Coleman Furnance Question

[arcticcat18]

Had problems with my Coleman furnace, sorry I don't have the model number here with me at work. I will post that later. The furnace is an older model, 1992 ish. I have had a service tech here to work on the furnace, let me tell you the story.

Call for heat sent to the furnace, furnace would light the burner and run for a period of time, then the burner would go out, fan would not start. Upper limit switch kept 'popping' off. rest the limit switch and the fan would kick in. Tech replaced the limit switch, said it was old, and it worked fine for a few cycles. Then it started the same thing over again. Call for heat, burner lights, goes out, but fan would not kick in, tech replaced a fan switch. Then one night, a week later, the furnace fan was making a bad screeching noise, then locked up. Tech came out and replaced my fan motor, motor had locked up.

Today, the furnace still does not operate correctly in my mind. There is a call for heat, the burner lights and burns for a bit then it goes out. After the burner goes out, the fan kicks in anywheres from 10-50 seconds after that. While the fan is running, the burner will kick back in again. The tech told me that this is normal and that there is no problem with this type of operation. Does that seem normal?? The last thing I can add is that the furnace fan does not run on a timer, the tech did tell me that. Initially he felt it might be a timing issues with a fan timer, but that wasn't the problem.

[Robert]

On a call for heat, the burner will remain lit for duration of cycle until t-stat is satisfied.


All the parts changeouts chasing problem tells me that the Tech is fishing for problems .


What you described is not normal operation.


How long have you lived there and did it act that way before problems began ?




Thanks,
Robert

[arcticcat18]

We have lived here for about 2 years now. I dont ever remember it operating this way when we moved in. The Model number is a 7995C856.

[Robert]

First thing I would suggest is to get a Tech competant in troubleshooting HVAC systems and preferrably knowledgeable in MH units as well.


When the burner goes out prematurely, it is either a gas/air problem or an electrical interruption.


You can place meter leads on the gas valve and monitor it to see when the burner goes out, did you lose the 24-28VAC signal to the gas valve ?


Be sure when the burner goes out, that the t-stat had not been satisfied meaning the burner went out early.



Thanks,
Robert

[arcticcat18]

The t-stat should not be satisifed, as the blower had not yet kicked in and the t-stat itself is located nearly 35 feet from the furance. After the blower kickes out, and the motor kicks in, the blower will reignite and run for close to a 5-10 minute cycle before it shuts down again.

I can check the electronics, I just need to know what I need to buy to do it and where to check it at (ie what wires etc.) I am a bit mechanically inclined when it comes to this stuff.

Thanks!!

[Robert]

Do you have a wiring diagram and know how to read it ?

You test at each connection point from gas valve backwards to transformer.

Low voltage circuit = 24-28VAC.

Main Line voltage = 120VAC.

You would need a multi-meter to check electrical connections for proper voltage from gas valve back to power source (transformer).


If further step by step troubleshooting help is needed beyond the basics given, then you will need to go here first:


http://www.mobilehomerepair.com/Order4b.html


The $20 fee covers 1.5 hours of one on one email conversation.


If it is not an electrical problem, you will need a competant Tech to test the gas/air side for proper combustion and ignition specs.



Thanks,
Robert