Gas and Oil Home Heating Furnaces - Blower fan constantly runs
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07-12-00, 10:15 AM
We have noticed the fan for the a/c constantly runs, the compressor kicks on and off, but even if we shut the system off at the thermostat the fan still runs. I have replaced thermostat already. Last night I removed the cover from the bottom of the furnace and noticed a little black box with dials that have settings for fan off/on time, is this the fan control relay? I looked for a label but to no avail...
thanks
thanks
07-13-00, 07:13 PM
That has the potential to be a number of problems. I'm assuming that the switch on the thermostat that says "fan auto/on" is in the "auto" position.
Could be any of the following:
A scraped wire in the thermostat wiring
A fan relay that has stuck in the run
If there is supposed to be a time delay in the system, that could fail to release.
That box you describe may be for the furnace, especially if it's gas or oil, the numbers would be for the temperatures that the heat exchanger must reach for the fan to turn on and off. It _could_ be some sort of adjustable time delay module, however...
A simple experiment is to flip off the breaker for a few minutes, then turn it back on. If the fan stays off, them I'd guess sticking relay. If it comes back on, it could still be any of the above.
Could be any of the following:
A scraped wire in the thermostat wiring
A fan relay that has stuck in the run
If there is supposed to be a time delay in the system, that could fail to release.
That box you describe may be for the furnace, especially if it's gas or oil, the numbers would be for the temperatures that the heat exchanger must reach for the fan to turn on and off. It _could_ be some sort of adjustable time delay module, however...
A simple experiment is to flip off the breaker for a few minutes, then turn it back on. If the fan stays off, them I'd guess sticking relay. If it comes back on, it could still be any of the above.
07-13-00, 10:27 PM
Hi:mikef
That switch you found is the fan switch. I do not suggest you adjust the settings.
However, another test is to hand smack that switch lightly with the back end of a screwdriver. If the fans shuts off, the switch is defective and should be replaced.
Best way to run this test is using the heater. This same fan switch also contains an A/C relay in most units. Which means the test may also be done when the A/C is used and the fan won't turn off.
Give it a try and post back the results.
Good Luck,
TomBartco
Natural Gas Energy Technician and Consultant.
Personal Quote:
"Drive Safely. The Life You Save, May Be Your Own."
That switch you found is the fan switch. I do not suggest you adjust the settings.
However, another test is to hand smack that switch lightly with the back end of a screwdriver. If the fans shuts off, the switch is defective and should be replaced.
Best way to run this test is using the heater. This same fan switch also contains an A/C relay in most units. Which means the test may also be done when the A/C is used and the fan won't turn off.
Give it a try and post back the results.
Good Luck,
TomBartco
Natural Gas Energy Technician and Consultant.
Personal Quote:
"Drive Safely. The Life You Save, May Be Your Own."