jackoncruzpr

Car in question is a 02 Civic. The light at the control turns green, A/C compressor does not engage. This is what I have tried and checked.


1. I confirmed that the relay is good. I removed the relay and applied 12V and ground to the coil ( two smaller terminals ) and it clicks off and on.

2. I removed the relay and jumpered the two large connectors to apply 12v to the compressor line and it engages. Cold air comes out of vents with car running.

3. I put relay back in the fuse / relay box and probed the coil. With the A/C on at the control there is no ground signal going to the relay coil to engage it and send the 12V to the compressor.


Also. I noticed that the engine cooling fans do not turn on. Can this be the low pressure switch? Anyone have a schematic I can look at. or guide me where to go from here?

ezone

Backprobe the wiring at the AC pressure switch......(wiring connected to switch)
Is there ground on both sides of it? Is there 5v on both sides of it?
One 5v and one ground?


Ohm check the thermal protector. Should be continuity.

Also, search this forum. I've replied to about 3000 posts covering most of the common AC problems.

jackoncruzpr

Thanks. Yeah, I looked at some threads but issues seen werent exactly like the ones I am having.

I'll have to get back with you about the pressure switch. Car is being used right now.

The thermal protector is OK since I can manually get the compressor to turn on by jumping the pins at the relay.

So when the A/C button is engaged at the Heater / A/C Control Panel it sends a ground to the low pressure switch which in turn talks to the MPU?

Would this also explain why the fans dont turn on as well?

ezone

Incorrect assumption. See a wiring diagram for the system on 02-05 cars.
Yes, and moreDepends.

The PCM controls the clutch relay and the radiator fans. If the PCM never sees an AC request it won't turn the clutch nor fans on. There are several possible reasons the PCM may not see that request.

jackoncruzpr

You are right. I was looking at a diagram for a 01.

So I disconnect the 3 pin connector and check for continuity on the 2 pins that do not lead into the compressor coil that should tell me if its the thermal protector or not.


So in my case I think 3 situations can play out.

1. I genuinely am low on pressure

2. Bad low pressure switch

3. Bad thermal protector


I'll update later with my findings

tmarron0

Just curious but did you check for freon? I thought the clutch wont engage if it has no charge on it. I may be wrong though

ezone

Right.
2 outer pins are for the thermal protector.
Center pin is for the clutch field coil.
But you said it got cold.
If pressure was low, the pressure switch would be open.
Test it.
See aboveTest, see above




Remember the part where I mentioned checking for 5v or ground? This is quite important info for the diagnosis.

(I'm all about accurate diag, that's where I make my money.)



Got any other weird electrical issues happening in the car?



He said it got cold when jumped, so I assumed it has enough freon to at least operate if it can do that.

jackoncruzpr

well I finally got access to the car. first thing I did was to test the thermal protector and found to be no continuity there.

Ordering one..........will put on and update from there

Tman

I'm having a similar issue I'm having trouble finding the thermal protector. Where is it located?

ezone

On the compressor.

Tman

Ok thanks I'll check it tomorrow.

jackoncruzpr

New Thermal protector fixed my issue. I replaced it without having to remove the PS pump or alternator but it was a bitch. You have to get to it from the side and underneath the front clip. Limited space between the subframe.


You can test the termal protector without having to get to the connector attached to the side of the radiator shroud.

There is a set of wires running inside and underneath the core support. Follow the thermal protector connector up on top.

Remove the clips to give you more access and peel back the tape. You want to check for continuity between the two smaller wires of the 3 in that bundle. I used some safety pin needles to pierce through the the center of the plastic sheath and then used my cheapo harbor freight DMM to check for continuity.

jackoncruzpr

You can test the thermal protector without having to get to the connector attached to the side of the radiator shroud.

There is a set of wires running inside and underneath the core support. Follow the thermal protector connector up on top.

Remove the clips to give you more access and peel back the tape. You want to check for continuity between the two smaller wires of the 3 in that bundle. I used some safety pin needles to pierce through the the center of the plastic sheath and then used my cheapo harbor freight DMM to check for continuity.