Before I buy a new thermostat, would appreciate input on my issue. There is a constant hum at the air intake. The a/c works ok but furnace does not come on. Turn the a/c off, the humming continues. Have to switch off breaker to get rid of it. Is it the thermostat. This is a 1994 5th wheel. thanks
I just replaced my themostat. I had a problem like yours if the AC breaker was turned on I could hear a hum, even if the thermostat was in the off possition. If I runed the switch to ac it seem to be ok, except if you waited the system would not shut off once it reach set temp. You could still hear the hum. The only way to stop it was to turn off the Breaker. I could lift the yellow wire on the themostat and hear a relay clicking.
IMHO, You could try to turn off the breaker and then lift the yellow wire on the t-stat and see if you hear a clicking noise. I replace t-stat and all is working great now. If you do understand what you are doing when working on your RV. IF not get someone else to fix it.
First, is the thermostat one that is independent of the air conditioner, mounted on the wall and which you can use to select either the air conditioner, or the furnace? If so, then it isn't likely to be the cause of noise that comes from the air conditioner. I don't understand what it is that makes you think the thermostat? What brand and model of air conditioner, thermostat and furnace?
If I am correct about the thermostat, then it sends a signal to a control circuit board that is located inside of the air conditioner. There are two fans, one in the air conditioner and a different one in the furnace. The only thing common between the two is actually the control circuit board and the thermostat.
Having trouble shoot more than one RV air conditioners, if that hum is from the area of the air conditioner, from your description I suspect that it is from one of the air conditioner's relays. That would explain why it will resent if you open the circuit breaker for the air conditioner.
If you were to take the grill off of the air conditioner's air intake you would be able to see the metal box that contains the control circuit board that the thermostat feeds and some other items. The blower for the cold air is up on the roof, under the air conditioner shroud, as is the compressor.
All I know is I had a Dual-therm AC with a T-stat that controlled both the heat and AC. One night after the room got down to the set temp. The AC fan shut off, but I could hear a low hum noise, I which I was not use to. I move the T-stat control to off. The hum would not stop. I moved the T-stat to heat and before the furnace cam on I could still hear the AC hum. I turned the furnace off. I shut off the AC breaker off and the noise stopped. At home, I tried the AC again, First with the switch on the AC off, wehen I turned on the breaker I could hear the hum, even with the t-stat in off. I turned off the Breaker for the AC. Openned up the T-stat. With the AC breaker off, I removed the Yellow wire on the T-state marked cool I could hear a relay clicking. Even with the breaker turned off the AC relay was getting power with the T-Stat in the off possition. I then turned on the AC breaker when the yellow wire was on the T-stat terminal I could hear the hum, when I removed the T-stat wire the hum stop. If I moved the T-stat switch to AC ON with the yellow on the Terminal The AC would start up like normal. When I lifted the wire it would shut down.
I replaced my T-Stat with a digital on I bought at Wal-mart put it in and all is working like it should. All I am saying is a bad T-Stat could give you the same type of problem. The T-stat at W-M cost $20. A control board will cost more than that.