AC Trouble shooting

yar02169

yar02169

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Joined
Apr 12, 2012
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40
Replaced bad compressor 2 years ago, and all was good. AC is dead again. Coil reads 3.6 Ohms. I've tried to push on the clutch, but it doesn't move in when running or off. How hard is it to push the clutch in? Is it possible to measure voltages coming to the compressor to narrow down whether it's the compressor or the automatic control unit? Low pressure switch has been replaced, jumping it does nothing. Any ideas?
 
yes...get a meter and check the voltage AND ground coming towards the clutch.... just unplug the connector and measure things. Nothing special, its basically a solenoid.
 
what brand did you buy?
you check freon levels? You did use oil during your install?
 
The unit was a low mileage (80k) junkyard part. I had a friend discharge and recharge the system, vaccuum, oil and freon added using a professional system.

Silly me, I checked the Ohm;s, but didn't check for voltage heading to the coil. I guess I have a chore for this afternoon.

It's one of two vehicles, more of a fowl weather vehicle. Miles don't add up these days, but it was fine for some 18 months, then kaput.
 
Well, I would say that there's no voltage going to the coil. Meter reads 0.179 volts. All fuses are good, so my guess is that it's the head unit.
Any clue as to whether they can be repaired?
 
I wouldn't suspect the head unit until you triple-checked underhood fuses 22 and 30 with a meter while they're powered up, and swapped relay 44. How did you check the fuses? (Visually doesn't count for a lot.)
 
Well, since the system was fine before I swapped compressors, I figured maybe the hose connector isn't tight enough, or something got scored and that's where the leak could be. I disconnected the hose, and when looking, I saw my problem (most likely). There are two rubber coated, probably collapsable washers, one for each hose.

Went to Autozone, bought a complete o-ring and washer kit for the entire AC system, at $5 it's worth it for the two washers. I put the new washers in, tightened things up, and will see my friend this week to get some freon in there after a vaccuum check. I should be good now that the seals are new.
 
System vaccuumed/recharged. No compressor operation. Fuses and relay checked with a meter, then switched with other Fuses and relay. Used a stick to push the clutch, jumped the low pressure switch. No voltage going to the clutch.
Baffled and looking for direction...
 
How did you check the relay with a meter? While plugged in and power applied? No way to functionally test a relay with only a meter.

Is the coil being energized and the output terminals aren't sending power to the clutch, or is the coil not getting a good control signal?
 
yar02169 said:
System vaccuumed/recharged. No compressor operation. Fuses and relay checked with a meter, then switched with other Fuses and relay. Used a stick to push the clutch, jumped the low pressure switch. No voltage going to the clutch.
Baffled and looking for direction...

Not sure, but this is rather confusing. How did you recharge your system with NO voltage going to the clutch and thus had no compressor running.

Further, even though you did "some form of testing of the relay", IS it operating? IF it isn't operating, you aren't going to get any voltage at the compressor.... which you probably know. Then, you need to check that there is voltage at the relay (actually two voltages) AND a ground coming from the PCM to the relay at the appropriate time (ie. when AC is selected). NOTE: the PCM will not allow the compressor to operate IF your pressures are not in the proper range.... although you can "jump" the compressor for a short period to see if it is functional as a "last resort".
Click to expand...
 
Thanks for the replies.

Since all of the relays in the fuse box have the same number, I have swaped the relay around to other positions, and put a different relay back. I will check for voltages, and ground this afternoon, what should I expect to see for the 2 voltages?

The system was charged with a professional recovery, vaccuum, charge machine. Freon was added using the vehicles sticker that said it needed around 1.8 lbs of freon. Oil was also added per label requirements.

The machine only mentions turning on the system after it had filled the system, the compressor isn't used to fill the system.

The coil itself reads around 3.6 Ohms. The voltage to the coil is just about zero, 0.17V or so, so what I would say is no voltage.

With the system now charged, I tried to push the clutch with a wodden dowel, but it won't engage. The gap between the clutch and pulley loks to be maybe .020" at the most, no beig gap and about where I believe it should be.

With the engine running, I have turned the temp knobs from cold up to hot, and the system responds as one would expect. The blower goes from Max down to Min, and when turned down again, the fan speeds up.

I hope this helps you help me.
 
Something I would do is check the voltage away from the connectors, starting with the cycling switch...
 
Swapped out the low pressure switch, I have the original from before the compressor change. Still nothing, and a jumper does nothing.
On to the relay. Using a trouble light, and the relay unplugged slightly. The "7" and the "O" have a bright light while the "8" is dim, and nothing in the last corner. This is with the light connected to ground. Using a meter, it reads zero, zero, zero and 12V respectively.
With the test light, when checking the "8" there is a click from the relay.

The photo didn't upload from my pnone. My refrences were from the markings on the relay.
'7' is towards the front, engine side.
'8' is towards the rear (firewall), engine side.
'O' is towards front, fender side.
'Other Corner' is towards rear (firewall), fenderside.
 
Used the test light as a power source. Connected one end to the battery, the other went to the red lead going to the coil (only unplugger the red wire, left the black alone). Power straight to the coil did nothing but light the test light. That means the coil is not Open, and with my prevous Ohm reading, it's not a short either.
Why do I always get the difficult problems....
 
hmmm... I am not an AC guy but have seen AC work done a few times. Are you doing the servicing with the equipment or is someone else doing it for you. If it is you, are you using the equipment correctly... is it possible that the charging was not successful / incomplete.... most times that I have seen the operation, the engine / AC is run to complete the process because of pressure issues between the charging apparatus and the AC system.

As far as your test with the light, I don't think that provides you with much other than you knowing that you sent 12v to the relay.... but the circuit always has 12v going to it.... its the ground that the pcm sends that you need for the relay operation.

oops... I guess you were referring to the clutch "coil".... my misread.
 
yar02169 said:
Swapped out the low pressure switch, I have the original from before the compressor change. Still nothing, and a jumper does nothing.
On to the relay. Using a trouble light, and the relay unplugged slightly. The "7" and the "O" have a bright light while the "8" is dim, and nothing in the last corner. This is with the light connected to ground. Using a meter, it reads zero, zero, zero and 12V respectively.
With the test light, when checking the "8" there is a click from the relay.

The photo didn't upload from my pnone. My refrences were from the markings on the relay.
'7' is towards the front, engine side.
'8' is towards the rear (firewall), engine side.
'O' is towards front, fender side.
'Other Corner' is towards rear (firewall), fenderside.
Click to expand...
are these measurements with key in "on"? the "0,0,0,12" don't look right. there should be two 12's. One for powering the relay coil and the other to be switched thru to the compressor clutch.

"does nothing" is this with a jumper directly to the clutch / compressor?

DK GRN going to the clutch is power (on my reference), BLK is ground and LT GRN is status (for the automatic climate control system...which you have right?)
 
@ Budwich
It does confuse me. All measurements were with the engine running. With the test light, I got 2 bright lights and a dim one (that also clicked the relay). The meter only showed 12V at one point. I was thinking it's more like a 5V and a 12V source, if it should be two 12V sources, I'll have to go back and re-check it.
Knowing the dark green at the coil connector is power is good to know. Do you have any idea where that leads off to? Is it in the massive connector next to the power distribution box under the hood?

I clipped one end of the test light to the battery, and the other to the red wire going to the coil, figuring a direct power would make it work, but it did nothing but light the test light.

I didn't do the system refill, my autobody friends have the machine and were nice enough to hook me up. The rest, well it's up to me to figure out...
I'm handy and have done lots of engine work, A/C is a relatively new venture, did a bearing replacement on my other car last year with great success.
 
"I clipped one end of the test light to the battery, and the other to the red wire going to the coil, figuring a direct power would make it work, but it did nothing but light the test light."

Not sure what "red wire" you are referring to. I don't see it in the circuit... maybe "mis info" in my reference.

I don't thing that you can use your test light as a "jumper"... it has stuff in it for doing the lights.... kind of like trying to use a meter (set on voltage) as a jumper.

I don't know how the compressor wiring is routed as reference is only a schematic not cabling.

Perhaps you aren't using a KNOWN ground for your measurements.... but there has to be two voltages going to the relay. One is fuse 22, the other fuse 30. Pull the relay to make sure that you are making good contacts with the pins in the fuse block.
 
I am just a amateur (shade tree), but I have never seen a system recharged with out
the compressor in operation for the final fill.
 
Time for an update.

Bought a reman compressor from Ebay, put it in, went to an A/C & Radaitor repair place for a charge. More primative than my autobody friends (no vaccuum), but more knowledge about A/C's. Popped in a charge, and the compressor didn't move. We re-checked fuses, swapped the relay around, still nothing. He went to see if he could jump the low pressure switch, and when he touched the wires, the compressor kicked in. Low and behold, it was a broken wire in the approach to the connector at the switch. One thing that was noticed was that the compressor was slipping and not running at engine pully speed.
He suggested repairing the broken wire issue, then he would finish filling the system and maybe the faulty connection will get the compressor running properly.
Went to a bone-yard, found a Bravada, cut out 18" of the lead wire to the low Pressure switch, and grabbed the switch while I was there, just in case.
Soldered in the 'new' connector and the compressor kicked on right away, without having to play with the wires. The clutch was still slipping.
Went back to the guy, he tossed on the gauges, and with the system topped off, it was still slipping. He recomended that I go back to the old compressor since the problem was not the compressor, but a broken wire. Before putting the old compresor back in, I took a look at the clutch. Removed it and cleaned the rust from both surfaces. Re-assembled and tested it, It pulled in, but wasn't that strong, so I took out the one spacer and tried again. This was now a good, solid, pull and when the pully was turned, the compressor did also. Air gap is tight, around 0.15", but free when not powered up.
Went to switch the compressors, and checked the air gap on the reman. compressor as it sat in the truck, the range was from 0.015 to 0.036", which explained the odd look as it ran, and the fact that it was slipping. Switched them and went back to my friends for a charge, and then it was happy dance time, as it worked!
Returned the reman compressor for a refund, no hassle due to the bad clutch.
All this work for a crappy broken wire, although I guess the clutch needed a little TLC in the near future either way, but what a pain it's been trying to figure this out. I had swapped out the low pressure switch during the trouble shooting process, but the engine was never running then, so when I moved the wire at that time, it never engaged the clutch.
Oh well, lesson learned, and maybe one of you will benifit from my challenge.
 
Thanks for the update. I find it hard to believe an AC place that knows a lot, would fail to invest in a vacuum. Without one, he can't check for leaks except by wasting a lot of refrigerant, and can't get atmospheric moisture out of the system that has a reputation for clogging the orifice up later. If it's possible, I'd love to know how he responds to those questions.
 
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