Working on a dinosaur
Have a Goodman GMP125-5 furnace connected to an old coil. Originally had blown 3amp fuse. Replaced. When call for cooling fan relay way humming really loud and transformer dropped from 24v to 13v. Upon return 2 days later found unit dead, 120v to transformer nothing on other side. Replaced transformer. When call for cooling the led light on board goes out, blower runs, then inducer starts and runs. Nothing at condensor. When call for heat inducer runs, hsi glows, gas valve clicks nothing comes out. Thermostat is a complete Frankenstein job of 8wire tied to 2 separate 3 wires to tstat. When nothing calling the led stays solid, jumping r to g gets blower to run consistently. I’m wondering if it’s the board dropping the 24 when getting a call and going into some kind of safety. Any advice would be appreciated