Carrier Furnace Blowing Control Fuse - HVAC - DIY Chatroom Home Improvement Forum

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Old 02-12-2007, 11:36 PM   #1
Join Date: Feb 2007
Location: Southern California 91741
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Carrier furnace control repeat problem

Carrier Furnace problem perplexing me too long.

Igniter,igniter control and thermostat replaced about a year ago by me.

Unit failed again about a month ago.

24vac transformer primary was open and replaced

Original control panel CES0110018 replaced by HH84AA020 by repair man

Repair man also replaced new thermostat
and said that igniter needed to be replaced again.
Lack of confidence in and seeminly too high charges by repairman, so checking out myself again, now.

There is a companion furnace of same model adjoining this one and trying igniter control in it checks ok.
Haven't yet cross checked the igniter or new main control panel in other furnace.

Started to suspect that the pilot coil on the gas valve was shorted, causing overload, but ohm checks between the two units shows no significant differences.

Fuse blows repeatedly with various troubleshooting
If I recall correctly, fuse does not blow if gas leads are disconnected

Could the igniter/pilot unit be the cause of the overload?

Igniter control is LH33WZ512A
Igniter assembly is Part # LH 680 005

I can rationalize that if something upstream of the unfused control board could cause the control board and transformer to fail, but not the thermostat. Besides the "expert" replaced a programmable thermostat with an unprogrammable one!

Any help steering me to possible cause will be greatly appreciated.

Thank you


Last edited by Protean; 02-17-2007 at 02:00 PM.
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Old 02-18-2007, 12:26 AM   #2
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i would replace the gas valve.


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Old 02-18-2007, 03:30 PM   #3
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Hi Protean

The problem you have is a short in the low voltage circuit. To determine if the problem is the gas valve or whatever you must first determine the short type. If it is a pilot coil burned up you will get inconsistent readings on your meter, IE: meter will not be able to settle on an ohm reading. However if it is shorted to ground you may get a stable ohm reading, but the terminals will read to ground also. I am not going to try and diagnose the problem from the information given, but the tech. is just guessing at problem. My first suggestion would be to disconnect the thermostat wires at the furnace. Operate the furnace with jumper wires, this will let you know if its even in the furnace. You could very well have a shorted stat wire.

Good luck
Character is doing the right thing even when no one is looking. Intelligence is understanding and practicing the meaning of character.
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Old 02-18-2007, 06:47 PM   #4
Join Date: Feb 2007
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Carrier furnace blowing control fuse

Thanks Carrierman and jbac:

I have been troubleshooting with the stat disconnected and w/r jumpered. Furnace is not at my home, but will be getting back to it soon after I received a couple of suggestions.

Ran out of local fuses and trying to find more. 3A is not a common auto fuse and Radio Shack supply is exhausted (they closed a lot of their stores).

Will substitute gas valve from other furnace, after running more checks on resistance. Ran out of time and fuses before.

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