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need advice on new system for street rod

bnewsom on Fri July 20, 2007 9:21 PM User is offline

Year: 1952
Make: Chevy
Model: styline sedan
Engine Size: 425 Cad.
Refrigerant Type: 134A
Country of Origin: United States

Need some advice on how to proceed. I am building a 1952 Chevy Sedan Street Rod. It is powered by a 1976 Cadillac 425 engine. I was planning on using the original compressor which I think is the axial type (about 6" dia. x 12 or so inches long). Everything else would be new. Planned on using the largest parallel flow condensor I can fit in front of the radiator and a behind the dash ac/heat/defrost unit from Southern Air. Barrier hoses, filter/dryer and pressure switches would make up the balance of the system with 134A being the refrigerant. My question is should I use this compressor since I already have it or should I upgrade and pay several hundred more dollars for the sanden 508 and special mounting brackets? If I use this compressor, how should I prep it and can you give me some oil and refrigerant quantities. Thanks in advance.
Bob

bohica2xo on Sat July 21, 2007 1:56 AM User is offline

The OEM compressor on the caddy is an A6. One of the toughest, most reliable compressors ever made.

The SD508 would be considered a downgrade. Less capacity, no oil sump.

The A6 comes with great OEM mounting brackets too. The balance of the system you describe sounds fine. The A6 has enough nuts to run a dual system if you are thinking of rear air for that car...

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

bnewsom on Wed August 29, 2007 12:01 AM User is offline

Thanks for your quick reply and sorry for my late response. Just a couple more questions please, what oil and how much should I put in the compressor? When I talked to the A/C kit suppliers all are steering me towards using their sanden compressor claiming low power required to turn it vs. the A6 and of course, theirs is new. Should this be a concern?

Thanks Again,
Bob

ice-n-tropics on Wed August 29, 2007 5:27 PM User is offline

Bob,
The reason most Hot Rods use the SD508 (called SD5H14 for R-134a) is to balance the A/C component capacity. As Bohica said, it is less capacity (8.4 cubes verses 12.6) and it only retains about 50% of the oil in the crankcase at 1000 rpm.
The condenser must dissipate the heat absorbed by the evaporator plus the energy used to drive the compressor. Now there just isn't much real estate for a big face area radiator and condenser in a 52 Chevy. Also, a rule of thumb for a Hot Rod in high temperature climates is that R-134a works best with at least 20% more condenser capacity that a R-12 condenser. It is unlikely that you can stuff a Caddy size condenser in front of a Caddy size radiator in the 52 Chevy's OEM radiator width and also with Caddy velocity air flow. Make the widest frontal opening and radiator face area that is possible. heat exchangers gain the most capacity from face area, but additional thickness provides diminishing returns because the air is progressively heated as it travels from front to back.
If the evap has too much capacity and the compressor is too large, the heat dissipated from a monster condenser would preheat the air going into a borderline radiator above the Air-To-Boil (ATB) threshold.
Most Hot Rod A/C does not offer the outside air mode for evaporator inlet air because the entering hot humid air drives up the power draw and condenser heat load.
Adequate radiator air flow is a challenge for cooling a 425 engine in down town Phoenix traffic without trying to over kill the interior temperature.
Disclosure: I can obtain a professionally polished new/unused fresh SD5H14 for 1/2" drive belt left over from a 61 Pontiac job if you are interested @ $200.00.
Cordially,
Old IV guy

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

bnewsom on Wed August 29, 2007 10:16 PM User is offline

Thanks for the info. I didn't include some info about the car in my initial post because I didn't think it relevant. Shows you how much I know about the details of putting together a balanced system. The car has a 2nd generation Camaro subframe and the radiator support has been modified to fit a new full size Cadillac 3 row radiator which is supposedly the HD radiator for a 500 engine. The core alone is 28" wide by 18" high and has good airflow with proper shrouding and an engine driven fan. Plans call for installing the largest parallel flow condensor I can fit in front of this radiator. How much does this change things?
Bob

Edited: Thu August 30, 2007 at 7:04 AM by bnewsom

ice-n-tropics on Thu August 30, 2007 2:05 PM User is offline

Bob,
you're going to have adequate condenser and radiator to support the A-6 refrigerant mass flow pumping capacity. You may decide to use a smaller crank pulley or larger clutch to reduce the compressor drive ratio and improve derivability. Next problem is to get enough evaporator capacity to keep the compressor from cycling like a Banshee just to prevent evap freezing. Southern air may not have a 20,000 to 24,000 BTU evaporator to be in balance with the comp and cond.
Cordially,
Old IV guy

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

bnewsom on Fri August 31, 2007 9:15 PM User is offline

Thanks for the additional info. I am going to check with Hot Rod Air and others to see of their units are in the 20-24k btu range. If anyone has any experience with any of the hot rod oriented units feel free to comment.
Thanks agian,
Bob

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