Interesting
My FSM (87,88,91) all show a diode in the resistor modules in the wiring diagrams for A/C but no diode on heater only. OK but the microfiche for 87,88,89,90 all mention the same part number for A/C vs no A/C, note that each use may use different part numbers. 91 uses different part numbers for A/C vs no A/C.

What happens if a non-diode resistor module is used in a A/C vehicle? I can always solder a diode into the wire harness, if need be.

I do notice at times my A/C starts with the A/C button off. Perhaps I have a flaky AC switch. I thought I would ask before I dug in too deep.

What do you think?

Car is my 87 Ti Peabody