A/C stopped working, excessive pressure on low pressure side

[gmcman]

Letting the engine idle for about 30 min, ambient temp is 78 deg, measure in front of the condenser.

I have at idle, 28 PSI / 175 PSI, if I rev the motor slightly the high will climb near 200 PSI then cycle off.

If I hold the RPM's at 2000 for a few min, cycling the compressor about 10 to 15 times it will stop working.

Light mist of water on compressor will turn it on again.


Edited to add, at idle the compressor stays on, only cycles if I raise the RPM. Doesn't seem to build pressure when idling, if so it's very very slow.

 

[Texan]

I think that you are slightly low (half of a can) on Freon.

 

[c good]

134 charge is in the ballpark while compressor is running. Slightly low but not enough to keep turning off the compressor.

Did you read my post about weak field coil?

Don't waste any more of your time. It needs the shim removed first, if this doesn't work then you need a new clutch/coil assembly or a new compressor if you can't find the parts.

 

[meerschm]

agree the compressor clutch coil seems a little weak, and R134a could be a little low.

I got my AC clutch repair kit from airpartsinc, on e-bay.

process was to contact via e-mail, and they posted a kit for sale on e-bay, very smooth,

and the replacement was possible, but a little tricky to get the snap rings back where they go.

they seemed surprised I would want to change this out with the compressor on the truck, and not on the bench.

looking back, I pulled the radiator fan and clutch for access, then it was possible to get to the snap rings that hold the bearing/pulley, and the coil. the clutch plate is held on over the spacers (skinny washers) by a nut.

 

[meerschm]

a few photos to help.


http://gmtnation.com/forums/uploads/gallery/album_36/med_gallery_8039_36_318567.jpg

http://gmtnation.com/forums/uploads/gallery/album_36/sml_gallery_8039_36_126127.jpg

http://gmtnation.com/forums/uploads/gallery/album_36/med_gallery_8039_36_679249.jpg

and

http://gmtnation.com/forums/uploads/gallery/album_36/gallery_8039_36_18992.jpg


http://gmtnation.com/forums/uploads/gallery/album_36/gallery_8039_36_161466.jpg

last one shows the coil on the compressor. it is held on with an o ring, which is the hardest one to get, since it is buried within the opening. (fits in the slot furthest from the shaft threads in previous photo.)

 

[Mooseman]

I tried to find the parts at airpartsinc, can't seem to find the kit. Do you have a link?

 

[meerschm]

http://myworld.ebay.com/airpartsinc

login with your ebay account, and send a message to airpartsinc,

tell them what you are looking for, and they will provide a price and make a lising for you to use to buy it now.

just let them know model year and style truck (and if it is an ext with rear ac, it might make a difference, not sure), part number from the compressor is probably optional.

I get the impression they have lots of stuff, but post what you need, rather than maintain a catalog online. that way they only pay listing fees for what you want to buy.

first of april 2013, I got a

Chevy Trailblazer Sanden 3450 Rebuilt A/C Compressor Clutch Assembly
( 161000018234 ) for around $70.

 

[meerschm]

http://gmtnation.com/forums/topic/7652-ac-clutch-replacement/

found the info I posted before.

you can also call airpartsinc at

800-223-7167

 

[Tiggerr]

Someone should sticky the info for them. Can't ever have too many parts sources. Especially AC parts

 

[gmcman]

So I had time to get dirty today, I have a spare A/C electric coil for the clutch just in case so I figured I would try to get in there and see if the pulley would come off without a puller since I really didn't feel like pulling the fan and shroud for clearance. The clutch came off easy but no go on the pulley without a puller. So I figured even though I have .016-.017" air gap on the clutch, it wouldn't hurt to see if there's a shim in there I could remove....and there was. The friction area of the clutch wasn't badly grooved but there was grooves so my air gap measurement between the outer portion of the clutch didn't have much bearing on the actual gap in the grooves.

So I removed the shim and reassembled, I still have a gap at the outer edge but not alot, maybe .003 ish....about the gap of a piece of paper. There was no rubbing, clutch spun freely, I started it up and with the ambient at 81 deg my high side was about 140-145 so I added some 134A. When the video uploads I will post it but I'm holding about 200-215 PSI on the high side but will cycle if I rev the engine to about 2500.

Before I couldn't get the compressor to cycle 10 times before it shut down, now it's been running for over 45 min, no issues, I raised the RPM to 2500 for a few minutes and still no issues. Chances are I may not be out of the woods yet but after a few driving cycles I will report back.

 

[c good]

What is your low side pressure and high side pressure at the same rpm? It's good to have both numbers to help troubleshoot.

 

[gmcman]

What is your low side pressure and high side pressure at the same rpm? It's good to have both numbers to help troubleshoot.

I tried to get a vid uploaded but I will try again later.

When the ac wasn't cycling, I was getting roughly 40 to 45 on the low and about 215 on the high side, idling, 81 deg ambient.

 

[c good]

So...with compressor running, you're getting 40-45 Low, and 215 on high side. You're over filled.

 

[gmcman]

This is before I added a little freon. Ambient is 81 deg, recirc is off. RPM 2000.

I'll fix the crop later but the low drops down to about 22 -23.

Edited to add: Fixed video crop.

https://www.youtube.com/watch?v=eiuUsPn2_8o&feature=youtu.be

 

[ek02]

Your gauge readings look exactly like mine yesterday when it was really hot out and my A/C did not feel as cold as it used to be. I added about 9-10 ounces of 134A and the pressures came up to 30-32 PSI on the low and 250 on the high side @ 2000 PM with the blower on high, and the clutch stopped short cycling. If the suction hose is frosty cold all the way back to the compressor, and the accumulator is not iced over, the system is full and working properly. That is how I have always judged if a system is low without discharging the system and refilling with the correct amount, which is the right way to do it if you have the equipment. Ambient temperature, the amount of air flowing over the condenser, and the blower motor speed all affect the pressures. I would add Freon until the metal on the suction hose is cold where it bends down toward the compressor, then look at your gauges. As long as the high side is not over 250-275 @2000 rpm on a warm day you should be fine. The cooling fan has to up to par or the high side can go way up. Temperature and pressure are directly related in A/C work. 30 PSI on the low side is about 35 degrees in the evaporator. Temperature is on the gauges in red numbers.

 

[gmcman]

I added roughly the same amount, I will recheck pressures tonight since it will be near 90. Now that I can upload vids again, I will give a current video but my high is around 215 and is cooling pretty good.

I drove it a few more times, still no problems. Fingers crossed.

 

[gmcman]

I didn't bother with a video since the readings were steady. You can cut the air with a knife here right now, It's like a swamp, but this is the air entering the condenser and the current readings. Engine was at steady 2000 RPM. Was getting 52 deg from the vents without recirculation.

 

[Mooseman]

Without recirc, you're just sucking in hot engine air. With recirc, it should be right. Those pressures look good.

 

[gmcman]

Without recirc, you're just sucking in hot engine air. With recirc, it should be right. Those pressures look good.

Ok...thanks. I will let it go for the week and report back. Hopefully the shim was the culprit for the shutting down of the compressor.