Goodman gas furnace

Problems related to residential installations.

Goodman gas furnace

Postby paw paw » Mon Jul 04, 2011 9:52 am

I have run into a problem that has me puzzled. Maybe someone can help. This unit was running just fine before this couple went on vacation for two weeks when they returned the unit would not run .
the unit is blowing fuses, I checked control wiring at hp unit, t-stat, and connections at the furnace there's no damaged wires, there is no visual(front or back) damage to control board.....so I completely disconnected control wiring from furnace replaced fuse, turned on power and it blew fuse, so I checked voltage at transformer 26.9v. There is only 2 components in the furnace control board and the transformer. Is the control voltage to high or is the board bad?????
paw paw
Regular Contributor
 
Posts: 12
Joined: Wed Jun 01, 2011 10:13 am

- Goodman gas furnace

Postby nomadpeo » Tue Jul 05, 2011 11:40 pm

maybe i misunderstood, but did you disconnect all external low voltage wires from stat and cu ? if you did and it still blew a fuse, it must be the board. your secondary voltage is fine.
nomadpeo
Most Valued Contributor
 
Posts: 278
Joined: Wed Jan 12, 2011 10:10 pm

- Goodman gas furnace

Postby heatseeker » Thu Jul 07, 2011 11:24 am

just curios how can you have 24 v at the t-former if you keep on blowing fuses? How are you able to check voltage at all at the unit?
heatseeker
Most Valued Contributor
 
Posts: 542
Joined: Wed Jul 06, 2011 9:10 am

- Goodman gas furnace

Postby nomadpeo » Thu Jul 07, 2011 8:07 pm

the secondary of the transformer is the voltage source. the fuse is on the board. if it blows, the transformer secondary voltage is still present. the fuse senses overloads in the circuit and opens the path to the voltage source.

after rereading, i'm convinced the board took a hit during that period, possibly lightning in the area. after isolating the low voltage wiring, if the fuse blows with power present, the board is the most likely problem. typically the transformer secondary will be slightly higher than the 24 volt nominal rating.
nomadpeo
Most Valued Contributor
 
Posts: 278
Joined: Wed Jan 12, 2011 10:10 pm

- Goodman gas furnace

Postby paw paw » Sun Jul 10, 2011 9:48 am

Thanks Guys, just needed a second opinion, this was was exactly my thoughts the board was the problem, OK now I unplugged the big plug on the control board, leaving the control wiring connected and the fuse did not blow. so does this mean there's a short in the internal wiring or maybe a some kind of limit switch maybe bad, at the furnace.
paw paw
Regular Contributor
 
Posts: 12
Joined: Wed Jun 01, 2011 10:13 am

- Goodman gas furnace

Postby nomadpeo » Mon Jul 11, 2011 12:27 am

we would typically expect a problem of this type to be the board or an external device such as external wiring or external load like the contactor coil. by isolating the external field connections, you ruled out those items. you have seemingly ruled out the cirucit board. of course, as you know, things are not always as they seem. the limit loop is a logical suspect if you were running heat, but i'm assuming you were in cool mode and heat was not running during this unmonitored period ? the 'divide and conquer' approach is sound, but still does not rule out the board. i think i would isolate power and test low voltage pins to ground with the plug isolated using an ohmmeter. maybe you do have a short to ground on one of those pins. good luck. let us know what you find.
nomadpeo
Most Valued Contributor
 
Posts: 278
Joined: Wed Jan 12, 2011 10:10 pm


Return to Residential