Furnace cycles multiple times

Problems related to residential installations.

Furnace cycles multiple times

Postby TomtheElder » Sat Dec 29, 2012 4:15 pm

Short -
20 y.o. Carrier Crusader furnace (model 28CR042000) runs through its on-to-off cycle repeatedly, with a new cycle starting immediately – no pause at all – after the end of the previous cycle (see video at *.*/watch?*...*.be ).

I assume this is hugely inefficient – any ideas what could be the problem? Thanks.

Long -
The cycle in the video completed in - but the duration is not consistent. I timed another as -
TIME ACTION
- Furnace starts
- Pilot light glows
- Burner on
- Blower on
- Burner off
- Blower off

Immediately upon finishing the cycle a new cycle will start; there is zero pause between the end of one cycle and the start of the next. I think it typically will run through 8-10 cycles before shutting off. There may be times of as few as 4-5 cycles. This morning I counted 20+ cycles in one run – but that might have been affected by things like doors being opened.

Near the end of the 20+ cycles this morning I timed two consecutive cycles; each took -. After being off for a while it restarted and I timed the first cycle at -. Clearly the length of the cycles varies, possibly becoming shorter through the sequence of cycles.

HVAC system was installed in 1991 and has not had any repairs. Here is the embarrassing part – this problem has occurred since at least fall of last year (I timed one cycle then at -) but I can’t say for certain when it started. Any ideas as to what may be causing the problem will be hugely, hugely appreciated. Thanks.

Tom
TomtheElder
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- Furnace cycles multiple times

Postby Freon » Sun Dec 30, 2012 12:03 pm

First step is eliminate the thermostat as a cause. Turn off the power to the furnace. At the furnace, place a jumper wire between the R and W terminals. This will call for constant heat without any thermostat intervention. Now TEMPORARILY turn on the power knowing the furnace will start. See if the cycling happens. If the furnace runs without cycling, check the batteries in the thermostat. If the furnace cycles then we need to look at other causes of the shutdown.
Freon
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- Furnace cycles multiple times

Postby TomtheElder » Sun Dec 30, 2012 3:21 pm

Freon, thanks for the sugestion - I will give it a try.

Tom
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