electric furnace, blowing, but no heat, intermittent

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  #1  
Old 12-10-09, 03:23 PM
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Post electric furnace, blowing, but no heat, intermittent

I have a Goodman A30-10 that is about 20+ years old (1987 is the copyright on the Instructions). It has serial number "910610432". Trouble with not heating.

The symptoms, experienced mostly overnight - went to bed, furnace heating the house just fine. Wake up in the morning, house is cold, 10+ degrees below the setpoint. Thermostat is calling for heat and blower is running. FWIW, I have a digital thermostat (Hunter 44550) - it's in the HOLD position and not cycling a program. [Throughout all of this the FAN switch at the thermostat is in the AUTO position.] At the thermostat, I turn the switch to the OFF position (from the HEAT) position, and wait ten seconds. Then I move the switch back to the HEAT position and a few minutes later the heater kicks on and I can feel the warm air coming out. Depending on the setpoint and the outside temperature, dozens of minutes later, the house is up to temperature and everything is fine - I can hear/feel the unit cycling on/off depending on how cold it is outside - at least until the next extended period - typically overnight.

It does not seem that I have a Fan Limit Switch since when the thermostat calls for heat, the blower immediately comes.

I took some pictures of the unit's electrical compartment, if that might help.

Thanks for any pointers.
 
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Old 12-10-09, 04:38 PM
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From the serial number I suspect that your furnace was made in June of 1991, the date on the instruction manual is only the date the manual was written.

Many electric furnaces do not have a fan control but have the fan come on as soon as the thermostat calls for heat. It is done that way to prevent overheating the elements.

Pictures may help. Pictures need to first be uploaded to a photo hosting site such as photobucket.com and the URLs posted here. A good clear picture of the wiring schematic would be helpful.
 
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Old 12-12-09, 08:37 AM
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Unfortunately, the schematic that is in the Instructions is oriented towards the thermostat hookup (1 stage, 2 stage) - I can post a link if you think that would help.

Might anyone have further insight into what component I might want to test or replace?
 
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Old 12-12-09, 10:51 PM
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electric furnace, blowing, but no heat, intermittent

Any progress in figuring out the cause? I have the same issue with a Carrier electric furnace from ~1987 (model no. 40AQ901200). I've been experiencing this issue for ~1 year, but it comes and goes so I haven't been compelled to dump money into it yet. I have spent several hours trying to trouble-shoot it on two different occasions (most recently, just tonight). With the power off I: (a) checked the sequencer (measured 54 ohms across the heater terminals; and measured open across switches); (b) checked the coils (verified continuity across coils; and no continuity from coil to ground); (c) checked the limit switches (removed wires, verified continuity). With the power on I: (a) checked the sequencer (verified voltage across terminals with no call for heat; no voltage across terminals when heat was called); (b) checked output of transformer (verified between 22-28V).

I'm beginning to suspect the Honeywell digital thermostat...it's a thermostat that I installed about 3 years ago.
 
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Old 12-13-09, 09:04 AM
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I had heard that Hunter brand thermostats are not of good quality - maybe that's my problem. On the other hand, you have a Honeywell that is said to be of good quality.

I should see if I still have an old mechanical single setpoint thermostat to test the "bad thermostat" theory.
 
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Old 12-13-09, 01:05 PM
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Thermostats can usually be bypassed easily. The red wire is usually power and the white wire is usually the heat control. If you have a two-stage thermostat then the white is usually the first stage of heat and the second stage is designated W2 and might be any color. Connect red and white together and that will initiate a call for heat.

Most electric furnaces will "stage" the elements so that the entire heat output does not come on at first. This is mostly to prevent a large surge on the electrical system but it also works to some degree to limit the amount of heat supplied to the house. The additional stages are brought into operation through a device called a sequencer and the timing may be as short as less than a minute per stage to several minutes per stage.
 
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Old 12-27-09, 06:54 PM
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I finally installed an old Honeywell mercury thermostat. I have the same symptom - when it's obvious that the thermo is calling for heat, the furnace is not coming on. A slightly different sub-symptom though, previously with the electronic thermostat, it would call for heat and then the fan would come on but the heating coils did not, now, with the mercury thermo, neither the fan nor the heating coils come on.
 
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