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Old 10-22-2011, 05:05 PM   #1
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Trane - Not Powering Thermostat


Chain of events:

2 night ago, we had a power surge. The system wasn't on (cool/heat).
Last night, got a bit stuffy so I switched it from "OFF" to "Cool" and went and did something. House wasn't getting cool, so I took a look at the thermostat, and it was blank (no segments, like no power). It was JUST on before because I noted the temperature on the thermostat.

Went through the usual paces. Checked all breakers (garage and by heat pump outside). Nothing was tripped.

This morning, I pulled off the fan from the heat pump and found some more chewed wires by rodents, but nothing was disconnected. Now, when I was fooling around I noticed that the control board had 1 green LED that was continuously blinking. This time, I pulled the panel off and the LED was off completely.

I did some searches, I checked the 60A breaker on the handling unit, and it was ok. Still no thermostat power. Figure out that there needs to be 24VDC to turn on the thermostat.

The control board on the heat pump has 120VAC going in. But for the life of me, I can't read any DC output from any point on the control board. My gut instinct is telling me that the control board transformer is bad, but I can't figure out the part number. All I can see is a couple of relays:



Control PCB PN: CNT04695

Any guidance/suggestions?

I'm new to HVAC, I'm an aircraft avionics tech by trade.

Thanks!

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Old 10-22-2011, 05:13 PM   #2
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Trane - Not Powering Thermostat


first off everything is AC not any at all DC.... Some times there is a 3 or 5 amp fuse in the air handler on the control board or inline from the transformer. Check that.

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Old 10-22-2011, 05:14 PM   #3
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Trane - Not Powering Thermostat


There's a transformer in the unit but not on the control board. It'll look like one of these.

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Old 10-22-2011, 05:27 PM   #4
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Trane - Not Powering Thermostat


Here's some more info for you guys:

Trane Heat Pump# 2TWB303A1000AA

Here's a pic of the what I guess is the transformer. There are 2 other wired components are the caps. I start and one run?



I read 120VAC at all 3 terminals (Black lead to ground). Uh, if this was the transformer, I'm going to assume that it should read 24VAC?

Also, the compressor comes on when I depress the contact which is just above this transformer. I know the unit operates, but with no thermostat it doesn't matter?

Thanks for the input and helping!!!!
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Old 10-22-2011, 05:43 PM   #5
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Trane - Not Powering Thermostat


Not the transformer, a relay.
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Old 10-22-2011, 05:43 PM   #6
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Trane - Not Powering Thermostat


Guess I missed where the transformer actually is:

The transformer is actually located behind the contact relay where I couldn't initially see it.

Meter at the transformer terminals and reads 0VAC to ground and across.

PN: C147094P02 or 3100-15Q242
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Old 10-22-2011, 05:44 PM   #7
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What airline do you work for, I want to make sure I don't use them.
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Old 10-22-2011, 05:45 PM   #8
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Quote:
Originally Posted by Doc Holliday View Post
What airline do you work for, I want to make sure I don't use them.
HAHAHAHAHA.

Been a long day what can I say? That's what I get for not looking good enough for accurate feedback eh?
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Old 10-22-2011, 05:49 PM   #9
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Trane - Not Powering Thermostat


Quote:
Originally Posted by Splitz300 View Post
Guess I missed where the transformer actually is:

The transformer is actually located behind the contact relay where I couldn't initially see it.

Meter at the transformer terminals and reads 0VAC to ground and across.

PN: C147094P02 or 3100-15Q242

Any old general purpose 120 volt step down transformer will work, they all do the same thing. Just make sure that if you get a multi step down transformer you hook up to the correct high voltage input wire. It will be stated on the transfomer, color coded as well.

It will not matter on the low control voltage side hooked to the unit.
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Old 10-22-2011, 05:52 PM   #10
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Trane - Not Powering Thermostat


Quote:
Originally Posted by Splitz300 View Post
HAHAHAHAHA.

Been a long day what can I say? That's what I get for not looking good enough for accurate feedback eh?

Glad you took that with a grain of salt.

I had trouble wiring in a friggin' heat sequencer yesterday, hooked the low voltage right to it's own common. Smoke, right in front of the customer.
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Old 10-22-2011, 05:53 PM   #11
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Trane - Not Powering Thermostat


Quote:
Originally Posted by Doc Holliday View Post
Any old general purpose 120 volt step down transformer will work, they all do the same thing. Just make sure that if you get a multi step down transformer you hook up to the correct high voltage input wire. It will be stated on the transfomer, color coded as well.

It will not matter on the low control voltage side hooked to the unit.
Do these typically go bad like that "all of a sudden" in the manner originally described? Unit is only just over 5 years old.

I could understand the contact relay going bad before a transformer, but I'm not an expect in these (obviously). I can force the system on by depressing the contact in the middle of the relay block.

Does the control board require 24VAC to illuminate the LED?
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Old 10-22-2011, 05:56 PM   #12
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Trane - Not Powering Thermostat


You said you had a power surge. In that event yes, that'll definitely do it. Other than that a short in the wire can take it out.
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Old 10-22-2011, 05:58 PM   #13
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Quote:
Originally Posted by Doc Holliday View Post
You said you had a power surge. In that event yes, that'll definitely do it. Other than that a short in the wire can take it out.
Guess I could pull the relay block and see if the transformer windings are melted or burned etc etc.

I've learned quite a bit. Cost me $89 last week in a service call for a tech to tell me there was a chewed off wires from a rodent which wouldn't allow the compressor/fan to turn on (low side switch?).

I looked at all wires in and out of that damn system, and I don't see anymore broken/chewed wires.
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Old 10-22-2011, 06:10 PM   #14
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Trane - Not Powering Thermostat


Are you looking for the transformer in the outside unit?
The transformer is in the inside unit. There will also be a fuse in the 18 gauge red wire.
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Old 10-22-2011, 06:11 PM   #15
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Trane - Not Powering Thermostat


Yup, dogs love chewing on those wires as well.

Last month I went on a call back, our company had installed a new evaporator coil and one month later the system wasn't working. The tenant, an elderly woman in her seventies, had a stroke while there. Mind you we were in a record heat wave here in Texas, over 30 consecutive days of over 100 degree ambient (outside) temperature. Inside a home it can be devastatingly hot in those conditions. People do die down here in the Summer, more than I'd like to admit.

The home owner was irrate with us, telling, no, yelling at me, how he was going to sue and this and that, yadda yadda yadda.

I go and check it out and sure enough the dog had chewed the control wires at the condenser outside, nothing wrong with the install.

Shut him the heck up really quickly!

I'd be wiling to bet he was blue in the face on the other end of the phone.

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