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
Old Intertherm Mac heater shuts off too soon
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
Someone better versed in furnace work should be along soon. Greg
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
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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