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Goodman HVAC system control problem- blown transformer



 
 
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  #1  
Old June 10th 08, 01:03 AM posted to alt.home.repair
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Posts: 2
Default Goodman HVAC system control problem- blown transformer

Hi, we have a 4 year old house and the upstairs AC thermostat suddenly lost
it's display. I switched the thermostat with the downstairs one and the
problem stayed with the upstairs unit. I received a tip that the 240v to 24v
transformer might be the problem, so I went up to the attic where the air
handler is and tested the leads on the transformer... sure enough, 240v in is
OK but nothing is coming out on the 24v side. So, I got a replacement
transformer and wired things back up. The display came back on, the unit
switched on and started blowing through the vents and I thought i had fixed
it.

BUT about 5 minutes later i went up to check on it and the display had gone
back out, so something is tearing up the transformers. I'm not an electrical
engineer, but I can't figure out what would burn up a transformer without
tripping the main breaker. Any ideas?

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  #2  
Old June 10th 08, 04:16 AM posted to alt.home.repair
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Posts: 677
Default Goodman HVAC system control problem- blown transformer


"dm440c" u44157@uwe wrote in message news:856ff33f86bde@uwe...
Hi, we have a 4 year old house and the upstairs AC thermostat suddenly
lost
it's display. I switched the thermostat with the downstairs one and the
problem stayed with the upstairs unit. I received a tip that the 240v to
24v
transformer might be the problem, so I went up to the attic where the air
handler is and tested the leads on the transformer... sure enough, 240v in
is
OK but nothing is coming out on the 24v side. So, I got a replacement
transformer and wired things back up. The display came back on, the unit
switched on and started blowing through the vents and I thought i had
fixed
it.

BUT about 5 minutes later i went up to check on it and the display had
gone
back out, so something is tearing up the transformers. I'm not an
electrical
engineer, but I can't figure out what would burn up a transformer without
tripping the main breaker. Any ideas?

Defective transformer, transformer voltage or current improperly rated for
the service, mis-connected, or overloaded. These transformers do not present
enough load, even when the secondary is shorted, to trip the main breaker.

Try another transformer, making sure it is for 240 volts and you have it so
connected. Some transformers have different leads for different voltages.
Also make sure the VA or current rating is at least what the original
transformer was. Monitor it carefully and if it seems to be overheating
check the secondary current to determine why it is overloaded.

Don Young


  #3  
Old June 10th 08, 04:17 AM posted to alt.home.repair
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Posts: 111
Default Goodman HVAC system control problem- blown transformer

Well, in most cases I'd wonder whether the transformer was the proper
VA rating. But in your case, I'm guessing you have a short between the
transformer and the upstairs T stat. That will blow a transformer
without tripping the breaker.



On Mon, 09 Jun 2008 23:03:12 GMT, "dm440c" u44157@uwe wrote:

Hi, we have a 4 year old house and the upstairs AC thermostat suddenly lost
it's display. I switched the thermostat with the downstairs one and the
problem stayed with the upstairs unit. I received a tip that the 240v to 24v
transformer might be the problem, so I went up to the attic where the air
handler is and tested the leads on the transformer... sure enough, 240v in is
OK but nothing is coming out on the 24v side. So, I got a replacement
transformer and wired things back up. The display came back on, the unit
switched on and started blowing through the vents and I thought i had fixed
it.

BUT about 5 minutes later i went up to check on it and the display had gone
back out, so something is tearing up the transformers. I'm not an electrical
engineer, but I can't figure out what would burn up a transformer without
tripping the main breaker. Any ideas?

  #4  
Old June 10th 08, 03:49 PM posted to alt.home.repair
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Posts: 148
Default Goodman HVAC system control problem- blown transformer

dm440c wrote:
Hi, we have a 4 year old house and the upstairs AC thermostat
suddenly lost it's display. I switched the thermostat with the
downstairs one and the problem stayed with the upstairs unit. I
received a tip that the 240v to 24v transformer might be the problem,
so I went up to the attic where the air handler is and tested the
leads on the transformer... sure enough, 240v in is OK but nothing is
coming out on the 24v side. So, I got a replacement transformer and
wired things back up. The display came back on, the unit switched on
and started blowing through the vents and I thought i had fixed it.

BUT about 5 minutes later i went up to check on it and the display
had gone back out, so something is tearing up the transformers. I'm
not an electrical engineer, but I can't figure out what would burn up
a transformer without tripping the main breaker. Any ideas?


When you replace the transformer again this time wire a inline fuse from the
transformer so when it shorts out again it will blow the fuse and not
destroy the transformer. Where you buy the transformer they should be able
to tell you what size fuse you will need. Then you can start to find what is
blowing your fuse. It does sound like when the A/C starts it blows then I
would check the wiring going to your A/C outdoors. You wouldn't believe how
many times I have seen a weed wackier had cut into the control wiring.
Good Luck.
--
Moe Jones
http://www.MoeJones.info


  #5  
Old June 12th 08, 03:17 PM posted to alt.home.repair
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Posts: 331
Default Goodman HVAC system control problem- blown transformer




Defective transformer, transformer voltage or current improperly rated for
the service, mis-connected, or overloaded. These transformers do not
present enough load, even when the secondary is shorted, to trip the main
breaker.

Try another transformer, making sure it is for 240 volts and you have it
so connected. Some transformers have different leads for different
voltages.


"Some?" Try ALL.

He should:

1) Ensure that the "next" transformer is nameplated for 240 (or whatever
the air handler is wired for) volts input or if it's dual voltage that he
uses the right wires and tapes off the unused wire(s). Many air handlers
use both 120 and 240 volts so he should determine which voltage the
transformer sees. It's quite common to use 120 volt fans even when all
the heaters are for 240 volts. If the fan motor is 120 volts, it's likely
that the control transformer is also 120 volts but nothing is certain.

2) Install a fuse on the transformer output rated for 80% of the nameplace
output current of the transformer.

Clearly "something is wrong" here.

The clamp on amp meter work just as well at 24 volts as they do at line
voltages. That might be a start.

It's quite possible that the transformer is underrated. It might have
enough juice to power the fan relay and the changover relay and the
compressor contactor. But if it's an especially COLD day and the system
calls for "suplemental" heat, it may have the energy to power the thermal
relays that bring on the heat strips. The supplement heat strips and
"sequenced" and the load (including the load on the 24 circuit) increases in
steps. If there is a short on the input of the last thermal relay in the
sequence you would never know unless the demand for supplement heat lasts
long enough to sent 24 volts to that last relay.

But I would definitely put a fuse on the 24 volt circuit while figuring
things out. It's better to replace a $.50 fuse than a $25 transformer.


Also make sure the VA or current rating is at least what the original
transformer was. Monitor it carefully and if it seems to be overheating
check the secondary current to determine why it is overloaded.

Don Young



** Posted from http://www.teranews.com **
  #6  
Old June 12th 08, 04:21 PM posted to alt.home.repair
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Posts: 5,109
Default Goodman HVAC system control problem- blown transformer

dm440c wrote:
Hi, we have a 4 year old house and the upstairs AC thermostat suddenly lost
it's display. I switched the thermostat with the downstairs one and the
problem stayed with the upstairs unit. I received a tip that the 240v to 24v
transformer might be the problem, so I went up to the attic where the air
handler is and tested the leads on the transformer... sure enough, 240v in is
OK but nothing is coming out on the 24v side. So, I got a replacement
transformer and wired things back up. The display came back on, the unit
switched on and started blowing through the vents and I thought i had fixed
it.

BUT about 5 minutes later i went up to check on it and the display had gone
back out, so something is tearing up the transformers. I'm not an electrical
engineer, but I can't figure out what would burn up a transformer without
tripping the main breaker. Any ideas?

Hi,
Checked fuse on 24V AC control voltage?
 




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