Heil CUGI100AF01 sleeps for 48 mins then starts up as expected

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Old 03-17-08, 09:57 PM
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Heil CUGI100AF01 sleeps for 48 mins then starts up as expected

Heil furnace from 1992 (BTUH input 100k, output=76k)

BACKGROUND
-Current outside temp=-1C
-A/C coil inside furnace and installed in 1992
-Furnace located in a furnace room pulling air from outside for combustion. Added extra vent from the basement area to increase air but no impact to the problem.
-Rotating drum humidifier connected to furnace like usual
-water tank located in same room as furnace installed last FALL
- put new air filter, vacuum blower motor
- 2 CO detectors installed in the house. not beeping as expected
-limit switch stays steady at 150-160. Limit is 180 and not reached when heating.
- 2 story house
- furnace has never needed a repair


PROBLEM
Furnace heats house but at times (seems random) the therm calls for heat but the furnace does not turn on. No clicking, no burners, no blower. Then after a while the furnace turns on without any intervention. Only noticed it a few days ago and could have been like this for a long time.

Real Observation:
10:47pm Thermostat clicks 'heat on' with hold76. Current temp=72. Furnace does not startup. However if I press "FAN ON" @thermostat the blower will turn on. I left it at "FAN AUTO"

11:25 Thermostat still shows "HEAT ON". Furnace just starts up on its own without any manual intervention (after 38 mins)

Furnace runs fine until 12:05 when the thermostat clicks off once the temp=76 and the fan continues to run for another 3 minutes.

I then raised the thermostat temp and the furnace started again as expected.

Another instance when the furnace was sleeping. I turned the power switch off, then opened the furnace and fan doors/cover. then closed it back and turned on the power switch and the furnace started as expected.

Any suggestions what might be wrong or other things I should observe to narrow this down ?

many thanks in advance
 

Last edited by automan1900; 03-17-08 at 10:39 PM. Reason: more info
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  #2  
Old 03-18-08, 03:15 AM
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What type of fan-limit control you have?
(pls give MFR & M/N)

Maybe you have a problem similar to the one shown on the following thread. Take a peek at it.
http://forum.doityourself.com/showthread.php?t=337590
 
  #3  
Old 03-18-08, 10:33 AM
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Limit switch is HQ613748HW.

A while back I noticed that the limit switch was hitting because the filter was clogged. Would repeated hitting of the limit cause it to shorten its life?
 
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Old 03-18-08, 02:02 PM
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It's possible that it would weaken, but not too likely.
What are the current settings?
Fan-OFF =
Fan-ON =
Limit =

I believe you may have given me a Heil part number, but not necessarily the limit's model number.
What company makes it? it should be engraved on the control itself.
 

Last edited by pflor; 03-18-08 at 03:48 PM.
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