Help from the AC gurus

[Rookie2]

My AC is not blowing cold air and in fact it doesn’t appear the compressor is kicking on at all (hear no change in engine RPMs with AC on). One of the first trouble shooting items in the manual is to inspect the relays.

Questions:
1) does that sound like a likely cause?
2) to test the relays it says to “apply B+ between terminal 1 and 3” and test continuity between 2 and 4. What does apply B+ mean?

TIA

 

[rolliges]

More likely the refrigerant pressure is either too low (more likely) or too high (less likely).

Gain some knowledge, rent some gauges at an auto store, add refrigerant if needed. If so, should kick right up.

 

[Rookie2]

More likely the refrigerant pressure is either too low (more likely) or too high (less likely).

Gain some knowledge, rent some gauges at an auto store, add refrigerant if needed. If so, should kick right up.

So if the refrigerant is low, the compressor won’t kick on at all?

 

[Irish Reiver]

So if the refrigerant is low, the compressor won’t kick on at all?

If it is just a little low the compressor will tend to cycle on/off at a higher frequency but once the refrigerant drops below a certain threshold the compressor will not come on at all.

 

[Rookie2]

If it is just a little low the compressor will tend to cycle on/off at a higher frequency but once the refrigerant drops below a certain threshold the compressor will not come on at all.

Okay. Good to know. Thanks.

 

[ppc]

B+ = battery voltage

 

[elhombre]

The first observation you need to look for is if the compressor clutch is engaging when you turn the A/C on. When the A/C is off, and you look at the pulley on the front of the compressor, you will see the belt rotating around, BUT you will see the front plate of the compressor clutch NOT moving. Turn the A/C on, the front compressor plate will engage, and you see the entire front assembly rotating. The relay you are checking controls this action. So, does the compressor clutch engage and disengage? If not, then you move to the relay.

If I was a betting man, I would bet you a case of Corona it is low on Freon, and not the relay. Power will be stopped before the relay if the Freon is too low, or too high. Jumping it with B+ goes "around" these two safety switches, causing the compressor clutch to engage, and you see the entire front of the compressor turning.

 

[flintknapper]

On your '97, right in front of the battery on the high pressure (liquid line) there is a 'trinary switch'. IF the system pressure drops below about 30 psi...it will not allow the compressor to come on. The same is true IF the pressure is too high.

Whenever a compressor clutch will not engage....it is prudent to first determine if it is 'capable'. The compressor clutch is activated by a 'coil' so it's basically an electromagnetic clutch. IF the coil is shot (windings burned up or shorted out) the clutch will not operate. IF the 'air gap' is too large, it will not engage or will engage poorly.

Once it has been determined the clutch is (or is not) capable of engaging then you can move on to other possibilities.

Alternately, if you have a set of gauges, hook them up and see what your system pressure is. IF low or high (usually low) then most likely adding refrigerant will solve your problem. But if low, be aware....you have a leak. Refrigerants are not 'consumables' (like engine oil) so the only way for the system to be low...is because of leakage.

 

[Rookie2]

So, does the compressor clutch engage and disengage?

No, the magnetic clutch is not engaging.

Here comes the amateur hour questions..., I’m not much of an electrical guy but I’ve got an Ohm meter. So to test the relay, am I testing the actual relay or what the relay plugs into? And do I understand that “ B+” means I need to jump those two terminals and then check for continuity between the other two terminals? And, how do I jump them, just a paper clip?

Thanks again.

 

[1972FJ55]

I think you might be better served to get some gauges hooked up and see what the static pressure is. Far more likely to have lost some refrigerant than to develop an electrical problem.

 

[elhombre]

Paper clip used to jump between the terminals in the relay socket will work fine.

To check if the clutch is working, you must get 12 volts, B+, to the wire going into it. If it is working, you will hear it close/click when the 12 volts is applied to that wire. One end of that compressor clutch wire is in the clutch, the other end comes up to the bottom of that relay socket. With the relay out, you should be able to take a wire with one end on the positive side at the battery, and stick the other end down into the socket into #1 or #3. One of those terminals is the one that goes straight to the clutch. With out the wiring diagram in front of me, I can't tell you which one. But with the car off, no key in ignition, you should be able to test the functionality of the clutch with a jumper wire from the battery.

I'm 99.99% sure you must have the ignition on for the paper clip trick to work.

If the clutch clicks on and off with your jumper wire straight from the battery, you know it works. THEN , you move to why the power is not getting switched to it. Most likely it is because of the low pressure switch is stopping it. Low Freon.

 

[Rookie2]

I think you might be better served to get some gauges hooked up and see what the static pressure is. Far more likely to have lost some refrigerant than to develop an electrical problem.

10-4. Sounds like that is the most likely culprit.

 

[flintknapper]

I think you might be better served to get some gauges hooked up and see what the static pressure is. Far more likely to have lost some refrigerant than to develop an electrical problem.

Agreed. Lacking any previous history of an electrical issue...the quickest way to determine the most likely culprit (low or no refrigerant) is to hook up a set of gauges. He needs to see 40-50 psi (minimum) static pressure to satisfy the low pressure switch (trinary switch) assuming it is working. In any case....it would be a good starting point. If there is enough refrigerant (pressure) then we can go back to the clutch and on from there.

 

[Rookie2]

Okay. Ordered a set of manifold gauges.

FYI, I had my compressor changed back in 09. Just says Freon on the receipt. Is it fair to assume R134a was then and is now still the right refrigerant to use based on what the manual says?

 

[Rusty Marlin]

Yes, that's a fair assumption.

 

[ccslider]

alot of auto part stores will rent an ac sniffer to find leaks and some have gauges too

 

[flintknapper]

Okay. Ordered a set of manifold gauges.

FYI, I had my compressor changed back in 09. Just says Freon on the receipt. Is it fair to assume R134a was then and is now still the right refrigerant to use based on what the manual says?

Correct R134a

About 1.8 lbs (for a new recharge).

 

[whereyouare]

Wanted to chime on this thread as I am running into a similar issue.. I recently had my heater hoses replaced professionally and my AC stopped working all of a sudden a week later. Would this be correlated at all?

I checked my mixing valve and tried the trick there, it doesn't seem to work. Also, my compressor seems to run fine. When I went to recharge the freon, the gauge read 0 PSI, I gave it a few pumps and the gauge still read 0 PSI.

I'm stumped. It's supposed to be super hot in socal this weekend and I need that AC!

 

[flintknapper]

Wanted to chime on this thread as I am running into a similar issue.. I recently had my heater hoses replaced professionally and my AC stopped working all of a sudden a week later. Would this be correlated at all?

I checked my mixing valve and tried the trick there, it doesn't seem to work. Also, my compressor seems to run fine. When I went to recharge the freon, the gauge read 0 PSI, I gave it a few pumps and the gauge still read 0 PSI.

I'm stumped. It's supposed to be super hot in socal this weekend and I need that AC!

When you say 'recharge' do you literally mean fill from an empty system or just 'add/top off'?

Were you using manifold gauges or one of the recharge cans with a gauge? I'm sure we can help but we need a little background info. Generally speaking....working on the heater hoses would not have anything to do with your A/C not cooling ( save for the mixing valve being open).

 

[Rusty Marlin]

I'm not a guru, just a duffer; you need as set of manifold gauges to tell anything.

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A couple of these won't hurt either,

Digital Pocket Thermometer

While you may not know what to do with all the information gathered from those tools, the gurus do and can make intelligent decisions to move your project forward.
Good luck.