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Dean958 · Jan 21, 2013, 10:02 AM

My blower comes on for 30-45 seconds and stops. The limit switch does not reset. Then it rests for a few minutes and starts the cycle over.
Thermostat is set for 90 on unit and is about 1 year old. Wall thermostat is digital and about a year old as well set for 68. It is almost 50 in here vurrently

Coleman 7975A856 Direct Vent Forced air. Presidential, Natural Gas

mygirlsdad77 · Jan 21, 2013, 05:36 PM

Wow, there are so many problems with the way you described your problem that I don't think anybody would be able to help you.

Which blower? Which limit? And there is no thermostat on the unit, so what is set at 90? (completely lost me there). Only part that makes sense is that your wall stat is set to 68. Going to need a lot better description of what is happening to be of any help.

Dean958 · Jan 23, 2013, 02:25 PM

Originally Posted by mygirlsdad77

Wow, there are so many problems with the way you described your problem that I dont think anybody would be able to help you.

Which blower? Which limit? And there is no thermostat on the unit, so what is set at 90? (completely lost me there). Only part that makes sense is that your wall stat is set to 68. Gonna need a lot better description of what is happening to be of any help.

Well as far as I know there is only one blower in a forced air Furnace such as this one. The limit switch is the upper limit switch. The thermostat is in fact another piece all together which the last tech replaced with a universal and it looked like a variable thermostat switch. Which is in fact the fan switch.

Replaced both parts last night. Issue now is, the limit switch pops (might be a bad limit switch I got from the place) but the blower is not turning on when I put the program on automatic (IE I set it to XX degrees after 430am) it heats but doesn't blow and pops the limit switch now. It seems to be doing it with both limit switches so possibly yet another problem with the furnace.

Hope that helps and an fyi, please be a little less abrupt when condescending someone next time, thanks. I am a chef not an HVAC guy, so while I can tell you how to technically cook a steak and understand the difference between blanching and searing, I am not privy to part names in a furnace.

mygirlsdad77 · Jan 23, 2013, 05:10 PM

So the blower is never kicking on when the stat is calling for heat? That would cause the limit to trip. Can you check to see if the blower motor is getting roughly 120v when it should be kicking on? If the motor is getting voltage but not running, it may be as simple as a motor run capacitor, or you may need a complete new motor. If no voltage to the motor at any time, you will need to trace back the wiring from the motor to what relay, etc controls it. Hopefully the wiring diagram is still on the inside cover of the unit to help with this. Other than that, it will most likely be time to call the tech back. Must be an older unit, as most newer gas furnaces have two blowers, one induced draft blower (exhaust the combustion to outside), and one main blower (circulates the air throughout the home).

In your first post you say the blower comes on for 30-45 seconds, but in you last post it isn't coming on at all. This points to possible motor issue, or it could still be a capacitor, or even a relay problem.

Sorry about the bluntness of my first response, long days at work and I need to leave it there, not take it out here. Wishing you the best of luck with this problem. Let me know how things turn out.

Grady White · Jan 23, 2013, 07:44 PM

Very common problem with Coleman furnaces. Many use a thermal disc fan control. Most of the time when the fan switch is replaced the problem goes away. Several years ago Coleman had a recall for that exact problem. I did so many of them I could do the entire job, including functional test, in under 10 minutes.