# Trane - Not Powering Thermostat



## hvactech126 (Nov 11, 2010)

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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## Doc Holliday (Mar 12, 2011)

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


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## Splitz300 (Oct 22, 2011)

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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## Doc Holliday (Mar 12, 2011)

Not the transformer, a relay.


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## Splitz300 (Oct 22, 2011)

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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## Doc Holliday (Mar 12, 2011)

:jester: What airline do you work for, I want to make sure I don't use them. :thumbup:


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## Splitz300 (Oct 22, 2011)

Doc Holliday said:


> :jester: What airline do you work for, I want to make sure I don't use them. :thumbup:


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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## Doc Holliday (Mar 12, 2011)

Splitz300 said:


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


 
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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## Doc Holliday (Mar 12, 2011)

Splitz300 said:


> 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. :whistling2:


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## Splitz300 (Oct 22, 2011)

Doc Holliday said:


> 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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## Doc Holliday (Mar 12, 2011)

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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## Splitz300 (Oct 22, 2011)

Doc Holliday said:


> 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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## Master of Cold (Aug 7, 2011)

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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## Doc Holliday (Mar 12, 2011)

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! :laughing:

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


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## biggles (Jan 1, 2008)

the board receives 24V from the tr and then with the stat connected it controls the board and the out side condenser....the relays on the board control the fan 115Vs to run the fan either from the stat in cooling or FAN/ON off the subbase,or during the heating which could be a time delay on a call for heat the 2 black relays on that board are rated as you see..if anything is powered and you get a surge from the pole the weakest items will take a hit if you remove the old TR ring out both sides with the ohm meter setting see which doesn't have continuity thats what took the hit


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## Splitz300 (Oct 22, 2011)

Master of Cold said:


> 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.


The handling unit is in the attic, no fuse, just a 60A breaker which I reset a few times before this all started. There's a similar relay block as in the outside unit. 

I took off the relay block from the heat pump outside, not necessariliy a short, but showing 18Ω.


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## Splitz300 (Oct 22, 2011)

Doc Holliday said:


> 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.


Where in Texas are ya?!?!?!?!?!


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## Doc Holliday (Mar 12, 2011)

Splitz300 said:


> Where in Texas are ya?!?!?!?!?!


 
Deep in the Heart of it. 

Houston.


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## Splitz300 (Oct 22, 2011)

Doc Holliday said:


> Deep in the Heart of it.
> 
> Houston.


Ah, crap.

Oh well, worth a shot.

Just to confirm, the 24VAC Transformer is behind this contact relay:


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## Master of Cold (Aug 7, 2011)

"Houston, we have a problem"


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## Master of Cold (Aug 7, 2011)

That part pictured is the windings of the electromagnet, for the contactor relay. The transformer is in the air handler.


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## Splitz300 (Oct 22, 2011)

Master of Cold said:


> That part pictured is the windings of the electromagnet, for the contactor relay. The transformer is in the air handler.


Here's a pic of the air handler stuff.

There's a 60A breaker that has huge red wires going from the blower motor then to the outside.

I read 0VAC at all points.










Could it be something as simple as this breaker???

The contactor below that, when you hit the contact in the middle, turns on the heat...ask me how I know...LOL


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## Doc Holliday (Mar 12, 2011)

The only way to get 24 volts from 120 or 240 is through a transformer. Just because you don't see it doesn't mean it's not there. Look for the wiring diagram and find the tranny, it is there. Look by the blower.


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## Splitz300 (Oct 22, 2011)

:wallbash:









5A Fuse.

F M L

8 hours to troubleshoot to a fricking 5A FUSE? Are you kidding me? Glad I'm in aircraft repair and not HVAC troubleshooting. 

Well, at least I didn't have to spend $89 for said fuse.

I assume any automotive fuse will work?


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## Doc Holliday (Mar 12, 2011)

Any 5 amp auto fuse, yes. One and the same.


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## Splitz300 (Oct 22, 2011)

Doc Holliday said:


> Any 5 amp auto fuse, yes. One and the same.


In my haste of taking the fan off the heat pump, I don't remember what color wires go where.


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## Doc Holliday (Mar 12, 2011)

You're screwed now! 

take some pictures, good ones. trace back wires and take pictures there as well.


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## Master of Cold (Aug 7, 2011)

Black to defrost board, red to cap "c" terminal
Brown to cap "f" terminal.


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## Splitz300 (Oct 22, 2011)

Master of Cold said:


> Black to defrost board, red to cap "c" terminal
> Brown to cap "f" terminal.


I have puple, black, and brown. LOL


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## Master of Cold (Aug 7, 2011)

Don't feel bad. I know a guy whom is an awesome hvac technician. His personal truck broke down one day. After a fuel pump relay, ignition module, crank sensor and new cap rotor and wires, I went over and found out he was out of gas....


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## Master of Cold (Aug 7, 2011)

Purple in place of red


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## del schisler (Aug 22, 2010)

Splitz300 said:


> 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?


I bet that transformer has 110volt AC input and 24volt ac out thro diodes to make up DC voltage ?? i don't belive diode's work on AC voltage. I would look to replace the PC board it will be a complete board. May be exchanged Don't know the warrenty contact the mfd. and see and also ask about a PC board. Most likey the doide's are bad not the trans. But those are cheep transf. Check voltage on one side 110volt ac not on the other side 24volt ac now their should be some little diode's right around their also . With a ohm meter check frount to back and see if the reading is different? If the same they are shorted. Now they should be unsoldered one end and check that way. Best to just get a new board. Been in repair for 50 yrs. Now retired


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## Doc Holliday (Mar 12, 2011)

Master of Cold said:


> Don't feel bad. I know a guy whom is an awesome hvac technician. His personal truck broke down one day. After a fuel pump relay, ignition module, crank sensor and new cap rotor and wires, I went over and found out he was out of gas....


is this really true? what airline does he work for?..


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## Master of Cold (Aug 7, 2011)

Do you ever wonder about reading comprehension?


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## Doc Holliday (Mar 12, 2011)

I can't read so there's nothing to comprehend. :thumbup:


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