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    HankHayes's Avatar
    HankHayes Posts: 1, Reputation: 1
    New Member

    Apr 12, 2007, 05:17 AM
    Forced Air Furnace flame good, fan goes slow then fast then slow, etc

    I have a forced air propane furnace in a "Park Model" rv trailer. (This is a bit smaller than a mobile home) The furnace is used infrequently as the trailer is located in a sumer resort vacation area, however we do like to go up a couple of times in the winter months.

    Furnace was brand new in 2000 when purchased, and worked fine even in 15 degre below zero (it gets cold up in the mountains).

    This past winter a strange thing happened, when we fired the furnace up te first time it worked great, it reached the temperature set on the thermostat and cycled off. When it cycled back on, the blower never reached full speed, and what happens is the fan oscillates slower and faster continuosly.

    I have peeked into the furnace while this takes place and the flame inside is strong. The fan simply goes up and down and up and down and never reaches a good speed.

    The night this happened we turned the furnace off and used electric heaters.

    The following week I went up to try agan, and the same thing happened - with the furnace cold the first cycle was perfect. Once it kicked in a second time we are back to the oscillating blower!

    I waited a few days again, and this time it was very cold outside - I ran the furnace and set the thermostat high to see if the blower would oscillate if the furnace was running a long time - and it stayed the normal blower speed for the better part of an hour.

    I let the furnace cycle, and of course the oscillating began.

    The only hint I have right now is that my brother-in-law now tells me that this happened three years ago while he was using the trailer - and that he had the guy who sold it to us come out, and he got up on a ladder and did something to the chimney/exhaust pipe.

    That guy is no longer around, and my BIL does not remember what they said the problem or the solution was, but it might have been some flue maintenance?

    Any help will be appreciated! Thanks!
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
    Heating & Air Conditioning Expert

    Apr 14, 2007, 02:53 AM
    Check the exhaust for plugging or debris.

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