On my 1992 XJ6, the AC compressor was locked up. I have another Sanden compressor from a 1989 XJ , that did not come with a Superheat switch. In place of the Superheat switch there is a plug. This is a good AC compressor. The clutch power connector was larger so I retrofitted the correct size clutch power connector from the old one.
I tried to install the superheat switch from the locked up compressor to the one from the 1989 but the hole is of a different size.
Can I use the compressor without the superheat switch without having an issue with the exception of if the AC system is low on freon the compressor will not shut down. (I am willing to live with that).
Because the old compressor locked up, I dismantled and flushed out the system, replaced the dryer, expansion valve and all of the O-rings.
Since the superheat switch is not installed, do I have to jumper the the connectors that went to the superheat switch in order for the compressor to work?

At this point in time, I do not know if the AC controls work or not because I have the interior gutted for a thorough cleaning.

AS AN ASIDE
(I took the Center console apart to replace the plastic piece in the J-gate assembly which was broken due to a faulty gear shifter cable.
Apparently, the PO had an electrical issue(which I found, faulty ground). This fried the shifter cable and the harness for the NS switch located at the transmission.
I was able to repair the NS switch harness,installed a new shifter cable and fixed the ground issue).

Back to the topic of the AC:
Beside the question regarding the superheat switch, what else should I be looking at in the system to make sure everything is OK prior to me putting the interior back together?
Thanks in advance for any inputs.

 

Ha! That's literally the exact same situation I'm dealing right now with my '92. The compressor mounting is such a PITA, and my rebuilt compressor had stripped threads for the pressure switch which were leaking over time... I had saved the original compressor, so I removed the bolts securing the head, cleaned it up, swapped over the new valve plate (or whatever it's called) and installed it on the compressor still mounted in the car. My newly rebuilt compressor is kind of a Frankenstein at this point.

Those darn low-pressure cutoff switches leak if you look at them wrong... The "original" switch is about $50-75. Generic replacements are under $10. I'd really like to install a fitting with a shrader valve in that port on the compressor to use a screw-on type low pressure switch, the kind newer cars use on the refrigerant lines themselves. That way you don't have to evacuate the system if it needs to be replaced. I'm still running R12 and it's not cheap...

I am waiting for my in the mail now. I'm hoping it wont be too big and interfere with any of the other fittings.

Jumper the two female spade connectors and the clutch relay will activate as long as the Climate Control system is energizing it. Be careful tho. Loss of freon means no oil will be moving through the system and you could seize the compressor up and spew metal shavings all through the system... Not good!

-Nick

 

One more question.
If the 1989 XJ40 did not use the superheat switch, what safety device did it have to prevent the compressor from self destructing in the event of a loss of refrigerant.
I have been searching the manuals for an electrical schematic for the 1989 XJ40 to no avail. I will continue to do some research. I have looked at the AC hoses to see if the switch was mounted there but found none.
From what I know, on my 1985 Series 3 the AC compressor does not have a superheat switch either. The electrical connector is just hanging there.
I have been using the AC like that for over 3 years. I monitor the vent temperature with a digital thermometer all the time while in use.
I am in Florida, and this morning at around 7 a.m. with the ambient temperature around 78 degrees and no humidity, I was travelling on I95 at 80 mph and I saw the vent temp at 31 degrees. On my return trip at around 11 a.m. with the ambient temperature hovering around 90 degrees and extremely high humidity, same speed, the vent temperature was around 49 degrees. Very comfortable inside car.

 

89 also had a "High Side Low Pressure Cutoff Switch" located at the "AC Compressor, Rear"

It should be noted, though, that the rebuilt compressor I received had two plugs installed, no switch. That's when I found out the threads were stripped, when I removed the plug to install the pressure switch... I figured it was tight enough with an oring but it eventually leaked. Maybe it was a replacement and nobody bothered to install the switch?

The 93+ cars have a pressure switch installed on a service valve on the refrigerant line. A MUCH better setup.

Attached is the electrical diagram for the 1989 XJ6 A/C compressor clutch circuit.

Also, from mid-86 and on, the Series III had the superheat switch deleted, and used a low pressure cutoff switch at the back of the AC compressor as well.

-Nick

 

As an aside, I've been reading some mid-90's GM literature on R-134a retrofitting, and apparently some vehicles, mostly trucks, required the addition of a pressure switch once the system was converted to R-134a. GM's solution was a Saddle Valve Kit (part # 15985307), which is a 2 piece valve which pierces the refrigerant line. There's a shrader valve, and the pressure switch screws onto the valve. They also make the same type of kit for a service valves.

This could be a useful way to add low-pressure protection for those of us that have plugs in the compressor or issues with stripped threads, or with the correct switch, it could even be a way to trigger the electric cooling fan relay based on A/C pressure much like 93+ cars. I really, really like the fact that a service valve like the GM-one would allow for switch replacement WITHOUT having to evacuate the entire system, which is required for compressor-mounted switches. This is a big deal for people like me who are running R12.



For fun, I just ordered one on eBay for less than $5 shipped, in the box with directions.

Nick