I have a Rheem gas pack that recently started to malfunction, here is what's happening, the gas heat is coming on and getting hot, but the fan will not come on when fan mode is in Auto, I have been switching fan mode to manual on, just to cool down the heat exchanger, fan is working ok in manual on, and I suppose I could leave the fan running constantly but herein lies the problem, as soon as I switch the blower motor from auto to manual on, the A/C compressor also kicks in, and Its in both heat and cooling modes at the same time, this is an intermittent problem that only occurs maybe once, every two or three weeks, the thermostat has been replaced, the problem seens to correct itself after turning off the unit for half an hour or so. I have had two different service tech's out to diagnos the problem but they cannot find the fault because its working ok by the time they get here, they suggested I leave the unit on so they can troubleshoot the problem, But Im afraid to leave the heat on, it seems to get pretty Hot! without the fan running. Hope you Experts can offer a solution to this crazy problem. Thanks
DO NOT run it w/o a fan or you will damage the heat exchanger and have a huge problem. Sounds like you need a new circuit board as the heating fan relay is sticking. Turning to ON energizes G and there must be a short to the Y or backfeed which is another problem with your board.
"Cut it twice and it is still too short".