Hey guys,
Bought my place in December and doing a major reno. Not living there at the moment, thank God (as it is only about 15 deg F out now.
The furnace was working ok (minus short cycles, but that is the not the problem I writing about.)
So sunday I ripped out a window to replace it, but ran out of time, so I threw some vapor barrier over the hole for the night, and when I came back the next day, my furnace wasn't running.
Broke out the multi-meter, and found that I had line power going to transformer, but no control power coming out. Great..problem solved.
Bought a replacement, threw it in, and blamo...heat glorious heat. BUT it ran over the set point of the thermostat. I couldn't get it to shut off, and when I finally did get it shut off, it wouldn't fire up again.
Took the multi-meter out again, and found....No control power again! Line power is ok, but no 24 VAC.
I have read somewhere that transformers don't just die. If you find one has gone, troubleshoot further to figure out what is source of the problem. So my question is, before I go and throw in another $40 transformer, what is killing them?
Thanks in advance for the help,
Mike
Control Power In A DGAA07BDTA
OK, first let me give you the best kept secret in HVAC for homeowners.
ANYTIME you replace a Transformer, get an Automotive type fuse holder and an ATC 3 amp fuse.
Install it in the hot wire on 24V secondary side of xfrmr.
It prevents ANY future xfrmr blowouts from low voltage shorts.
With that said, you have a short on the low voltage side.
Check ALL low voltage wires to see if any are touching neutral wires (bare) or touching metal.
Look closely at where the t-stat wires enter the furnace through the side of cabinet.
Something ~may~ have gotten in and chewed on a wire also.
Test for 24vac from the neutral side wire and a good ground.
Take care and best wishes,
Robert
ANYTIME you replace a Transformer, get an Automotive type fuse holder and an ATC 3 amp fuse.
Install it in the hot wire on 24V secondary side of xfrmr.
It prevents ANY future xfrmr blowouts from low voltage shorts.
With that said, you have a short on the low voltage side.
Check ALL low voltage wires to see if any are touching neutral wires (bare) or touching metal.
Look closely at where the t-stat wires enter the furnace through the side of cabinet.
Something ~may~ have gotten in and chewed on a wire also.
Test for 24vac from the neutral side wire and a good ground.
Take care and best wishes,
Robert
Some people are Humbly Grateful, while some are Grumbly Hateful.................... Which one are you ?
Robert,
It worked. Many thanks, and my apologies for not posting sooner, but I only have internet access at work right now.
The short was in the T-Stat wiring. Because I am in the middle of a reno, some of the t-stat wiring was laying on the ground, and I accidentally stepped on it and crushed it into the threads of a screw.
Also found somebody had replaced the "No More than 3 amp fuse" on the control board with a 7.5 amp. I probably wouldn't have burnt out the transformer if the proper fuse was installed. :S
Anyhow, thanks again for pointing me in the right direction.
Mike
It worked. Many thanks, and my apologies for not posting sooner, but I only have internet access at work right now.
The short was in the T-Stat wiring. Because I am in the middle of a reno, some of the t-stat wiring was laying on the ground, and I accidentally stepped on it and crushed it into the threads of a screw.
Also found somebody had replaced the "No More than 3 amp fuse" on the control board with a 7.5 amp. I probably wouldn't have burnt out the transformer if the proper fuse was installed. :S
Anyhow, thanks again for pointing me in the right direction.
Mike
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