I have an 86 with Delanair mk 2. There is no pressure in the A/C circuit and of course the compressor does not kick in. I was wondering if I can check compressor functionality by jumping the pressure switch? If so, where would it be on my model year?
No pressure switch on your '86ā¦unless a PO has changed things around
You can engage the compressor clutch by simply applying power and ground to the connector at the compressor itself. Itās just a electro-magnet type of thing. I wouldnāt do so for more than a few moments without knowing if the system still has oil.
Cheers
DD
Does that mean it would normally run all the time, even though there seems to be no refrigerant in my system?
No.
There were two types of circuits used to protect (that is, disable) the compressor in event of freon loss.
Until 1987-ish, a āsuperheatā switch was used. When freon was low the switch closed and grounded a three-prong āthermal limiter fuseā. The fuse would blow and open the circuit.
Later cars used an āHSLPā switch (High Side Low Pressure). When pressure dropped the switch would open, break the ground circuit, and disable the compressor.
Both switch types are mounted on the rear plate of the compressor.
Your car should have the Superheat system but sometimes compressors are replaced with the āHSLPā type
Cheers
DD
Hi Doug,
Thanks for the reply. Got it now. So if I plan to re-pressurize and re-commission the system, Iāll need a new thermal fuse. But first Iāll test that the compressor kicks in when I ground the ground wire.
Mark,
I also recommend that you replace the receiver drier and all the o-rings in the system and check that your A/C system will hold about 30 in Hg of vacuum for a few days before you have the system recharged with refrigerant. The vacuum test will identify if you have a leak under vacuum and increase the odds that your system wonāt have a slow leak after servicing. Of course the real test is if it doesnāt leak and provides cooling air for an extended period of time once serviced with refrigerant.
This is how I returned the A/C systems in two of my Jaguars (1987 XJ6 VdP, 1990 V12 VdP) to running condition in the past year. One of the compressors leaked under vacuum and I removed and replace it with a rebuilt one. I am working on the A/C system in my third Jaguar (1984 XJ6 VdP) now and hope to get that A/C system working again in the next week or two. Yep, I replaced that compressor as well because it leaked vacuum.
Paul
This doesnāt really confirm much about the condition of the compressor. It only confirms that the clutch works. And, really, you could test that without the engine running, just connect up 12V to the clutch and watch to see if the gap between the discs closes and whether you can turn the compressor by hand.
1 Like
sound advice in my opinion. Several times I have had to have my A/C system āfixedā that turned out to be bad seals/o-rings. Although thatās the good news (no expensive parts to replace) the dog-gone refrigerant aināt cheap.And the a/c shop owner I know says replace the receiver-dryer is good practice
Thanks for the thoughts everyone. I hadnāt considered that evacuating the system myself was an option. But cheap a/c vacuum pump kits abound. One for 82.99 on EBay. Would one of those be good enough just to check the system holds vacuum? Then I could get it filled at a shop.
Replace the receiver dryer and then take it to a professional.
I just tested the clutch. One side has 10V on it with ignition on (green wire). Thatās a bit odd, was rather expecting 12V. I grounded the other pin, no click from the clutch. So now I guess Iām wondering if thatās because the clutch has failed, or if itās because 10V is insufficient for it to work properly.
Please ignore the last post. The voltage was 10V because the compressor clutch was engaged. If I disconnect the two pin plug, thereās a click and the voltage on the green wire jumps to 12.5V. Clutch engages with two-pin plug connected, disengages if I pull it. Good.
Thereās definitely no refrigerant in the circuit, so I wonder why the thermal fuse didnāt blow. I hope no damage has been done to the compressor. Hopefully thereās enough oil left in there.
Put a new dryer in, and took it to a shop, where they vacuum checked the system. No leaks under vacuum. But when pressurized with compressor running, thereās a big leak from the compressor.
Looks like you need a new compressor. BTW, itās not all that unusual that an AC system will hold vacuum, but leak under pressure.
Forces applied from opposing directions to the same seal can produce different results.
Did he tell you where itās leaking? The o-ring in the output block on the back is a common source and easily replaced. The big o-ring that seals the rear isnāt too bad either. Same for the front shaft seal.
The leak is from the rear. Not from the two O rings where the input and output attach, but slightly forward of those, where the mounting plate attaches to the round part of the compressor. Is this where the big O ring is? Iāve already ordered a re-con compressor from Rock Auto but it would be interesting to know whatās wrong.
Right, thereās a big o-ring that goes around the perimeter where the rear cylinder head attaches to the housing (four studs/nuts). But thereās also an identical o-ring under the front cylinder head, and several small ones inside (and of course the shaft seal). So I think you made the right decisionābest to reseal the whole thing, which is what you get in a rebuilt compressor. IMHO.