Weird ac issue

[killj0y]

Ok so yesterday on the way to work ac was working great as usual. Halfway there though the compressor shut off. Later that day I jumped the low level pressure sensor to diagnose it. The ac clicked on and worked great, i picked up a new one and swapped them out and the ac worked great again. Just to be sure I threw on the gauges and the levels seemed fine. Well again this morning halfway to my way to work it shut off. The compressor can be jumped via shorting the switch harness and it works great. Is it likely I got a bad switch or is there something else I can check? There is no evidence of leaks and the gauges read fine. Any thoughts?

 

[Earl43P]

There is actually nothing weird about that symptom.

Here's what I think.
Your compressor clutch has worn out.

The clutch is actuated by an electromagnet.
Once the system has been operating for a while, the compressor heats up and so does the clutch. That heat creates greater resistance in the electromagnet's circuit, powered as you already know, through the low pressure or "cycling" switch.

With a worn clutch, the air gap in the clutch is too great for the now weakly powered clutch coil to overcome.

Each time you went to troubleshoot it, it had a chance to cool down enough to start working again.

If you'd like to prove this theory, cut some stranded copper wire. Twisted wire works well because it won't fall out. Use the wire to shim the clutch gap closer.

When you look at the clutch, you'll see the 3 finger straps that attach the two parts of the clutch. That is what you shim. Close up that air gap a bit and it should continue to work for years to come. Or, you can replace the clutch (new are big $, but you can usually find one at the junkyard for cheap).

http://www.autoacforum.com/messageview.cfm?catid=2.&threadid=14277

You'll note in that link that they talk about a shim washer on the clutch. Same idea (better actually) but installing it there means you have to get the compressor clutch off of the compressor. Getting that nut to break loose can be a problem, which is why I use the wire on the fingers.

 

[killj0y]

There is actually nothing weird about that symptom.

Here's what I think.
Your compressor clutch has worn out.

The clutch is actuated by an electromagnet.
Once the system has been operating for a while, the compressor heats up and so does the clutch. That heat creates greater resistance in the electromagnet's circuit, powered as you already know, through the low pressure or "cycling" switch.

With a worn clutch, the air gap in the clutch is too great for the now weakly powered clutch coil to overcome.

Each time you went to troubleshoot it, it had a chance to cool down enough to start working again.

If you'd like to prove this theory, cut some stranded copper wire. Twisted wire works well because it won't fall out. Use the wire to shim the clutch gap closer.

When you look at the clutch, you'll see the 3 finger straps that attach the two parts of the clutch. That is what you shim. Close up that air gap a bit and it should continue to work for years to come. Or, you can replace the clutch (new are big $, but you can usually find one at the junkyard for cheap).

http://www.autoacforum.com/messageview.cfm?catid=2.&threadid=14277

You'll note in that link that they talk about a shim washer on the clutch. Same idea (better actually) but installing it there means you have to get the compressor clutch off of the compressor. Getting that nut to break loose can be a problem, which is why I use the wire on the fingers.

Though I'm open to suggestions that doesn't account for why the clutch engages every time it is jumped. Also, after it has gone out it will not come back on even after sitting half a day unless it is jumped. Also, When jumped I have run it for about 30 minutes at a time with no issues so far. Just seems odd...

 

[RonD]

From a '97 ranger A/C diagram there are two pressure switches, three if you count the WOT(wide open throttle) cutoff switch.

The A/C clutch cycling switch, open if below 25psi or above 45psi, so clutch engaged with 25-45psi

Then the A/C Pressure cutoff switch, it opens at about 460psi, won't close again until pressure is below 300psi

Have you checked the pressure immediately after compressor quits working, you could have a partial blockage in the system causing pressure to build up.

 

[PanamaExpat]

Next time it does it throw the slider all the way over to defrost and see if it engages the compressor. If it does look for bad connection at the dash control module or possibly the little switch that engages by pushing in and out on the fan speed control has a bad solder joint or is in need of cleaning or replacement. You could just have a dirty connection.

If you look at the wiring diagram you will see that the defrost position bypasses the AC switch on the fan speed control.

Wiring diagrams here for free: http://search.ebscohost.com/ Username: tech Password: tech then select the ARRC link.

 

[killj0y]

From a '97 ranger A/C diagram there are two pressure switches, three if you count the WOT(wide open throttle) cutoff switch.

The A/C clutch cycling switch, open if below 25psi or above 45psi, so clutch engaged with 25-45psi

Then the A/C Pressure cutoff switch, it opens at about 460psi, won't close again until pressure is below 300psi

Have you checked the pressure immediately after compressor quits working, you could have a partial blockage in the system causing pressure to build up.

True but any way to test the switches since I don't have cash to buy the other 2 just now. I'll check with the gauges immediately after failure. I have run it jumped and runs great. It isn't ideal of course but I know theres a proper charge in there. Finals are this week so it will ave to wait till sunday

Next time it does it throw the slider all the way over to defrost and see if it engages the compressor. If it does look for bad connection at the dash control module or possibly the little switch that engages by pushing in and out on the fan speed control has a bad solder joint or is in need of cleaning or replacement. You could just have a dirty connection.

If you look at the wiring diagram you will see that the defrost position bypasses the AC switch on the fan speed control.

Wiring diagrams here for free: http://search.ebscohost.com/ Username: tech Password: tech then select the ARRC link.

I have the wiring diagrams off alldata, but thanks! Also, ill try the inside switch like you suggested. I have fidgeted with it and no go but i didnt try defrost. only messed with the level and temp. I know The temp knob only reads cold at the highest level (as in AAAAll the way to the left bottomed out) any other setting is heat. I figured it was the module but not sure wy it would fail now or if it is even related.

 

[kimcrwbr1]

Have you checked the delta T in the cab measure the temp of the air coming out the vents to the temp going into the coil you should have around 20 degrees difference. If you are tripping the low pressure limit switch ony three things it can be.
1- low on charge your not getting liquid to the expansion device
2- plugged or restriction in the expansion device (piston) or plugged filter drier?
3- bad connection/connector or bad limit switch
If you are not checking superheat and subcool when you hook up the guages your spinning your wheels remember ever time you connect your guages your taking refrigerant out of the system approximately 1 ounce of liquid. Try and achieve 20 degrees of delta and wait for at least five minutes running before takeing your readings every time you adjust the charge. The danger of bypassing the low pressure cut out is running the compressor without oil so make real sure it is working correct or you will be replacing the compressor in short order.

 

[kimcrwbr1]

I was just thinking do you have the WOT cutout relay in your system maybe something to look at also?

 

[killj0y]

Well all things to check out thanks. Ran it this evening jumped and it ran fine the only other hiccup was for a brief moment I noticed it wasn't blowing through the vents or anywhere else. I could hear the blower going and it was really cold but it was like the blend door was shut but allowing barely any air through even though the blower was responding to the change in speed. Hmm got a new switch coming in tomorrow just to rule that out. Just wish I had time to better diagnose. I just got home and have to get to work with school since my last final is tomorrow. Friday evening I'll have a little time to double check everything. If I'm lucky it's just a bad switch :thumbup: that would be nice

 

[killj0y]

I was just thinking do you have the WOT cutout relay in your system maybe something to look at also?

I believe I do since at wot it has always cut out

 

[killj0y]

Just an update, haven't had time to get anything done to the truck lately, so the ac is so jumped and has been running great, not sure if I mentioned this other symptom but after about 30 minutes if driving or so it will be blowing but nothing coming out the vents. Like something is blocking it. It's still cold as hell just barely there even though I can hear the blower going strong, strange. If the compressor hadn't eaten itself up and hasn't stopped blowing cold I doubt it's a leak. Could it be the orifice tube? I hope not because that's such a pain and I don't have the money to spare to rebuild it all. I'd do the work sure but I'm sure the parts would be 100-200 bucks. No time or money, that sucks. Hmm, I'll def try to make time this weekend though to at least run it and monitor it for 30 minutes to an hour to get a good pressure reading. Like I had said the initial reading was fine. I'll probably pick up a few cans of refrigerant since I think a few of the other vehicles need a top off.

 

[Tedybear]

If you jump the system, if the compressor is running all the time without cycling correctly? You'll freeze the evap into a block of ICE. That will cut off the air flow and you won't get it back until the ice melts.

The system is designed to turn the compressor on and off in almost a rhythmic cycle. This is to ensure NOT turning the evap core into a block of ice, and also for safety. If the compressor is always 'on' and not cycling? You'll get some dangerous pressures and quick!! You can verify that if you can find someone with a set of AC gauges..

Another question would be, is this system on R12, or R134a...and if the latter? Was it converted or always like that. (I've been out of the automotive ac game for many years and do not know when they outlawed R12) There is something called the "Black Death" where the new freon can actually destroy the material in the receiver/dryer and spread black garbage all over the system and it won't run correctly. Not saying this is the case, but it was a huge problem years ago.

S-

 

[killj0y]

If you jump the system, if the compressor is running all the time without cycling correctly? You'll freeze the evap into a block of ICE. That will cut off the air flow and you won't get it back until the ice melts.

The system is designed to turn the compressor on and off in almost a rhythmic cycle. This is to ensure NOT turning the evap core into a block of ice, and also for safety. If the compressor is always 'on' and not cycling? You'll get some dangerous pressures and quick!! You can verify that if you can find someone with a set of AC gauges..

Another question would be, is this system on R12, or R134a...and if the latter? Was it converted or always like that. (I've been out of the automotive ac game for many years and do not know when they outlawed R12) There is something called the "Black Death" where the new freon can actually destroy the material in the receiver/dryer and spread black garbage all over the system and it won't run correctly. Not saying this is the case, but it was a huge problem years ago.

S-

Well it actually does cycle on and off I've heard it and verified while parked. I have gauges like I said initial reading was fine and I haven't had time to check it after letting it run a bit so I'll do that this weekend. And it's currently and always has been R134a. In the mornings I have noticed a little mist from the vents, but it had been humid as of late so I chalked it up to that since previous vehicles I've owned have done that on occasion. It blows cold as hell still so the charge coincides with it still cooling. Dunno what it could be. I do know that when I swap out the sensor for a new one it works for a few minutes then cuts out. Removing and reinstalling does nothing though. Neither does letting it sit with the sensor attached. This is the third sensor so far. I didn't try another new one since it seems it's something else. Like I said I'll recheck the gauges and report back this weekend I suppose. If need be I got some mechanic friends who do ac and they've taught me everything I know so I'll check with them if I can't figure it out. I hate asking for favors that's all.

 

[snake]

You said the gauge numbers "check out" but what are they? If those vents are defaulting to defrost going uphill but revert back to normal on downhill you likely have a vacuum leak in the vent system, a completely different problem. If the air isn't going anywhere suspect a freeze up as mentioned up top on another post. I, too, doubt you got three bad low pressure switches. Rev the engine to about 1500 rpm and see what you have numbers-wise. Might be a bad clutch fan not cooling the rad and causing the high pressure switch to shut it down. If those high side numbers are high keep the condenser cold with a water hose and see if the numbers drop significantly- if they do it isn't being cooled properly. Oh- and if you jump the low pressure switch it still should cycle because of the thermostat- providing it is getting cool enough to trip off.

 

[Tedybear]

I'm glad you mentioned it's cycling. Without seeing it in front of me? Trust me, I've seen A/C bypassed and it really makes a mess if not done correctly and the other supporting sensors/switches are not 100%. Let us know the gauge readings--It's been a while, but I still get interested <G>

S-