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A/C clutch won't engage


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kgrone
Novice

Jan 1, 2018, 1:12 PM

Post #1 of 9 (384 views)
A/C clutch won't engage Sign In

Howdy all,

2004 honda accord, 3.0L, 160k miles

Starting in August, my AC clutch began disengaging after a few miles of driving (assumed it was due to the coil heating up)and then it eventually quit working altogether. I finally got around to digging into it this past week and determined the clutch was bad. I replaced the compressor/clutch assembly and it seems to be in working order now, but the clutch still won't engage through the clutch relay in the underhood fuse box. Here is where it gets weird for me. With the engine running and AC turned on:

1. I have 13V across the two relay coil terminals (seems to be getting a call for AC to the relay in order to close the relay)
2. I have 13V across the two load terminals (voltage and ground through the clutch seem good)
3. If I jump the two relay load terminals the clutch engages (clutch seems to operate correctly when voltage is applied)
4. If I swap the clutch and fan relays, the fan works with both, but the clutch works with neither (seems the relays are good)

My only thought is I'm somehow not getting good contact between the relay and the terminal but I have messed with that quite a bit to no avail. Anything else you guys can think of? I am a plumber rather than a mechanic, so it's very possible I am missing something.

Thanks,


Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

Jan 1, 2018, 1:32 PM

Post #2 of 9 (381 views)
Re: A/C clutch won't engage Sign In

If you have 13 volts on both sides of the relay coil, that means the relay isn't being grounded by the Ecu for some reason. Does the cooling fan run and engine speed change when you turn on the AC? Does the blower work? What are your refrigerant static pressures?





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Jan 1, 2018, 1:33 PM)


kgrone
Novice

Jan 1, 2018, 1:40 PM

Post #3 of 9 (375 views)
Re: A/C clutch won't engage Sign In

Thanks for the reply!

13V is across the relay coil, not on both sides (13V on one side and ground on the other). The cooling fan does run and the blower does work.

Static pressure is at 38-40psi (set based on R134 engineering tables as it was 35F outside when I worked on it earlier and also measured refrigerant when charging). If low pressure was the issue I don't believe I would be seeing voltage across the relay coil, as the pressure switch should cut it off, correct?


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Jan 1, 2018, 1:57 PM

Post #4 of 9 (356 views)
Re: A/C clutch won't engage Sign In

160K if nothing done yet check clutch air gap. If much over .020 can be intermittent and over .030 will not engage you adjust it to be closer if so but not yet. Coil if seriously too hot and melted is unseen behind clutch. Test just the two terminals with a DVOM for about 4.5 OHMs. If failed would be infinity or nothing.
You can check clutch air gap roughly with a standard thickness biz card folded shouldn't be able to slide one in the gap,


T



kgrone
Novice

Jan 1, 2018, 2:02 PM

Post #5 of 9 (352 views)
Re: A/C clutch won't engage Sign In

Thanks for the reply, Tom!

I just replaced the entire clutch/compressor assembly with OEM (Denso). The clutch also engages when I jump the load terminals at the clutch relay, so I am fairly certain the air gap is within tolerance.

I am not an electrician or mechanic, but somehow it seems that I am getting no current through a closed relay, but the relay is not bad.


Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

Jan 1, 2018, 3:04 PM

Post #6 of 9 (338 views)
Re: A/C clutch won't engage Sign In

You jumped the load sides of the relay contacts and got the compressor clutch to engage. That means you have power and ground on the clutch circuit. As for the Relay coil you stated you have battery voltage on one side and 0 volts on the other side. That indicates that the relay is being energized by the ECU. You swap the relays and the AC relay works for the fan. There has to be something wrong in your testing unless you have a pin fitment issue in the relay cavity or else the system should be working. Double check your relay coil supply and ground voltages again. Make sure you volt meter is grounded at the battery negative terminal. Those AC clutch micro relays had a lot of issues so keep that in mind





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Jan 1, 2018, 3:08 PM)


kgrone
Novice

Jan 1, 2018, 3:12 PM

Post #7 of 9 (330 views)
Re: A/C clutch won't engage Sign In

Agreed on all accounts. Thanks for your time.

I will check it once again and let you know if I find anything new. Just wanted a sanity check to see if I am overlooking anything or working on bad assumptions.


kgrone
Novice

Jan 7, 2018, 1:18 PM

Post #8 of 9 (290 views)
Re: A/C clutch won't engage Sign In

 

There is voltage to the relay coil, however, a continuity test from the opposite relay coil terminal to ground failed, so it appears I am having a grounding issue. Based on my research, it looks like that is a pressure switch issue or an ECM/PCM issue. The pressure switch has 4 pins and I have not been able to determine what each pin does. The only help I have found online for testing pressure switches is for 2 or 3 pin switches.

Any help on how to test the pressure switch?

Thanks in advance!


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jan 7, 2018, 5:58 PM

Post #9 of 9 (276 views)
Re: A/C clutch won't engage Sign In

The ground control for the relay is controlled by the PCM. The PCM will not turn the relay on until it received an "on" request from the switch and is totally satisfied with all the inputs it monitors in the system to include both pressure sensor circuits and the engine coolant temp sensor.








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