A/C Compressor not Engaging

[bigsky]

I have checked that the blue cable is moving the selector to the proper position to select A/C on the dash, but the compressor will not engage. I have checked the fuse, and the system has adequate psi. Any more ideas? Thanks.

[jawn101]

I have checked that the blue cable is moving the selector to the proper position to select A/C on the dash, but the compressor will not engage. I have checked the fuse, and the system has adequate psi. Any more ideas? Thanks.

The blue cable doesn't do anything electrically for the compressor, that's a 100% manual flap adjustment. Have you checked your low pressure switch on the accumulator? Do the radiator fans kick in when you select max A/C? Do the other mode switch settings work with the air coming out where expected? (Vent, bi-level, defrost, etc)

[bigsky]

The fans do not kick on. It appears that the other dash controls work properly. Where is the low pressure switch for the accumulator located? Is there another fuse, other than the one located in the cargo area behind the passenger seat? Thanks.

[Chris Burns]

Check your refrigerant level. The compressor has a feature that shuts it off if your refrigerant level gets too low.

[Ron]

Where is the low pressure switch for the accumulator located?
It's tucked in back of the front passenger side wheel well. You can jump its plug with a short wire, but only long enough for a test.

[bigsky]

What is the normal psi for the system? Is there a picture anywhere of the low psi switch. Thanks.

[jawn101]

What is the normal psi for the system? Is there a picture anywhere of the low psi switch. Thanks.

Switch is the round part in the center of top of the the accumulator....

http://www.specialtauto.com/delorean-parts/images/ac-accum-reference.jpg

#26 on the parts diagram...

http://store.delorean.com/c-303-7-2-0-refrigerative-system.aspx

Pressure will depend on if you are R134a or R12. What is your rest pressure on both sides? I'd bet you are low on refrigerant....

[Jonathan]

Mr BigSky sir, let's see if we can solve your problems. We all are driving really similar cars, and out of 9,000 of them around, I can think of at least one other that has had the same troubles as you're describing. Mine :)

That picture of the accumulator in the front right wheel well, if I remember correctly, where you see that criss-cross X, the two plugs are for the high pressure cut-off and the low pressure cut-off. Like Jon said, the one on the top of the accumulator is the low (the one you want to jumper), and high one is on that X right beside the relief valve. It really is straight forward to jumpering it. You just need to wiggle the connector off (they tend to be pretty snug). Try not to pull the wires right out of the connector. Then once you have the connector off, you'll see that it is just two spades, male ends on the switch and female on the connector (I think... my car is 3,400 km away at the moment). Stick a short jumper wire from one female spot to the next.

Now, just to add to what Ron said about doing a short test. You can actually do this with the engine off. All you really need to do is put the key in the ignition and turn to accessories and that will power the clutch on the compressor if you have the HVAC mode switch turned to MAX for example. If there is a sound out there that is best described by the word "clack", then your compressor clutch engaging is it. If you have the key at accessories, turn the HVAC switch to AC, you will hear the clutch "clack" in (it pulls in towards the compressor). If you have a helper with you, you can actually watch it and see it clack in from the rear of the car.

So, does your compressor clutch engage during this test? My guess is it won't. Why? Because I think it might have a problem that might just be similar to what I had on my car a few years ago. And that is that it's not going to engage because something is not right in the wiring. The clue is when you said your fans don't come on when you turn the mode switch to AC. That's when they are supposed to come on even if the AC isn't working (I think, someone double check that theory).

When I first got my car, the fans never came on. This wasn't a big deal until August in Ontario came around and the breeze of the road wasn't enough to cool my car down. When I came close to overheating one day waiting for a spot at a gas station, I knew I had to get to the bottom of it. I believe back then it was a combination of Ron and the Dave's who helped me figure out that there was something loose on the underside of the relay tray. What I found was that if you are looking in your fuse relay area and see where the relays plug into the sockets, the wires terminate under those sockets. When the relay pushes down, it has the potential to push the wires out on the underside. This is what happened in my car. Check your fan socket and maybe the others too and if you feel something isn't in there well, snug it up. What you should be seeing is that your fans should come on when you turn it to the MAX setting regardless of whether the clutch kicks in (I am pretty sure that's how it is supposed to work, others can confirm maybe?).

Once you can reliably get your fans to come on, then see about getting the clutch to clack. If it still doesn't, you might have some sort of electrical problem still. I would then guess that if you jumper the low switch and get it to engage, then you're due for a freon recharge and there's plenty of ways to approach that.

Sorry for the essay. Hope that helps :)

Edit: Here's a picture of the relay socket. It's not a great zoom in, but gives you an idea of the socket and wires underneath.

10393

[jawn101]

The clue is when you said your fans don't come on when you turn the mode switch to AC. That's when they are supposed to come on even if the AC isn't working (I think, someone double check that theory).


Jonathan - unless the fans are supposed to be on via the otterstat already, they should cycle with the compressor. I just went through a similar process trying to tweak my pressures and pulled the wiring to the low pressure switch many times with the A/C running. The compressor will disengage and the fans will shut off simultaneously when the low pressure switch trips unless, as I said, the otterstat is already engaged. At least on my car! :lol:

[Jonathan]

Jonathan - unless the fans are supposed to be on via the otterstat already, they should cycle with the compressor. I just went through a similar process trying to tweak my pressures and pulled the wiring to the low pressure switch many times with the A/C running. The compressor will disengage and the fans will shut off simultaneously when the low pressure switch trips unless, as I said, the otterstat is already engaged. At least on my car! :lol:

Ya know, you're refreshing my memory. It's been a few seasons since I've done the low pressure switch jumper test.

I think what will happen is if you have the switch jumpered, the signal is that freon pressure is good, and the compressor could be kicked on when called for. Then, if you select to MAX AC, you should see the fans come on. Either the otterstat tells the fans to turn on when the coolant temp is too high OR, the fans come on anytime the AC compressor is called on. I think that is why I have heard the advice that if your car is close to overheating, you turn the AC on so to force the fans on.

For BigSky, if he is able to jumper the switch, and gets the fans to turn on when in MAX AC, we can rule out a fan wiring problem. If they don't kick on, then there is something more to the story.

Thanks for clarifying Jon.

[jawn101]

Ya know, you're refreshing my memory. It's been a few seasons since I've done the low pressure switch jumper test.

I think what will happen is if you have the switch jumpered, the signal is that freon pressure is good, and the compressor could be kicked on when called for. Then, if you select to MAX AC, you should see the fans come on. Either the otterstat tells the fans to turn on when the coolant temp is too high OR, the fans come on anytime the AC compressor is called on. I think that is why I have heard the advice that if your car is close to overheating, you turn the AC on so to force the fans on.

For BigSky, if he is able to jumper the switch, and gets the fans to turn on when in MAX AC, we can rule out a fan wiring problem. If they don't kick on, then there is something more to the story.

Thanks for clarifying Jon.

No problem! Summer is approaching and I bet every. single. one. of us is scrambling to get our A/C in top shape so we don't end up with rolling stainless caskets.

BigSky (if that is your real name!) - you could also help us rule out fan wiring by jumpering your otterstat and seeing if the radiator fans come on.

[Ron]

What is the normal psi for the system?
If you mean while the system is not operating, it's one of those "That Depends" things ;-)...it is around 70psi when the ambient temp 70F -- But this doesn't tell you a lot because the refrigerant's properties are such that one, two, or three cans will read the same if allowed to sit long enough to reach the ambient temp.
You should get a set of gages and the system running then use this chart (For R12):
http://dmctalk.org/attachment.php?attachmentid=3778&d=1313480720

+1...The Otterstat can turn the fans on independently -- Power from the Mode Switch must go through the Low Pressure Switch before reaching the Compressor Clutch (All modes!).

Momentarily jump the Low Pressure Switch with the AC on. If the compressor does not engage, see if one side of the plug has 12V. If not the problem is toward the mode switch. Otherwise it is toward the Compressor (try momentarily applying 12V to its pigtail connector)......

[bigsky]

First off I want to thank everyone who has posted here giving some great advise!! For starters I jumped the low pressure cut off switch and the fans came on. I was told the the system had been changed to 134. I grabbed my 134 can and checked the psi on the system it was low, about 25 psi. I began filling/charging the system and the compressor would kick on at about 45psi, and run for about 6 seconds until it got to 25psi and shut off. I could also feel cold air coming out of the vents. Does it sound like I just need to add more 134? What should the max psi be. Thanks guys!

[DMCMW Dave]

First off I want to thank everyone who has posted here giving some great advise!! For starters I jumped the low pressure cut off switch and the fans came on. I was told the the system had been changed to 134. I grabbed my 134 can and checked the psi on the system it was low, about 25 psi. I began filling/charging the system and the compressor would kick on at about 45psi, and run for about 6 seconds until it got to 25psi and shut off. I could also feel cold air coming out of the vents. Does it sound like I just need to add more 134? What should the max psi be. Thanks guys!

Probably still low. The high side should hit 200-250psi at cutout depending on the air temperature when you are doing this. Cycle time will vary from 10 seconds (at 2000 rpm with the fan on low at 70F) to infinite (at idle) with the fan on speed 4 with the air temp at 80 or above. It has to cycle or it won't work, but running constantly at idle under some circumstances is normal.