The furnace blower motor in my 1988 22ft Funchaser was squealing badly. I had to remove the furnace completed from the HiLo and replaced the furnace blower motor. If I remember correctly, there is more than one type on blower motor. Specifically, for my unit I needed a "Suburban 520950 Old Motor" that I purchased for around $95 on Amazon (However, I just checked and they are currently not available on Amazon at the same link. The replacement motor came with high level instructions on how to remove and install the new motor which was helpful! https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
The furnace model number will be located on the data plate and will begin with "NT", "GT" or "DD". The serial number will have nine digits. NOTE: Furnaces manufactured prior to 1990 will not have a nine digit serial number
I'm guessing but if your furnace is igniting correctly and running for some time as you indicate before blowing cold air it may be due to lack of sufficient air flow or high temp which actuates the gas shut off valve. See explanation below on how a furnace works and some trouble shooting tips. Hope this helps!
How A Furnace Works:
- A thermostat summons heat via a circuit board inside the furnace.
- After a short delay, the board activates a dual-purpose blower, injecting air into the combustion chamber while also moving air thru the ducts.
- A sail switch closes, signaling that the blower has enough air for combustion to occur.
- A gas valve is opened, admitting gas into the burner inside the combustion chamber, where an electrode assembly produces spark.
- Combustion occurs and gasses are vented outside.
- A limit switch halts gas flow if temperature is too high or if the blower becomes
- The thermostat controls furnace run time.
The most common malfunctions are generally related to one of two items:
- DC voltage and/or gas pressure.
- If the fuse panel is ok, use a 12v DC tester to check for power in the wires leading into the furnace. This will ensure that you have an uninterrupted power circuit.
- Check voltage to make sure it is adequate - at least 11 volts. Compare voltage at the battery and at the furnace. In weak circuits, voltage may drop as much as 1 volt between the battery and furnace, suggesting larger wiring is needed or battery is not capable of holding a charge.
- If the voltage is good, the problem may relate to the furnace circuit board, a relay, faulty blower motor, or another component such as the thermostat.
I recently ran across this article and thought I would pass the info on. Hope it helps you out.
2014 FR Heritage Glen 282RK
2013 F250 HD 6.7L Diesel
Formerly Owned: 1995 22D Fun Chaser & 2901L Classic