine is started, 12v 1 or 2 sec after engine starts

The only way I could prevent the compressor from running is to remove the 20A fuse in the U/H F/B for the Condenser fan/Compressor clutch.

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I wonder if this is how the first compressor housing was cracked and disintegrated when I bought the car - the compressor started to run and build up pressure without the condenser fan and built up pressure to past breakage...

Do I have a bad ECM module? Is there a bad sensor? What do I check to get it to cycle properly (which it won't) and shut off when I turn the dashboard A/C controls off?

Desperately seeking advice.

Thanks in advance!

~lum

 

sounds like the refurbished compressor - return it for a different one
has the car ever been crashed?

 

Hmmm.

I know that I can put a toggle switch in between the compressor and the rest of circuitry and turn the compressor on and off manually (I had it rigged up that way for a couple of hours). I believe the clutch works fine. I can see the relay energize (and stay energized) 1 second after the car starts - that signal is provided by the ECM, I believe.

What is perplexing is that the ECM doesn't seem to respond to the "A/C Pressure Switch" signals. If I disconnect that line, the compressor should stop or not run, right?

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The car may have been crashed - I don't know. I bought this as a "hooptie" for my daughter, and so far it's working out (except for the hot weather).

I think I have ECM problems, but don't really know how it's supposed to work, entirely.

 

it sounds like a short somewhere, if you have a voltmeter check the positive terminal on the battery and the positive connector on the pump - if you read more than 0.5v you have a short; readings for negative side should be below 0.25v - i'll have a look at my one tomorrow with a voltmeter (left it in work) and see if i can help any further

is the ac blowing out cold air in the car?

 

Thanks!

Yes, it's blowing cold air, btw. I just can't shut it off!

 

can you check it with the voltmeter like i mentioned?

how much r134a did you put in?

 

Working on Ohming it out -- I only get to see the car in the early mornings before I go to work. My daughter has it until 10 p.m. when she comes home from her work.

Gonna check it out this morning. You're right - I may have a shorted dashboard switch (or elsewhere).

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I've put about 19 oz bottle of 134a in there. Of the 19, there was 3 oz PAG oil. The compressor (I'm told) has a nominal amount of oil in it as well. Probably needs a little more charge because I don't think I've emptied the bottle completely.

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A separate question - what is supposed to make the Compressor cycle on and off? (or does it)?

Thanks so much for your help.

~lum

 

<sigh> [X(] It might not be until tomorrow night when I get to see the car again. My daughter has decided to stay over at her friend's house last night, and I've not had the chance to read the voltages.

But it does sound more and more like the dashboard A/C switch is shorted on one side. When I press the button, the green light comes on (and goes off). I just never thought to read the voltages on the other side of the switch.

Boy I sure do wish she'll get back here with that car... [&:]

~lum

 

i'm pretty sure the pressure sensor activates the relay to turn it on and off

 

Hi! I just ohmed it -- kinda confused.

From the positive terminal to the positve wire on the A/C Compressor (like your message describes)

-- Car off --> OPEN
-- Car on, A/C off --> 0.02v
-- Car on, A/C on --> 0.02v

Additionally, I removed the Compressor Relay and the readings are:

-- Car off --> OPEN
-- Car on, A/C off --> OPEN
-- Car on, A/C on --> OPEN

From the negative terminal to the ground side of the A/C compressor

-- 0.00v

I finally got a hold of some schematics from here (http://www.hondahookup.com/manuals/) for the 95 Civic DX (easier to understand than the Haynes manual). Page 22-6 says the 12v that supplies the positive side of the Compressor and Condenser Fan relays come from a fuse and the ignition switch. So there's always going to be 12v sitting on the relay as long as the car ignition is switched on.

The problem is that the ECM sinks the negative side, turning the relay on (in turn engergizing the compressor clutch). There's nothing turning off that side. There is an A/C pressure switch that supposedly serves as the safeguard or control. He doesn't do anything.

The ECM keeps the compressor relay circuit open on engine start (thank goodness). Then it'll make the circuit once the engine is idling - so I know that the delay circuit is working.

Now I'm wondering if the signal from the pressure switch isn't getting back to the ECM, or it's the ECM itself that's bad...

~lum