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Retrofit question on GM truck

Hardrock on Sun August 26, 2012 2:17 AM User is offline

Year: 1993
Make: Chevrolet
Model: Silverado
Engine Size: 6.5
Country of Origin: United States

First off, I'd like to say thanks to the help of this forum, my '98 Tahoe is still providing ICE COLD air over a year later.

This time, I'd like to get some input on upgrading my 1993 K2500 pickup to 134a. The truck is completely apart and undergoing restoration. As you know, this was the last year GM trucks left the factory with an R-12 system. I have access to a 1994 truck with working A/C that came with an OEM 134a system. My plans are to remove, flush, inspect, and swap the entire 134a system from this 1994 truck into my '93 as it goes back together. Evaporator, condenser, manifold, hard lines, etc. Anything not passing inspection will be replaced with new.

Even though both systems are virtually identical, save for refrigerant, there is a minor difference in that my '93 has no HP switch in the compressor, nor does it have the LP cut off switch at the condenser. My '93 isn't wired for those, and never had them. (Both trucks came OEM with R4 compressors.)

Can I run this new 134a system without the HP and LP cut off switches just like the '93 did when it was built??
(I really don't want to patch into the factory wiring if I don't have to)

Since R4 compressors are somewhat trouble prone, and the '94 I have access to has approx 100,000 mi. on the original compressor, I'd like to replace it with a Seltec HD6 type compressor if possible. I've compared the R4 mounting with an HD6 from mid '90's full size vans, and it looks do-able. Is this possible? What problems might I encounter? Any idea what this hybrid system might require for total oil capacity? Thanks, any help would be appreceiated.

AutoCool on Sun August 26, 2012 4:26 PM User is offline

Isn't there a low pressure sensor on the accumulator? Seems odd that there would be no switch at all. Maybe someone previously removed it, no fitting on the accumulator?

iceman2555 on Sun August 26, 2012 6:07 PM User is offlineView users profile

This vehicle did not use a HPCO switch, but a PRV located in the compressor. Also the LPCO is located on the accumulator. It is possible to operate this vehicle as designed with 134a. Look very closely at your condenser. Some of these late model vehicles were being equipped for the change to 134a. Many had the newer design HE condenser factory installed. If so, this is a no brainier. Recover refrigerant, flush and clean the system, add correct lubricant (PAG 150) and recharge to a complete fill of 134a. If the condenser is newer design unit, it will handle the higher operational pressures of 134a.
A suggestion, if the condenser is not the HE unit, simply replace the factory unit with a updated condenser, typically supplied as a 6mm pic. This one step can remove most all of the problems typically associated with retro fitting. If the updated condenser is installed, there is no need to undercharge the system....go with a full 134a to 12 recharge. Insure the fan clutch is operating correctly...and other engine cooling systems are operating correctly and you should have a viable very operating system. The statement that the R4 is a trouble prone compressor lacks validity. The longevity of this unit and it's operational mileage do not substantiate this statement. If the system is serviced properly, recharged correctly, lubricated properly and the engine cooling system is functioning, the compressor should over many years of service. The major cause of R4 problems is the lack of lubricant flow to the compressor. This is not a fault of the compressor but at fault of the installer that fails to properly service the system. The major cause of compressor failures, over 97% is directly related to lack of lubricant flow...this is not a problem with the faults a service procedure. Recharging is a most critical aspect of a repair and often this is the area of most concern. Once your system is assembled...have it professional not attempt to charge by cans and pressures....this is a major step toward reduced compressor longevity.
The Sanden replacement for the HT 6 is a good unit...but the change over requires many changes (additional parts) and extra cash. Once more the installation of this compressor will not relieve the problem of longevity, if the system is not serviced properly. Once more the life blood of the system is the flow of lubricant....the major controlling factor for this migration is the amount of refrigerant recharge. Short charge this system by 3-4 oz and the compressor will fail....not doubt.
Good luck

The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

Hardrock on Mon August 27, 2012 3:26 PM User is offline

Thanks for the reply Iceman. Looking these two systems over again, I believe the '94 has a LPCO switch in the compressor, and a HPCO switch at the condenser. (At least according to the parts book.) My '93 only has the clutch cycle switch on the accumulator. Nothing in the wiring has been monkeyed with. The compressor isn't even machined for a switch. Checked a few other '93's, they're exactly the same as mine.
What I could do, is patch in a LPCO pigtail right at the clutch plug-in, if that might safeguard against compressor failure later on.
I'll have to make sure the '94 switch is in fact a LPCO and not a HPCO, though.
I'll for sure go with a new HE condenser, as the '94's condenser may not be easy to get adequately flushed.
I dont know if the '94 evaporator is HE or if just the fittings are different from '93, but they have different part numbers. I did notice the donor truck has a set of replacement Goodyear hoses that look clean and dry, so that's a plus.

My biggest reason for wanting to upgrade from the R4 style compressor is because all the GM vehicles I've ever owned that had one, either never worked, or if they did, didn't last long. I agree, most likely failure was lack of maintainence, but most everyone I've talked to seems to believe the R4 takes a lot of power to operate, and the H6, HD6 are more efficient and create less parasitic drag. (it's all about fuel mileage, nowadays! LOL!)
I'm pretty good at fabricating, so if I can get a HD6 clocked right so my OEM manifold will work, I think I might experiment with one. I haven't checked the port configuration yet, so that might necessitate either a new manifold, or go back to a new replacement R4. Thanks again for the input.

Dougflas on Tue August 28, 2012 8:34 AM User is offline

I had a 1988 Chev G20 van with the R4. I sold the vehicle a couple of years ago with over 100K on the clock. It had the original R4, R12 refrigerant and was still a quiet sounding compressor. The only thing I did was to replace a high side hose that was leaking. I did not replace the accumulator nor anything else. R4's were dependable as long as they did not run out of lubrication.

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