Looks like there is some interest in the AC system so here are some details of my quest for cool breezes.
The truck was retrofitted with a Sanden 9285 (R12) and a new dryer/condenser with O-ring fitting and new hoses at some point. When I bought truck there was no AC belt, pump was not aligned, as it would hit the fan. I fixed that and tired it out, it was still holding refrigerant (holy shit!). Didn't work well at all, added some R12 I happened to have, pressures OK, split sucked. Disconnected heater core, that helped a lot but still not great. Fan motor bearings were shot, wiring toast. Limped for one summer, better than nothing.
So trying to move forward on A/C system. For some reason I've been avoiding it. I drug all the crap out of storage but it has just sat for 3 months on my workbench. Usually I keep my bench clean and void of anything that is not an 'active project'. I hoped that the clutter would motivate. Not so much as I built a bumper instead.
I guess it is because each piece has a road block of some sort, so no easy progress on any aspect.
- All wiring burned out; fuse block, fan switch, A/C function switch
- Fan motor toast
- Defrost duct missing
- All foam and seals old, disintegrated
- Heater valve leaks, shot
- No room for compressor, hits fan. Have to move motor or mod pulley. No brackets, have to fab.
- No room for condenser, have to mod core and grill
- have to move dry/receiver, so need some new hoses
And with engine swap, need to build a new compressor bracket, but the comp clutch contacts the fan. Need to decide on solution for that before building bracket, although the bracket has to be adjustable somewhat. Can't move fan forward, as there is no room between radiator. So have to modify the crank pulley or move all the drivetrain back to allow fan spacer. Can't buy a 1/4" fan spacer, so have to make one. Can get a 1/2" spacer, but can't move motor that far. There are pulley shim kits that I could stack, but that is cheesy. Tried to cut down crank pulley in lathe, but my lathe is too small. I do want a bigger lathe, but, well, that is a whole different discussion.
The condenser doesn't fit in between trans cooler and grill, so grill mods and mount brackets will need to be built. The drier was mounted where the coil over tower is now, so need to find a new location and build a bracket. This will require new hoses to be made, or maybe a combo with hard lines.
I did put in provisions for wiring upgrades. I ran a dedicated 30A circuit for fan motor so current doesn't go through the main harness. Converting clutch control circuit to low current, just driving a relay to the EFI system. But EFI is active low logic so added inverter, and EFI has end control on A/C clutch.
So I started on rebuilding the HVAC box in the cab, gathering parts. Factory A/C parts are hard to find and expensive, so I repaired what I had. Fan switch also does A/C clutch control. Medium speed didn't work at all, high was intermittent. I pulled switch apart and cleaned contacts. Had to reshape the wiper to get robust operation.
The system has a switch to lock out compressor clutch when not in A/C mode that is actuated with one of the cables. It was also burned out due to the inductive nature of the clutch coil. When A/C is shut off, the magnetic field collapses and the stored energy produces damaging high voltage/current in the circuit. This switch will become isolated behind a relay, and relay protected with a 'flyback' diode.
The heater core is the last item to come out of the assembly, making it the worst thing to have to service. It wasn't leaking, but I pressure tested it and cleaned it.
The 72 factory A/C system was a retrofit into the space available and not the best solution. One aspect I wanted to improve was isolating the heat from the cool in at least 3 ways
-improved 4 port heater hose bypass valve
-Thermal insulation between cores
-Sealing heater core from low pressure side of fan assembly.
The heat side blend door seal was poor at best. If it leaks, air is drawn across the heater core and dilutes AC effectiveness. The goal is to get the door to seal with the limited amount of force the cable and linkage system can apply. Tried a few different types of gasket material to find one with the right crush. Since one seal edge is on the hinge (terrible design), it bunches up the seal in the pinch zone and prevents the opposite side from even touching, so I contoured the foam with roloc disc to get a nice fit.
The OEM seal design on the cool side door is also poor at best, but I don't care and left bare with no gaskets. Why? because the heater core provides plenty of BTUs and A/C can effectively be shut off. I don't care if air leaks across evaporator as it get pulled into fan. The result of leakage is just recirculating in cab air in heat mode.
But the real issue was that the linkage between the complementary heat and cool doors was too long, resulting in the heat door not being able to close all the way. So I shortened the linkage and adjusted the switch contact. This makes the heat door the assembly travel limit instead of the cool door.
Last step was some bubble insulation on the metal division wall between the cores. You can see here how the factory retrofit results in heat function pulling outside air only and A/C is recirculate only.
