I've replaced almost all the A/C components in my truck, so I can give you an idea of how it would work.
- Blower motor and heater core were replaced with OEM components.
- OEM steel fan with severe duty fan clutch
- Evaporator is still original OEM, along with low temp probe and cutoff switch that is inserted into it. Evaporator was flushed to remove all old oil.
- Replaced condenser with largest parallel flow that would fit. After the fact I found out that the large OEM condenser may have been fine, but opinions vary.
- Replaced A6 compressor with a Sanden compressor and brackets from Vintage Air. Had to figure out the best belt length, but otherwise a straightforword job with my V-belt system.
- Replaced filter/drier with one from about an '85 truck, mostly because the top fittings lined up better. OEM could have been made to work, but the hose fitting was on the bottom.
- Added a high pressure cutoff switch, screwed into old R12 port fiting. Probably not needed, but recommended. You can just wire it inline with the original low pressure cutoff.
- Switched to Ford blue orifice. Supposed to work better than GM white with R134a.
- Had custom barrier hoses made up to connect from compressor to condenser and compressor to evaporator. They put the new R134a charge ports in the fittings where they connect to the compressor. Very easy to reach when charging.
- The lower evaporator fitting on a '75 is large diameter and it is where the orifice tube fits. They had to make a custom fitting (brazed two together) for that connection because its a small diameter hose but a large fitting. I think the orifice is in a different location on newer trucks.
- Reassembled with all new green O-rings, lightly lubed with PAG oil
- Recharged with about 7-8 oz of PAG oil and an R134a charge that is about 75% of the R12 charge. Used the gauges to tune the charge a little further, based on pressures.
This setup worked well for a couple of years, and then I had problems chasing down a leak. Leak turned out to be the body of the high pressure switch leaking - not what I expected, but I guess its a cheap switch. Currently running again and able to drop the temps down very quickly.
Bruce
