R4 Scroll Compressor Experience

[studigggs]

I know by writing this I will have doomed my compressor to fail, but here goes. I've been through five R4 compressors in the last 6 years (tried New Delco, New 4Seasons, Reman 4Seasons) and all of them failed in a similar manner... upon restart after a heat soak in the desert summer (105+ deg) they would no longer put out any pressure and oil could be seen leaking from the outer case. I finally gave up and tried the UAC scroll compressor in R4 format and must say I've been pleasantly surprised. Had it in all summer and have really beat the hell out of it (by that, I mean treating it like a normal compressor and not turning it off 60 seconds before reaching my dest and waiting 60s to turn it on after heat soak like I did with the last three R4s). Sure, it does not cool as well as the piston R4, but I was expecting that. I would compare the cooling capability to any of my more modern cars though. The piston R4 was really in a class of its own as far as cooling capability.

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[PlayingWithTBI]

Is that in your 90 (from your signature)? Did you have the high pressure shut off switch wired in series with the low side switch?

BTW I can't get your link to work...

 

[studigggs]

Yes, installed in the '90. No, I haven't modified the factory wiring. fixed link ( I Think)

 

[PlayingWithTBI]

A good way to tell if you have a high pressure shut off switch is; if you have a "max air" or "recirc" button then you do. Otherwise, the OE 1-wire switch on the back of the R4 compressor activates the fresh air door so, when you have A/C on, fan on med or high, and your temp control is on its lowest setting, and pressure goes over ~200PSI then, after 30 seconds, your air door will open for better cooling.

This all means that you don't have a high pressure shut off so, in the heat when you start your truck with the A/C on your pressures will spike and blow seals or, in my case, it blew the high pressure switch out of the compressor (sounded like a shotgun going off). With the 2-wire HP switch wired in series with the LP switch, if pressure goes over 430PSI it'll shut off the compressor until it drops to 200PSI protecting the system. Also, your system was an R12 system which uses a different orifice tube. You should use a tube from a later model truck (black instead of white). HTH

 

[Schurkey]

The R4 compressor was known as a high-failure unit especially in it's early years. The A6 was still "king", but weighed a ton and took a lot of power to turn.

R4s got better as time went by.

If you had multiple failures with an R4, something else is wrong. First Guess: particles clogging the orifice tube, resulting in high high-side pressure and low low-side pressure. Eventually the compressor spills it's guts.

 

[PlayingWithTBI]

^^^ X2 - I was assuming (I know assume = ass out of u & me) the system was flushed and evacuated each time, as it should be whenever there's a failure and it's opened up.

 

[L31MaxExpress]

The R4 compressor was known as a high-failure unit especially in it's early years. The A6 was still "king", but weighed a ton and took a lot of power to turn.

R4s got better as time went by.

If you had multiple failures with an R4, something else is wrong. First Guess: particles clogging the orifice tube, resulting in high high-side pressure and low low-side pressure. Eventually the compressor spills it's guts.

Agreed on the A6. Heck it even has its own internal oil pump. It is the highest displacement piston GM compressor. Something like 12 cubic inches per revolution. Even with a smallish old style condensor it cooled my old G20 van well after changing out the fan to a factory big block 7 blade with a heavy duty clutch. It would hold about 42°F from both evaporators with R134a. Fortunately it had a WOT shut-off switch or else my 305 probably would not have gotten out of its own way with the a/c on.

That being said I have converted a couple of these trucks to Vortec accessories and used the valeo or sanden style replacement vortec compressors. They are a smooth operating 6 cylinder compressor with enough capacity to get the vent temps on both front and rear evaporators in my Express van into the 30s on a 105°F day in Texas humidity. The Vortec setup is a much nicer setup from the brackets on. I have reused the TBI water pump and crank and water pump pulleys by spacing the accessories out with 1/4" thick 3/8" washers. The TBI power steering pump swaps over as well. Swapping out the brackets also allows a AD244 alternator to bolt directly on. I have a few local yards that sell the brackets dirt cheap. They can even come off a 4.3. Anyone interested in doing this just be sure to grab the a/c manifold hose as well as the metal bracket with the engine removal hook on the driverside front of the engine as it serves as both a spacer and a p/s pump mounting point.

 

[studigggs]

The R4 compressor was known as a high-failure unit especially in it's early years. The A6 was still "king", but weighed a ton and took a lot of power to turn.

R4s got better as time went by.

If you had multiple failures with an R4, something else is wrong. First Guess: particles clogging the orifice tube, resulting in high high-side pressure and low low-side pressure. Eventually the compressor spills it's guts.

Possible I'm doing something wrong. I dont have filtered shop air for flowing through after I flush. On the last 4 I replaced the condenser in addition to O-tube, drier and compressor. Used the GM oil (8 oz). Again, all of my repairs have run flawlessly for months until they heat soak. On the last one I installed a new Delco unt in Feb, and I ran it from Feb - June nonstop thinking I could "break it in" before the summer hit. When June (and the heat) came around, I was shutting the AC down 30s before I reached my destination, and not turning it on after heat soak until the truck was moving @ 30mph the road. I got cocky thinking I'd finally licked it, and sure enough, two days after I started treating it like a normal AC, it stopped blowing cold and I found fluorescent dyed oil leaking from the outer case and down the AC bracket. That's when I went to this UAC unit.

The UAC has been in for 2 months during the hottest part of the year (105+ for the last month) and I have not babied it at all. pressures are just right per the R134 chart. Time will tell, I guess (it does say Made in China). I'll update if it goes kablooey again.

BTW, Shurkey, thanks for the advice on the MT2500 a few months back. I love that thing and just bought a Vantage to go with it.

 

[studigggs]

A good way to tell if you have a high pressure shut off switch is; if you have a "max air" or "recirc" button then you do. Otherwise, the OE 1-wire switch on the back of the R4 compressor activates the fresh air door so, when you have A/C on, fan on med or high, and your temp control is on its lowest setting, and pressure goes over ~200PSI then, after 30 seconds, your air door will open for better cooling.

This all means that you don't have a high pressure shut off so, in the heat when you start your truck with the A/C on your pressures will spike and blow seals or, in my case, it blew the high pressure switch out of the compressor (sounded like a shotgun going off). With the 2-wire HP switch wired in series with the LP switch, if pressure goes over 430PSI it'll shut off the compressor until it drops to 200PSI protecting the system. Also, your system was an R12 system which uses a different orifice tube. You should use a tube from a later model truck (black instead of white). HTH

My high pressure switch only controls the recirc door. I did think about wiring it to the low pressure switch, but I really like the 'automatic' fresh/recirc door operation. It brings back memories of driving this truck in High School in southern Louisiana. I was always amazed how the damn truck just knew when I was getting too hot and would blast me with super cooled air the next second. It was witchcraft back then. But yes, the failure you are describing (and you live in a similar climate) appears to be what I'm dealing with.

 

[PlayingWithTBI]

High pressure shut off 1st, then you just ground the OE wire to the T-Stat and it'll work just fine.