hillybilly ac next step

bigkev on Fri July 02, 2010 4:21 AM

Year: 1990
Make: chev
Model: c1500
Engine Size: 4.3
Refrigerant Type: 134
Ambient Temp: 98
Pressure Low: 55
Pressure High: 275
Country of Origin: United States

to make a long story short this ac system on this truck is super hillbilly. The truck did not come with ac, so I pieced together all new parts to make it happen. I however am at the point that im not happy with its performance. I never did think ccot systems felt very good. better than nothing i suppose. I would like to try a vairable orifice tube because i believe in theory this would elemintate the problems of ccot. But I hear they have reliability issues. What Im wanting to do is put and expansion device on it to help control pressurres better. Brand new serpentine style condensor was adapted to fit and seemed to help a lot with getting to like 12 performance. But I want super cold all the time even at idle. Fan situaltion is good cuz i got 2 extras running when ac on. Ive been charging it like i charge houses by calculating superheat.

1. So could you guys think of a good universal expansion valve for my next rig ?
2. Who makes the best r4 compressors? or, better yet who has the best warranty?
3. Does anybody have a exploded diagram to this compressor? And/or where to get parts. Dont tell me about the tools or cost, I dont care.

mk378 on Fri July 02, 2010 7:22 AM

CCOT systems should operate at zero superheat (both evaporator lines same temperature or even outlet slightly colder) -- so you're probably undercharging it. Unlike a house system, it is OK and expected for some liquid to leave the evaporator since it will be caught in the accumulator.

Try different size fixed OT before giving up on the concept entirely. Looks like you should go smaller on the orifice. Practically any auto TXV could be used but if you convert to TXV you'd want to add a liquid receiver and also cycle on temperature not pressure or use a variable compressor.

The R4 was not GM's finest hour. Fitting some other model onto the engine would be the best thing to do about the compressor. A V7 is a nice unit with good capacity and the variable system can be used with either CCOT (just OT as it would never cycle) or TXV expansion.

ice-n-tropics on Fri July 02, 2010 12:38 PM

CCOT A/C should have zero superheat in and also out of evap. Because out is lower pressure than in due to evap coil pressure drop, the outlet will be a few degrees colder.
Opportunities for cooling improvement on older GM system are:
1) reduce or eliminate the 30% fresh air bleed into the blower while in the max (recirculated air mode)
2) Insulate accumulator like late model GMs. Not recommended on steel accumulators because of rust.
3) Add 100% hot water shut off valve in heater hose to reduce unwanted reheat
4) insure factory oil quantity but not a pinch more
5) Stop hot engine air from recirculating into condenser while idling
6) Add cab insulation (firewall, roof etc.)
7) Add exhaust heat shield
Cordially,
hotrodac

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Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy.
AMAZON.com: How To Air Condition Your Hot Rod

bigkev on Sat July 03, 2010 1:11 AM

Man, you guys are all right. Im gonna try some of this stuff out and try the way you guys suggested on charging. Ill tell you how it works out.

bigkev on Sun July 18, 2010 3:09 AM

ok, ive did most of these things including rigging up a heater control valve to help stop the reheat, accumulator wrapping , recharged with r12, new fan clutch. Im kinda happy at idle now but i have one more concern. 800 to 1100 the compressor has been growling at me. Went to the junkyard and got a different one and it sounds almost the same just a little quieter. Could to much oil make an r4 sound like this? Im having touble finding any exploded views of this compressor. Ive got bits and pieces and it looks like these have reed valves on top of the compressor. Ill bet u 10 dollars they used the old valves in the rebuilt compressor. I think maybe i replaced junk with junk. I wondered if it was the bracket but i just put it on with new bolts and locktite and even replaced a missing brace that i didnt have. If you grab the hose i can feel vibration from the compressor real bad. Both of the compressors feel real smooth when i turn them by hand. Does anybody know where i can get parts for rebuilding an r4 (I know your going to tell me not to). Ive done a few auto transmissions and they turned out good, so maybe i can handle an ac compressor to, dont worry about tools either im mcguyver. Im thinking the reeds are making this noise but before i spend 8 hours figuring out how to take this apart i want to know where i can get parts.

GM Tech on Sun July 18, 2010 8:26 AM

Those steel horseshoe brackets on the front of your engine provoke the growling-- there are brace kits that were available under TSBs when your truck was under warranty back in early 90's. We fought hard to eliminate that growling- even usedinertia pulleys- butbottom line is to install the brace kits- and make sure all bolts on horsehoe bracket that attaches to engine are tight-- this is what the compressor attaches to - so when compressor is off- look for all the bolts, make sure they are tight - and none are missing on the horsehoe bracket.--that is th ekey to the growl...

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

bigkev on Mon July 19, 2010 4:32 PM

Did heads a few months ago, Never put bottom bolt back in the compressor. I put it in and the growl is almost 0! Thank you! Keep it simple stupid right?