So I was sitting in traffic today, and heard a loud hissing noise. Apparently the pressure relief valve on the high pressure refrigerant hose was the source of the noise. There was a nice yellowish splattering of oil below it on the compressor, and a puddle of oil on the road shield. I replaced this hose a couple of years ago with an aftermarket part. I figured the one from the factory fails so frequently, that I might as well try someone else's hose.

Funny thing, is that even with what I assume is a zero charge on the system, the compressor clutch responds to the switch. I would expect with no pressure in the system, it would keep the clutch disengaged. This makes me wonder if my dual pressure switch failed closed, and this caused the pressure to run too high and blow the valve on the flex line. I'll check the pressure tomorrow, and also continuity on the switch.

Is the pressure relief valve on the hose a one time valve that blows, and then you replace the hose - or does it close when the pressure drops below 540psi?

Has anyone else experienced this?

Q451990 wrote: ↑

Fri Jun 18, 2021 11:31 pm

Funny thing, is that even with what I assume is a zero charge on the system, the compressor clutch responds to the switch. I would expect with no pressure in the system, it would keep the clutch disengaged. This makes me wonder if my dual pressure switch failed closed, and this caused the pressure to run too high and blow the valve on the flex line. I'll check the pressure tomorrow, and also continuity on the switch.

Is the pressure relief valve on the hose a one time valve that blows, and then you replace the hose - or does it close when the pressure drops below 540psi?

Sounds like that's exactly what happened. The triple pressure switch works indirectly, when it opens it prevents the ECM from seeing the compressor request from the HVAC panel, thus causing the ECM to turn off the A/C relay. If it fails closed then the ECM will turn the relay on regardless of system pressure, over or under. The blowoff valves are spring-loaded and are supposed to reset, but don't always seat back where they belong. Add a small amount of refrigerant and check for leaks after you replace the triple switch.

So I got a chance to check it today. There is a little bit of refrigerant left in the system. With the compressor off and everything equalized I get about 80 PSI on both sides. With the compressor on, it reads 7 PSI on the low side and 71 PSI on the high side. I didn't run it this way for long. The switch is a little hard to get to for testing with a meter, but if I unplugged the switch, the compressor turns off, then turns back on as soon as the switch is reconnected. So it seems like the switch is stuck. The service manual is says the pressure switch should be on while pressure is "Increasing to 23-31 PSI" on the low side, and off while "Decreasing to 23-28 PSI" - on the High side it says it should be off while "Increasing to 384-412 PSI" and on while "Decreasing to 199-256 PSI"

I guess either way, my pressures are way too low for the compressor to be running, indicating a stuck pressure switch.

Another concern is how do I know how much refrigerant oil to put back in the system? The manual says to add 30ML for a "large leak" - but this was a heck of a leak, spewing the contents of the system under pressure. Any thoughts on that?

Also, would you replace the high side line for good measure - or since it's held some pressure, assume that the relief valve is seated properly?

If it's holding pressure then the valve re-seated, I wouldn't worry about that. They do tend to lose a lot of PAG when they blow off, I think I'd add a bit more than the 30mL but not a lot more, 40mL would be my best guesstimate. Slightly overfilled doesn't really hurt anything, it just slightly reduces cooling capacity.

I have parts on the way. I guess I know what I'll be doing next weekend.

I swapped out the drier and pressure switch, added oil, and was able to pull a nice vacuum overnight showing a little below 30inHG. I isolated the system, and it held for about an hour. I should have quit while I was ahead and charged the system, but I put the vacuum pump back on to leave it for a few more hours. When I got home, the pump had shut off (thermal cutout?) and my vacuum was only at about 10inHG. Now the pump won't pull even just the gauges with the system isolated below about 28inHG. I'm just hoping it didn't suck vacuum pump oil into my system!

All of this led to the ultimate "f-it" moment where I ordered my own JB Industries vacuum pump and a micron meter from Zoro last night. That pump should outlast me, hopefully my sons can get some use out of it too. I'm done with these AutoZone loaner pumps!

I finally received the new vacuum pump and micron gauge last week while we were out of town. Hooked everything up tonight, and got it down to 270 microns in about 10 minutes, and held it nicely with the pump off for 10 minutes. I charged the system and confirmed that the pressure switch is working. Let's hope all of this holds up for a while. I'm ready to drive with the windows up again!

So my truck must have a thing for that new vacuum pump.

Today I noticed that the air wasn't so cold coming out of the vents.

I decided it was time to get out a can of engine cleaner and clean up the big oily mess from last time. Here's everything cleaned up:

And after about a 5 minute drive. It looks like the pressure relief valve on the high side hose didn't seal back up properly:


So it either failed a day or so later, or seals under a vacuum, but not under pressure - because my new super duper digital micron gauge had everything holding an awesome vacuum on Monday night. Hey, at least this leak was easy to find!

Yep, they usually seal back up, but not always. Internally most of them are a flare seat with a spring, so it only takes microscopic crud to make them leak. But at least it's not anything nasty like a cracked evap!

It probably doesn't help that it's an aftermarket hose. With the factory one being such a common failure point I figured if I'm buying crappy either way, I'd rather pay less for it.

Q451990 wrote: ↑

Sat Jul 17, 2021 10:49 am

I figured if I'm buying crappy either way, I'd rather pay less for it.

So I swapped in a new hose yesterday, and all is well for the moment. Maybe this fix will last more than a week.

I'm back in the spirit of "how many times must one fix something before it's fixed" - and self humiliation. Air conditioner performance has been once again deteriorating over the last couple of days. It appears that my high pressure event damaged a seal on the compressor. I'm living proof that holding a great vacuum doesn't mean a leak free system. Here's a nice video of my compressor blowing bubbles.



The only thing I don't understand is why I'm not seeing UV dye here? An electronic leak sniffer goes bonkers in this area, so I'm convinced there's an actual leak.

At this point, I'm wondering if anyone has had success resealing a compressor with a reseal kit and new shaft seal?

If not, I'm probably firmly in RockAuto China compressor land. Does anyone have a favorite brand of aftermarket Chinese compressors? I can't justify a $900 factory compressor at this point.

Or tannerite - that could be the best option.

So I ordered seals and resealed the compressor. For anyone looking, AutoZone had two parts listed for the shaft seal. The Santech MT2060 and MT2250. Not knowing which one I needed, I ordered both, along with the MT2130 Compressor Gasket Kit. The 2250 looked the most like what was in the compressor, and it's much cheaper at $9.59 vs. $28.99 for the other one. Unfortunately I messed up the cheaper one putting it on. I believe I need some sort of seal installation tool that slides over the splines of the shaft to keep from damaging the inner surface of the seal. So both seals fit, get a tool. Using enough oil and being really careful I was able to get the second one on without damaging it (at least to the point that for now it's holding pressure).

The middle o-ring was the source of my leak. I used a loaner tool from Advance Auto to remove the clutch. Of course the kit didn't come with the correct size bolts to fit in the three threaded holes in the front of the clutch, so I spent more time that I care to admit digging around in my bucket-o-random bolts finding ones that would work. A puller was necessary to remove the pulley.

So we'll see if this fix finally fixes it. If it makes it to September, I'll probably vacuum it down again and change the receiver dryer, as I didn't have one today and gave my compressor reseal about a 5% chance of actually working. If this doesn't work, I'm going to throw all Rock Auto parts at it (condenser, drier, evaporator, compressor) and hope for the best. At least I'll know I have the correct amount of oil in it again.