XJ6 & XJ12 Series I, II & III 1968-1992

A/C Clutch won't disengauge

 
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Old 05-13-2019, 08:17 AM
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Default A/C Clutch won't disengauge

I've troubleshot this till I'm blue in the face. I have to turn to the Village now. I'm fairly savvy at electrical stuff but this one is throwing me. I've replaced the A6 compressor, new dryer, new condenser, new Expansion valve, all new barrier hoses. Evacuated system, filled with R134A to proper amount with proper amount of PAG oil. And giving me all the right HI and LOW side pressures. And actually the A/C blows low 40's F. But... the compressor clutch never dis-engauges. Unless I turn the MODE switch to OFF. So far with all my testing the servo seems to be doing its job. I've read and can see on the wiring diagram that the in car temp sensor (tested ok) and the Ambient sensor and the Rancor are all in place and part of the compressor clutch picking. The amplifier has been replaced at one time or another with a cylinder looking one. Anybody have a better understanding and can aim me in the right direction - would be much appreciative. Thanks, Bill


 
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Old 05-13-2019, 08:59 AM
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The system is designed to keep the compressor engaged at all times, even in heating mode.

There are two scenarios that will disengage it:

1) Turn mode switch 'off', as you mentioned
2) Evaporator ice-up, as detected by the "Ranco" thermostat....which cuts the circuit

Cheers
DD
 
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Old 05-13-2019, 09:07 AM
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There's got to be a 3rd scenario (and maybe more). When the temperature in the car reaches what's dialed in on the temp switch. I just can't figure out that circuitry.
 
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Old 05-13-2019, 09:09 AM
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WOW! Just re-read your first line. REALLY?! On all the time? Then there's nothing wrong and I'm doing all this troubleshooting for NOTHING?
 
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Old 05-13-2019, 09:57 AM
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Not on all the time... The Ranco thermostat measures the temps on the evaporator and cuts out the compressor. This is what causes the compressor to cycle. If the evaporator gets too cold it will ice up and create a dangerous condition. The Ranco is located on the Right hand side of the heater box and has a few yellow wires going to it. Try raising the idle when the vent temps get low enough the compressor should cut out. The Ranco has a small flat blade adjustment screw. You could adjust it up for testing purposes. Since you're running R134A in a older system I'd set the Ranco adjustment temp a bit higher than for R12 so the pressure on the high side stays below 250 PSI
 
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Old 05-13-2019, 10:34 AM
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Is the Ranco the only thing that will cycle the compressor? I thought it was a protection device? And that other circuitry monitoring the actual temp inside the cabin that would cycle the compressor? Not trying to be argumentative, just trying to understand.

Thanks, Bill
 
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Old 05-13-2019, 11:20 AM
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Originally Posted by yachtmanbuttson View Post
Is the Ranco the only thing that will cycle the compressor?
Yup

I thought it was a protection device? And that other circuitry monitoring the actual temp inside the cabin that would cycle the compressor? Not trying to be argumentative, just trying to understand.

Thanks, Bill

The system is designed to run the compressor regardless of cabin temperature. If the cabin is at -10F and you turn the system on to heat the cabin, the compressor will engage. The idea is to refrigerate all incoming air and then heat it as needed. This is to dehumidify the air.

Cheers
DD
 
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Old 05-13-2019, 12:58 PM
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Maybe I'm being thick headed, but... what is the function of the in-car sensor and the ambient sensor. What actually controls the maintenance of a specific temperature inside the cabin?
 
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Old 05-13-2019, 01:24 PM
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I don't see any adjustment screw on the Ranco?

 
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Old 05-13-2019, 08:31 PM
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Originally Posted by yachtmanbuttson View Post
Maybe I'm being thick headed, but... what is the function of the in-car sensor and the ambient sensor. What actually controls the maintenance of a specific temperature inside the cabin?



Cabin temp is maintained by blending the refrigerated air with heated air. In max cooling mode no blending takes place but in all other modes, the incoming refrigerated air is blended with heated air.

The in-car sensor (above the glove box) measures cabin temp. The ambient sensor (at inlet to the RH blower) measures the temp of incoming air. The amp takes these readings, compares them to the desired cabin temp as set on the dial, and commands the servo to operate the switches, flaps, and valves accordingly.

Cheers
DD
 
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Old 05-14-2019, 02:56 AM
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I agree with Doug on this. The compressor clutch engagement is not temperature dependent.
 
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Old 05-14-2019, 08:20 AM
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Okay. I'm slowly coming around. It's so unlike every other car I've every owned where the compressor clutch cuts in and out periodically to maintain cabin temperature. So what else is new? Jaguar marches to a different drummer. Then... I'll assume the A6 compressor will handle a 100% duty cycle? And... I have to undo my wiring whereby I have the two electric cooling fans coming on whenever the A/C clutch is on. Because they will be on ALL THE TIME also. Darn! As I have done away with the viscous fan, nothing will be moving air through the condenser & radiator when the A/C is on. And... the fuel economy is that much worse with the compressor drawing all that HP.
 
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Old 05-14-2019, 10:01 AM
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For that very reason, Bill, I repurposed the window power cut-off switch on the ski slope to turn off the compressor as desired. The Light Green wire that activates the compressor relay (which activates the clutch) that goes between the servo and the relay that's out on the compressor, is interrupted by the switch.



So, power from the servo, must first go through the switch before it goes to the compressor relay.
This works well, and I can turn off the compressor any time I choose.
(';')
 
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Old 05-14-2019, 11:12 AM
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Great idea, butI don't see any compressor relay in any of the schematics???
 
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Old 05-14-2019, 11:14 AM
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But... I could certainly wire it at the output of the Rancor.
 
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Old 05-14-2019, 12:12 PM
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AC understanding is not my strong suite. Systems vary. Simple to complex. Think of the knob in other critters that selects shades of blue vs red. No blend. Just choose degrees of cold or hot. My Jeep is that way. It does have a compressor on/off button.

As did a long gone Olds Achieva. Son borrowed it once and complained of lousy AC.
I pointed out the on/off !!! Oh????

Carl
 
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Old 05-14-2019, 02:56 PM
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I think it is true to say that most if not all climate control systems keep the air-con part running all the time to dehumidify the air before then heating it, (if needed) to maintain the selected cabin temperature. It was like this on my two previous X350 cars and also on my current XE, I believe the cars prior to my X350, a Rover 75 was the same. In fact, not only does the air=con part run all the time, so does the heater matrix remain constantly hot, and flap valves maintain temperature by blending hot and cold air appropriately.
 
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Old 05-14-2019, 07:32 PM
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I agree with Elinor, add a discrete on/off switch to break the wire that goes to the compressor. Then on those nice drives in the evening you can switch it off. I also added a switch that forces the fresh air vent open and one that shuts off the water valve. So I have fully automatic plus the option for total manual override so I can make it do exactly what I want.
 
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Old 05-14-2019, 09:48 PM
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Originally Posted by yachtmanbuttson View Post
Great idea, butI don't see any compressor relay in any of the schematics???
Hmm. I would think ALL compressor clutches required a relay. I can't imagine all the required power to activate the clutch being sent through that flimsy ignition switch.

However, it wouldn't be the first Better Idea Lucas had, now would it.
(';')
 
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Old 05-18-2019, 07:33 AM
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I'm trying to find the video of the guy who showed taking apart his Delinair. He starts the video out flashing a joking the video is about his Ferrari, or some such, then flashes back to his XJ6. I think he then takes apart the center console to get at the Mode switch and I think removes the servo. Anyone know what I'm referring to?

Thanks,,Bill
 

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