Old Intertherm Mac heater shuts off too soon

Questions about repairs and parts for Nordyne furnaces, air conditioners and heat pumps for manufactured homes including Intertherm, Mac and Miller brands. Click here for Nordyne parts.

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Have a 30+ year old Intertherm Model MAC1155 in my Dad's little Mobile Home. Replaced the limit switch (with help from here finding one) and thought all was ok, but seems it continues to cycle on and off too frequently.

After turning it back on yesterday (was off 3 weeks) it took a long time to get it up to a comfortable temp. I timed the fan starting out at approx. 15 seconds, shutting off (burner roaring) then in a min or two the fan would come back on for another 15-30 seconds. It finally worked up to blowing for 2-3 minutes then shut off and in 2-3 minutes the cycle would begin again.

I understand the cold air was shutting it down until it could heat back up, but after things warmed up, it should run until it reaches the right temp and then turn off for longer periods than 2-3 minutes. The H/AC service guy in the area is who replaced the limit switch last month, but has since thrown up his hands and has no more ideas as to the problem. Any suggestions?!?! (Am pulling out what hair I have left).

LabLuver
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It sounds to me like you still have a limit switch problems. If I am not mistaken there are 2 switches, a high & a low switch. Is it possible that the wrong switch was installed?
Someone better versed in furnace work should be along soon. Greg
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Hi,

Did you replace just a Limit Switch or a Fan & Limit Switch combo ?

Do you know the serial number, we need to know the date of manufacture as the parts changed 3 times during that period ?

Thanks,
Robert
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Thanks Greg & Robert for replying. I can't confirm the right limit switch was installed, but it was doing the same thing it was doing before it was installed (cycling on and off too frequently). It was a combo limit & fan switch.

Here's the kicker - it seems to be working beautifully now, so I pose this question: Would a sticking thermostat make a furnace do this? It had not been used in 3-4 yrs prior to Dad moving in and yesterday someone suggested the contacts might be sticking and I worked it back and forth several times. Either that corrected the problem or the room finally got warm enough to stop pulling in cold air. Any thoughts?

Robert, the serial number of the furnace is: N1155 MAC8 MY30 9. The old limit/fan switch had MAX-1165, MAC-1155 and 42001 on the back of it. Thanks for your input!

Labluver
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Sticking contacts can cause this and if it had not been used, may work itself out.

For your furnace, they make 2-3 different Fan&Limit Switches depending on the age.

Before Nov./1967, after Nov./1967 and after April/1973.

Thanks,
Robert
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Thanks Robert - am hoping it has worked itself out. But, for future reference, how do I determine the age should I need to replace the limit/fan switch?

Labluver
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Look it over good for the date on a sticker or label somewhere.

If it is not found, we'll call Nordyne and see if they can tell by the serial number.

Thanks,
Robert
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Thanks Robert! It's really nice to know you guys are here to help. Appreciate all the info and feedback.

Labluver
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Hi,

You're very welcome, glad we could help.

Take care and best wishes,
Robert
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