Orok2500
Junior Member
- Joined
- Aug 10, 2026
- Posts
- 1
- Reaction score
- 0
- Location
- CA
- First Name
- Brian
- Truck Year
- 1978
- Truck Model
- K2500
- Engine Size
- 350ci
Truck: 1978 GMC K2500 Sierra, 350, 4x4, long bed.
Someone did a partial AC delete on this truck before I got it — compressor, condenser, receiver/drier, and the entire evaporator box are gone. Blower motor and cab-side ducting are still intact, and the truck did have factory AC originally.
I picked up a take-off AC/heater box + A6 compressor + harness + ducting from an '87 C10 for $150 (confirmed the box itself has the evaporator core and an accumulator attached, corroded but solid). I'm not running the A6 — building a Sanden 508 conversion instead (bracket, harness adapter, and compressor already sourced).
Before I get into it, wanted to ask: has anyone here actually swapped an '87 box into a '78-'80-era truck specifically? I know the general firewall-hole-alignment process (self-tapping screws to position, drill new 5/16" through-holes, patch mismatched holes with a plate), but if anyone's done this exact year pairing I'd love to know:
- Did the '87 box's mounting holes line up reasonably well with a pre-'81 firewall, or was it a lot of new holes?
- Any surprises with the electrical connectors between an '87 harness and a '78 factory harness?
- Anything about the dash-side ducting/control head that didn't translate cleanly from an '87 to a pre-'81 dash?
Appreciate any real experience — trying to avoid finding out the hard way.
Someone did a partial AC delete on this truck before I got it — compressor, condenser, receiver/drier, and the entire evaporator box are gone. Blower motor and cab-side ducting are still intact, and the truck did have factory AC originally.
I picked up a take-off AC/heater box + A6 compressor + harness + ducting from an '87 C10 for $150 (confirmed the box itself has the evaporator core and an accumulator attached, corroded but solid). I'm not running the A6 — building a Sanden 508 conversion instead (bracket, harness adapter, and compressor already sourced).
Before I get into it, wanted to ask: has anyone here actually swapped an '87 box into a '78-'80-era truck specifically? I know the general firewall-hole-alignment process (self-tapping screws to position, drill new 5/16" through-holes, patch mismatched holes with a plate), but if anyone's done this exact year pairing I'd love to know:
- Did the '87 box's mounting holes line up reasonably well with a pre-'81 firewall, or was it a lot of new holes?
- Any surprises with the electrical connectors between an '87 harness and a '78 factory harness?
- Anything about the dash-side ducting/control head that didn't translate cleanly from an '87 to a pre-'81 dash?
Appreciate any real experience — trying to avoid finding out the hard way.
