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I have an Intertherm MGH-055AB furnace in my mobile home. The heat cycle seems normal now that I replaced the fan limit control. One thing, about 5 minutes after the cycle the fan comes back on for about 30 seconds to remove latent heat, I assume. Is this normal?

Hi,

Probably removing residual heat which is not normal. Need to find reason why all the heat is not being removed during cycle.

It cools chamber down to fan control temp setpoint, but heat chamber heats back up again quickly,,,,,,,,,,need to know why.

Bad fan switch/control, on-off settings too close, dirty heat chamber ???????


I'd let an hvac tech inspect it to know at least what it is doing/not doing.


Then maybe can take care of it yourself or maybe not, but you'll safely know what is wrong.



Thanks,
Robert

Thanks Robert, have a HVAC tech coming by Friday morning. There's so many potential problems I need a trained set of eyes. This furnace is so old (1985) it has a manual door for outside fresh air. Been keeping it open but is there any time that it should be closed?

Thanks,
Jeff

Hi Jeff,

Not all the time and more so open during summer than winter. They can be good and bad, just depends.


Thanks,
Robert

Hi Robert,
Just a update here. The HVAC tech was here a week ago. Gave me thumbs up on my cleaning job and measured 0 ppm on the CO2. The tech agreed with you that closing the manual fresh air door at the furnace is no problem. Apparently the latent heat build up on these older (1985) Intertherm gas furnaces kicking in the limit for a short time is common about 5 minutes after a heat cycle. Bad news is that there is no longer a replacement burner available when this one goes bad.
I had a older Intertherm heat only thermostat that was set to .7 which the tech corrected to .4, the correct setting. I noticed too many short cycles, so today I replaced the thermostat with a heat only Honeywell T87. I'm about as happy as I'm going to be for now.

Thanks for your help!
Jeff

Hi Jeff,

You're very welcome, happy to help.



Thanks,
Robert