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I have a Coleman Evcon Model: DGAT056BDC. The blower cycles on and off frequently during operation while the burner remains lit. I have replaced the fan limit switch several times to no avail. When the thermostat calls for heat, the burner ignites, heats the chamber, then the blower comes on. After that, it acts as if the chamber gets cool enough to turn off the blower, but with the burner still lit, the chamber heats up and turns the blower back on after a short period of time. At the end of the cycle, the blower usually turns off as soon as the burner is extinguished (instead of staying on for a while to cool down the chamber). I also just noticed that the data plate on the furnace indicates that it is setup for natural gas, but the furnace has always run on propane. I don't know if this could be related to the problem or not. Please advise.

Just a shot in the dark, but I think the flame would be yellow if a natural gas orfice was being used.
My oven's orfice kit came with their size stamped on them. The wrong orfice might also make the flame less hot, as well as leaving gas unburned. I'd sure verify the flame is burning right. It shouldn't have been connected to an LP tank without the gas provider checking it. I dont know what size your unit needs.
I'm sure you'll get REAL help here soon.

Have you tested the fan switch to see if it is opening ?

Inspect burner orifice/spud behind gas valve for blockage ( spider-web-bugs).


Thanks,
Robert

What size is the orifice currently installed? I've been looking at the same model furnace, supposedly set up for propane, but verification of the actual size of the orifice could be useful. I'm not in a position to check right now, but I think the propane orifice was stamped 082. There is a natural gas orifice in a little bag hanging from the gas valve, but I can't recall the number on it at all.

The owner says the furnace has never produced what might be considered hot air, just kind of warmish. I can say that I've dried my hands at a warm air drier that put out hotter air than any of the registers in this trailer...

LP = .082

NG = .128



Thanks,
Robert

The orifice is clear of blockages and is stamped .082 so the furnace must have been converted. Yes, the fan switch opens each time the blower comes on and closes each time it cycles off, even after installing a brand new switch.

The fan switch may be getting cool air across it cooling it down to open. May take an hvac tech to diagnose what is happening.


Thanks,
Robert