Janitrol garage heater

I have a Janitrol Garage heater and have what I believe to be a fan/thermos tat problem. The unit's pilot lights fine, the unit fires up fine, after30- 45 seconds the fan comes on. BUT the fan runs for 10 seconds, shuts off for 15 seconds, comes on for 10 seconds, shuts off, etc etc. it'll do this for hours, after several hours once the garage warms, the unit will sty on. Ba d thermostat? any help is appreciated. (I bought this unit on Craigs list a nd owner said it worked fine previously)
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On 12/11/2013 1:30 PM, snipped-for-privacy@comcast.net wrote:

I don't know your particular unit, but gas heaters like that have a thermostatic fan limit switch switch that controls the fan. It will turn the fan on when the heat exchanger reaches a certain temperature, turn it off if it is too cool to blow heated air to the room.
It may be adjusted wrong, it may be defective.
This may give you a rough idea where to look
http://www.youtube.com/watch?v=BhENuaQ4nLk

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