I have a Goodman RTU that am having issues with. The model# is weathered completely away. It is an R-22, 5-ton, gas heat. The draft inducer motor is basically short cycling. It turns on for 1-1/2 seconds, then turns off. It is trying to make the circuit, but is failing. I have checked the wiring diagram, everything checks out. I have checked the high limit switch, it's fine. The compressor Model# CRN5-0500-PFV-970. Serial#01H03750B. I have replaced the circuit board because it had 2 burned out resistors. The inducer fan was initially running constantly in heat mode, now it can't make the switch. Any suggestions?