MarkinIdaho

'02 GMC Yukon w/ 255k miles, 75 degree ambient temp
Good low side pressure. 30-35 max low side. High side only reaches 130 max psi before cycling off. Both sides vary 10 or so. 60 psi off/resting. cold tubes, inadequate cold air. Charged to peak low pressure, 40 psi. Could seals fail at 130 but work below? Could bad cut-off switch be stopping full pressure? Leaks slowly when used on hot days but maintains pressure if not used. UV checked. no visible leaks

tech2

rev the engine up to 2500 rpm and hold it there...do you get cold air?

josh336

sounds like you are a little low on freon. Like tech2 said, turn ac on full blast (front and back) hold rpm 2000-2500. I may be mistaken, but, the ac clutch should come on and stay on in these conditions. If its still going on and off you may need to add a little. Good luck

MarkinIdaho

It has been a cool week. Finally got 75-80 degrees. I tried 2500 RPM. Got some cooling but not cold.Low pressure pipes cold but no cold blast in cabin. Pressure was 100 high, 30 low. Added some 134. High pressure never went above 100. Wasn't watching low at first. Then I notice low was at 100. Then, checked for cold in cabin and came back to 30 psi on high and low.sides. Shut down and let it settle. 30 psi on high and low. It normally rests at 65 high and low with a charge at 65 to 70 ambient. With the engine noise from running at 2500, I have no idea where the freon went. No signs of a leak anywhere.
I vented it at low pressure side and pulled the orifice. It is clean. Only took 10 seconds to vent so it had lost the freon charge.
I closed it without the orifice and pressurized with just freon can pressure. Checked for leaks. I did not run the AC for fear of dry pump. I pressurized the system with air to 100 psi. It has held for 2 days. 100 psi at 70.degrees ambient 120psi at 85 degrees?. 100 psi again this morning.
My thoughts. Bad shaft seal at pump that does not hold high pressure but holds 100 or below ?? It was previously peaking at 130 psi. No obvious oil or UV at back of clutch??
Could the system be low on oil from previous top offs without oil? Over the past few years, I only added a charge with oil once out of 4 cans. Venting blows oil but not much.
Option A... Flush system, new orifice, evacuate, add oil and recharge with 2.7 lbs of R134 so I know I have a proper charge
OR Bite the bullet and
Option B... R&R pump, orifice and accumulator, evacuate and recharge ?
At 255,000 miles, would the pump be just weak but not failed?
If low oil, is pump toasted even with clean orifice?
When is was cycling, it would engage for 5 seconds then off for 10 or 15 seconds but never pressurized above 130 psi.

josh336

dang, i hate you drained the system already! Before i wrote off the compressor, id try a few more things. First you need the orifice tube back in the system to get accurate pressure readings. re install that. next id hook up a vacuum pump to the gauges and pull a vacuum for 20 minutes or so. Air may tell you its not leaking, but youve just added moisture to the system ( no bueno ). if it holds vacuum, which it probably will because of your pressure test results. I would then recharge it and run it again, this time id jump the pressure switch with a paper clip. this will tell the compressor that everything is good, and allow it to stay on and give you accurate pressure numbers. right now with the short on off cycles, you arent getting accurate readings. may be a simple pressure switch. find out why it short cycles and you will have it wooped. usually short cycles are caused by low freon, or bad pressure switch. you can jump the pressure switch or run 12v jumper to the compressor clutch to keep it on long enough to get a accurate reading on your gauges.
if compressor was toast you would of seen evidence all over the orifice tube.

MarkinIdaho

The forum lost my reply. Try again.

I did not intend to drain the system. When it went from 100 psi to 30 psi, both high and low, I figured it had dumped the 24+ oz I just put in.
The orifice has a tiny amount of debris, some black fiber and 1/16th x 1/8th clump on one screen.
I'm thinking. New pressure switch and orifice. Vacuum for 30 minutes, see if it hold vacuum, recharge with freon and oil.
Will the vacuum clear the residual oil or should I use air and maybe flush fluid to blow it out before vacuum?
I don't want to charge with too much oil. It needs 11 oz of oil plus 42 oz of freon.

Try $60 test versus $350 replace it all.

I flushed it, I got very little out with the flush, maybe 2 ounces of oil. Installed the orifice, put the vacuum on for 30 minutes and then added an 11 oz oil charge and full charge of freon. Never could get high side above 100 psi. Cycles every 9 seconds. Swapped the pressure switch, no change. Getting some cooling but not great. Cool air but not cold air. We'll see when it heats up. No holding my breath.

tech2

that is a lot of oil to add to a system. total system oil capacity is 11 oz...your flushed 2 out...maybe you lost 2-3 if the system suddenly depressurized...the rest of that total system capacity is trapped in the system. each major componet will hold oil that will not drain unless you remove the part and poured it out.
short cycling is a symptom of low refriderant but maybe search oil slugging what that can cause. oil slugging will definitely reduce system performance.