Strange AC behaviour

[Warpc0il]

What can cause the AC compressor drive clutch to switch on/off constantly at idle, even when AC mode isn't selected on the HVAC control?
I've pulled the relay to stop it driving me mad.

 

[lfhoward]

If the HVAC controls are set to defrost, the AC will run. And if it is low on refrigerant, it will short cycle.

 

[KJowner]

Hi WarpcOil, bit more life here than the UK forum.

 

[tommudd]

Not a good idea to pull the relay, it is supposed to be that way

 

[Warpc0il]

I understand it should do this in some modes of the climate control, but it does it in all modes, all the time, regardless of how I set the controls.

Hence the confusion.

Strangely, it only started doing this the same week that the wipers stopped "parking" in the down position. I've had a problem on other cars where the contact track on the wiper motor has dirt (or a burnt section) so the wipers can choose to stop there, but the Jeep's wipers stop in random places - doesn't even complete the cycle if you pull for a wash/wipe.
Also getting random 02 heater circuit DTC's, never one at a time, always both rear sensors at the same time, which clears fine and then comes back a few days later.

Now starting to wonder if there's a gremlin in the electrics, like a common earth has gone bad, that all these systems share.

 

[tommudd]

Well now, with more information it could also be a bad battery , computer going bad etc

 

[Warpc0il]

Hi WarpcOil, bit more life here than the UK forum.

Yea, I sometimes wonder if I'm the only one still stupid/stubborn enough to still drive a 3.7 KJ in the UK....

 

[blackhawk]

Well, the two libbies I have, do the same that yours... Both switch on/off constantly at idle regardless the position of hvac. It's a normal circle as far as I know

 

[LibertyTC]

What year of jeep ? I suppose after 2005 the climate control changed?
My 2004 has 3 positions where the A/C wont run, thankfully.

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Can you post a photo of your control?

 

[Warpc0il]

Mines a 2002 so the same controls.
However, mine cycles in all positions.
There's definitely something strange with electrics as my ODB2 logger shows the voltage swinging rapidly between 11.5V and 13V with engine running. Not only is this varying much more than I'd expect but it's about 1.1V down on a direct measurement across the battery.
There're a couple of earthing points on the inner wing under/behind the battery tray that are really crusty.
She's got an MOT retest on Sunday, after I had to replace both rear suspension arms, so I'll wait to see how that goes before I get stuck into the electrics.

 

[LibertyTC]

Use a volt ohm meter to compare voltage at battery terminals while running.
How old is battery? Wire brush both terminals, ensure no corrosion anywhere, and tight.
Alternator issue?
My Jeep with AGM Odyssey battery reads 14.5 Volts while running on start up in winter.

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[Warpc0il]

The battery is nearly new, fully charged, with clean and tight connections.
The voltage readings there are as expected.
However, it's the "voltage" parameter reading on the ODBII output that's, significantly lower and much less stable.

This suggests that either;
- there's a poor power connection to the PDM/ECU, or just the ODBII socket
- there's a poor earth connection that affects the ECU and/or ODBII socket.

My guess is the latter, given the strange behavior of the wipers and the a/c compressor drive, as the wipers definitely aren't linked to the ECU, and I'm not sure about the compressor clutch (on some cars it's ECU controlled while some it's just within the HVAC, and the wiring isn't clear on the Jeep)

 

[DadOSix]

What year of jeep ? I suppose after 2005 the climate control changed?
My 2004 has 3 positions where the A/C wont run, thankfully.

You must be registered for see images attach

Can you post a photo of your control?

06 we got a separate snow flake button

 

[DadOSix]

Mines a 2002 so the same controls.
However, mine cycles in all positions.
There's definitely something strange with electrics as my ODB2 logger shows the voltage swinging rapidly between 11.5V and 13V with engine running. Not only is this varying much more than I'd expect but it's about 1.1V down on a direct measurement across the battery.

There're a couple of earthing points on the inner wing under/behind the battery tray that are really crusty.

^^^^^^^. right there is where i would start. clean that up and check the ground straps from firewall to the cylinder head on each side. an intermittent / bad ground (earth) will make your wiper motor stop at random.

She's got an MOT retest on Sunday, after I had to replace both rear suspension arms, so I'll wait to see how that goes before I get stuck into the electrics.

 

[Warpc0il]

I've fitted a thick cable directly from battery -ve terminal to engine ground stud on firewall.

A/C drive clutch now not hunting.
Wipers working fine
Voltage on OBD port stable and same as measured across battery.

 

[DadOSix]

I've fitted a thick cable directly from battery -ve terminal to engine ground stud on firewall.

A/C drive clutch now not hunting.
Wipers working fine
Voltage on OBD port stable and same as measured across battery.

so are we calling this ‘sorted’ then? Sounds like you have isolated the issue!

 

[Warpc0il]

Let's say "sorted for now" though I intend to remove/clean/replace all the factory earths in the engine bay, at some time in the future, as it shouldn't need my extra cable and something still might be compromised at present.

 

[Ksat]

Thanks for letting us know what the problem seems to be and here's hoping it stays fixed!