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homeschoolfun5 · May 2, 2008, 11:15 AM

We moved into this house 2 years ago. We were told the heating and a/c unit was fairly new. The unit is outside on the roof. It is an American Standard unit. When the inside thermostat is on "off" and the fan on "auto," the fan comes on by itself, stays on for anywhere from 5 to 90 minutes and then just shuts off. Is this normal or is there a problem? Over the phone, a repair man said it sounds like the "relay" is bad. Got any information on this? He said it would cost about $130 to fix. Can we check it ourselves and fix it ourselves? Thank you.:confused:

hvac1000 · May 2, 2008, 10:05 PM

Since the unit is so new it is possible that the thermostat is causing this to happen. Many new thermostats has a setting for allowing air circulation for a set period on time with out the heat or A/C being turned on. What is the brand and model number of your thermostat.

homeschoolfun5 · May 3, 2008, 09:52 AM

The thermostat in the house old. It is probably the original one from 1963. The name brand is White-Rogers. It has a lever to indicate "cool," "heat," or "off." And the other lever is for the fan and the options are either "auto" or "on." I have the temperature lever on "off" and the fan lever on "auto." I would think that the fan would stay off as there is no temperature indicated as the temperature lever is in the "off" position.

What do you think??

hvac1000 · May 3, 2008, 12:52 PM

It sounds like you do not have a newer thermostat so we can take that off the table as a possibility for now.

Since this is random in nature as far as timing goes I would next suspect a wire rub through or shorting problem. This happens from time to time on the thermostat wires that go from the thermostat to the unit.
I would first check right behind the thermostat and at the wall where the wires enter.

While you have the thermostat off the wall I suggest you label and disconnect the wires and let it be for a few hours to see if the blower stops blowing by itself.

If it continues to blow at random replace the wires exactly where they came from and remount the thermostat to the wall.

The next place to look is on the unit itself. Label and disconnect the thermostat wires on the unit on the roof and wait a few hours to see if the blower stops running.

Do this and post back with your findings.

homeschoolfun5 · May 4, 2008, 06:53 PM

Thanks. I'll get to it and get to you.

homeschoolfun5 · May 8, 2008, 06:36 PM

I undid the wires to the thermastat inside and the fan still kicked on. It was really interesting having to figure out how to take the thermastat apart and to turn off the electricity going to it as it had a hot wire.

I just shut off the electricity to the whole HVAC unit so I don't have to listen to that fan. Plus I am saving the $$$ of it being on so much.

I haven't had the time to go onto the roof. It sounds foreboding.

I will go after it and get back to you . Thanks again.

hvac1000 · May 8, 2008, 07:13 PM

Remember you only did one step by removing the wires from the theromostat. I would say now that the thermostat is OK but there could still be a short in the thermostat wires from the thermostat to the roof unit. If you disconnect the wires in the roof unit and it stops running then you will know the short is in the thermostat wires. If after disconnecting the thermostat wires in the roof unit the blower still comes on once in a while then you know it is in one of the controls for the blower in the unit itself. Happy hunting.