RV Repair: HVAC, amp fuse, suburban furnace

Question
I have a 2001 Springdale-Clearwater with a Duo-Therm model no. 57915.531 A/C unit and a Suburban furnace (not sure of the model), both ducted. I had a lightning strike somewhere near my home or to the power line. The trailer was pluged into a 20 amp receptacle on my shop (separate out building) and the furnace was set to come on at 40 degrees (I had not turned if off from the last cold spell). The main circut breaker for the out building was tripped and the circut breaker for the receptacle that the trailer was pluged into was tripped. When I try to turn on the A/C the compressor comes on but the blower does not. I can not turn the A/C fan on at the thermostat either. The furnace was out of gas, I attached a tank that was about empty, ran the three burners for about 2 min. and then attempted to run the furnace. It will not come on. I do hot hear the usual sounds of it trying to light nor will the fan come on. I have checked the 3 amp fuse in the control on the A/C unit (model no. 3107541.009) and it is fine. All breakers appear to be fine and everything else in the trailer is working. There is power to the thermostat. I believe it is either the thermostat or the control board in the A/C unit but I do not know how to tell for sure. The A/C unit had been run at the end of March, during spring break, along with the furnace and both worked fine. I have read that if the start capacitor for the A/C fan is bad you can spin the fan, with the A/C turned on, and if it starts that indicates the capacitor is bad. My fan is not accessable from below so I will have to climb on top and remove the shroud. I don't believe this is the problem though because neither the A/C or furnace are working. Not to mention that I am a rather large fellow (6'2" @ 245 lbs.) and my roof does not like me on it. I groans and pops when I climb up there. Any help or thought would be appreciated. Thanks!


Answer
Hi Lackey:
You certainly explained the problems completely. Let me see if I can help. Close lighning strikes can have serious results with electrical systems everywhere. Solid state devices are especially susceptible to damage and I think that most likely what happened to your unit. There are solid state devices in both the dual purpose thermostat and the furnace control board. I doubt very much that there is a start capacitor for your AC fan. Start capacitors are used in applications where the motor starts with a load on it like your AC compressor. In the freon circuit there is some amount of pressure in the compressor output side and it is that load the the capacitor helps to overcome. The fan has no load to start so I doubt it has a capacitor. You are correct that if a capacitor is bad you can start the motor by spinning the shaft. You could disconnect the thermostat wires and put voltage directly to the fan motor to see if it spins. Be carefull, the compressor is certainly AC voltage but the fan may be 12 v DC. The furnace is definetly 12 v DC. The DC power to the furnace control board comes from the thermostat. Check the furnace board to see what wire does what by unplugging the connestor from the board. The wire code is printed on the board. The power wire is usually the first wire, sometimes it is white, sometimes red. Check for voltage there. If you have voltage the furnace should start in about a minute or so, once the timer times out. Then the blower runs another minute or so before the furnace ignites. If you get no voltage there with the furnace switch on and the temp set to maximum then the thermostat is bad. if you get voltage there, or jump voltage to the power wire seperately, and it does not start then the furnace board is bad. My guess is that both the thermostat and the furnace boards were damaged by the lightning. There is also a similar control board in the water heater, you might check operation of that also. Good luck.
Bill