I need help troubleshooting Rheem RAHE-036JAS, Armstrong G1N80AU125D20C-1, Honeywell ST9160B 1068 Board, Honeywell SV9520H 8034 Gas Valve. About a week ago, AC and Heat were working fine. After power failure (could be coincidence), AC problem, Heat working fine. Symptom: No Inside blower. Outside AC Fan and compressor appear to be working fine. Inside blower will not run. Refrigeration line from AC to house will eventually begin to frost so I believe everything outside is OK. Thermostat: Originally had "Mechanical" AC/Heat thermostat (Lux T101143/PSM40). With Thermostat Heat/Off/Cool switch set to Heat, and Fan AUTO/On switch set to AUTO, Heat runs normally: Inside Blower/Fan is off, gas valve turns on, furnace ignites. After some delay, Blower starts and runs normally. Then, set Thermostat Heat/Off/Cool switch to off. Gas valve turns off, Blower continues to run for a while, then Blower shuts off. With Thermostat Heat/Off/Cool switch set to Off, and Fan AUTO/On switch set to On, Blower runs normally (continuous).

With Thermostat Heat/Off/Cool switch set to Cool, and Fan AUTO/On switch set to AUTO, outside AC fan and compressor start and run normally, inside Blower never starts. parts of an air handling unitWhile outside AC fan and compressor are running, turning Fan AUTO/On switch to On has no effect (inside Blower remains off).air handling unit for sale Discovered that Thermostat Fan AUTO/On switch seemed "loose". air conditioning fan will not turn onWith covers removed from Thermostat and baseplate exposed, fan switch operation was intermittent. I didn't suspect the Thermostat was responsible for the AC No-Blower issue but since the Fan AUTO/On switch was intermittent, I replaced the Thermostat with a new digital thermostat (Honeywell RTH2300 B).

With new Thermostat, no changes observed... Heat still working, and Fan/Blower (alone) still working, and No-Blower with AC On. AC outside fan and compressor still appear to be working fine. At this point, I have completely disconnected the ST9160B 1068 Board, and have marked and removed all wires, and have inspected it for any obvious issues but it appears to be fine. My thought is to thoroughly test the ST9160B 1068 Board. For example: reattach power, jumper Y to R and check for operation of on board relay, etc ... To do this there may be various sensors/interlocks that need to be checked/bypassed, so I'm looking for a procedure that will allow all this to be checked. If you feel I am looking in the wrong place, please let me know. Here are some pictures of the wiring diagram/schematics from inside the furnace door: And here is a picture of the Honeywell ST9160B 1068 Board: I reinstalled the ST9160B (Fan control) board and reattached all the wires except the R - C - W - Y - G wires which I left disconnected.

I verified the blower/fan wiring and it was as Tester101 said: A Black wire was on the COOL terminal. The Black wire runs the blower on HIGH speed. A Blue wire was on the HEAT terminal. The Blue wire runs the blower on MEDIUM speed. A Red wire was on the M1 terminal. The Red wire runs the blower on LOW speed (lowest speed). A Yellow wire was on the M2 terminal but this wire was capped at the other end (non-functional). The wire is used for fan motors that have a MEDIUM-HIGH speed... mine does not. The M1 and M2 terminals are not connected to anything on the circuit board. They only serve as a place to "Park" the blower motor wires that are not used. First I placed a jumper from G to R and depressed the interlock switch to allow power to the system. After a very short delay (about one-half to one second), the inside blower/fan started up. I checked the voltage on the HEAT terminal and found 120 VAC. Next I placed a jumper from Y to R (now Y&G are jumped to R).