Friday ~ March 03, 2010
I have an electric furnace that will not shut off unless I switch it to the off position. Once the temperature is met, it continues to run. I have replaced the thermostat. We also replaced a fan relay, and a transformer. Its acting the same way in air conditioner mode. Please advise. :)
sounds like the actual relay for the elements is stuck on. Will look like a stack of rounded things with clips on either side usually. Sometimes they are square but they all have wires between them and the element connection on one side and 1 side of the power supply on the other.
Be careful!! they only break 1 leg of the 240 volts, other leg will be hot!!! so be absolutely sure that you have the power turned off and then double check with a tester of some sort.
is it your fan (blower) that keeps running or the whole system. check your t-stat wires for a short. you will need a volt-ohm meter. with the power off and the thermostat wires off the thermostat check all the wires with each other. if there is no short it might be worth having a service tech check it out and give you an estimate. at least you will know what the problem is and if you can do it yourself. the cost of a service check is just a little more than a thermostat, fan relay, & a transformer. :) good luck
If by "switch it to off position" you mean at the thermostat then something in your 24 volt control wiring, or at the thermostat is mis wired or you have a short and Bill is right.
If off you mean off at the air handler and you are shutting off the power to the unit then latentraveler is probably correct, it likely a fused contact on the sequencer. The fan contact is usually marked.
But this is what meters and a schematic are for. You trace where the power is coming from and find a bad component or trace from there to find where the control voltage is coming from that is activating it to find the fault.
Good Luck
4 wire thermostat? Sometimes you need a jumper from one hot (R1, R2) to the other. Other times white may go to blue. I recommend a tech..for 25 bucks, they can fix you right up.
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