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Billy
Billy, HVAC Technician
Category: HVAC
Satisfied Customers: 19781
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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I lost my low voltage to my thermostat. I replaced the transformer

Customer Question

I lost my low voltage to my thermostat. I replaced the transformer today with a generic from the local carrier shop. I am getting 28volts to the R and C on the thermostat but am getting an E2 error message? Any suggestions?
Submitted: 5 years ago.
Category: HVAC
Expert:  Mark Henley replied 5 years ago.

Hi,

 

What brand and model of thermostat is it ?

 

Thanks

 

Mark

Expert:  Mark Henley replied 5 years ago.

Hi,

 

I found the info,

 

"E2" on temperature display Brownout condition or too low of voltage to thermostat. Double check wiring and check for
24 vac between R and C. E2 will clear 15 sec after proper voltage is restored.

 

Thanks

 

Mark

Customer: replied 5 years ago.
AS I mentioned eariler, I am getting 28volts between R and C. The transformer is only putting out 120V to the orange wire which is supposed to be 220?? I know the fan in 200 and the capicitor for the fan is 300+ volts. If the tranformer is only putting out 120V would that cause an E2?
Expert:  Mark Henley replied 5 years ago.

Hi,

 

I understand that you are getting 28 volts,,

 

Is this a heat pump air handler or a gas furnace ?

 

Thanks

 

Mark

Customer: replied 5 years ago.
Heat pump. Thanks
Expert:  Mark Henley replied 5 years ago.

Hi ,

 

Is the transformer a 220 to 24 or a 120 to 24 ?

 

Thanks

 

Mark

Customer: replied 5 years ago.
Yes. Bought it from the local Carrier shop in McKinney Texas. It is a generic and was 60 dollars cheaper than the original. It has 2 wires for the 24V and on the other side has orange for 230, white for common, black for 110 and red for 208. have the 110 and the 208 wire nutted separately and using the orange 230
Expert:  Mark Henley replied 5 years ago.

Hi,

 

I really don't know what the problem may be , the E2 error means that there is low voltage present at the stat, apparently the stat believes there is low voltage there and will not reset itself. You may end up replacing the stat., I will leave this question open for some of the other experts to look at also.

 

Thanks

 

Mark

Customer: replied 5 years ago.
OK. Maybe the same thing that knocked out the transformer did something to the stat too. I can get another from the carrier shop. Just wanted to rule out anything else before I purchased. Parts are non-returnable. Thanks for trying. Eric
Expert:  Mark Henley replied 5 years ago.

Hi,

 

No problem.

 

Thanks

 

Mark

Customer: replied 5 years ago.

Mark,

 

I replaced the thermostat with another from the my other unit that is working and it gave me the same E2 message. So I am guessing it is not the stat. Maybe the 24V relay outside could be shorted and dropping the voltage to the transformer??

Expert:  Mark Henley replied 5 years ago.

Hi,

 

If you have 24 volts at the stat it should work, there are a couple of good Carrier guys here but they probably won't see this until morning.

 

Thanks

 

Mark

Customer: replied 5 years ago.
Thanks. I will check back tomorrow
Expert:  Billy replied 5 years ago.

Hello,

 

Just helping Mark..

 

I had a customer do this same thing and his 24 + and 24- were reversed. He put the transformer in and it simply fed the voltage the wrong way and the stat did not recognize.

 

May be your problem....maybe not...but worth checking.

 

Billy

Customer: replied 5 years ago.
Guys, tried reversing the polarity and got no display on the stat. Reversed them back and got display again but same E2 message. Eric
Expert:  Billy replied 5 years ago.

Unhook at the furnace...W, Y, G.

 

leave only the r & c hooked up.

 

See what that does,

then add w

then g then y

 

w=heat

g=fan

y=condensing unit outside

 

see if it is one of thos efunctions in the common side

Customer: replied 5 years ago.
Sorry, before I had received your response I cut power to ouside unit at breaker to check that relay. The E2 message went away and I do get all functions at the stat. So it must be something out there...the relay with the 24V coming off it??
Expert:  Billy replied 5 years ago.

I would check the 2 wire for any nicks ,rubs or contact with metal.

 

you can discon the coil wires from the contactor..turn off discon...pull the 2 24v wires from the contactor, and see if message leaves.

 

obviously then if the short goes away with the contactor out of the loop, replace contactor...if still there, it is in the 2 wire.

 

But if it went away with power off.....Bad contactor

 

Billy

Customer: replied 5 years ago.
I know it is late but here is an update. Turns out I don't have a short in the wires to the outside unit from the attic. Tested the wires open and for continuity. I am getting 25V outside until I put it under load of the relay. Thought ok, the relay must be bad. Replaced the relay...same thing. Took the relay up to the attic. Hooked in directly to the 24V output from the transformer and it worked fine. Then connected it to the 24V output from the PCB in the attic and was 25V until I connected to the relay...Do you think the problem is with the PCB in attic? Everything in front of the PCB seems good, after the PCB...25V until under load. The PCB has blown several 5 amp fuses but I thought that was due to the short I thought I had to the outside....PCB is around $300.00 with a non return policy...just want to be as sure as I can. What do you think? TIA Eric
Expert:  Billy replied 5 years ago.
Put the relay in and hook up wires. Leave wire at pcb at C off. noe we have 24 v going from unit to stat, from stat to condenser, and condenser back to pcb but not hooked to common. If no short....pcb...if short...it is still out there somewhere.
Customer: replied 5 years ago.
Thanks for the reply. Let me make sure I am understanding you. You want me to hook the relay back in to the outside unit. Take the red wire to the PCB "C" going out the PCB to the ouside unit off, check with VOM if there is 24V to the stat, then 24V from stat to condenser, and 24V from condenser back to PCB in attic. If all check out 24V it is not the PCB, if not 24V to all then something else?
Expert:  Billy replied 5 years ago.

That is correct. What happens,

 

24 v leaves transformer

24v arrives at thermostat

thermostat decides what function

thermostat sends 24 v to air handle "cool"

air handler "cool"sends the 24v to outside

outside condenser receives 24 at the contactor

24v now leaves contactor to head "home" to common

24 arrives at C for common at the pcb

the pcb sends 24 v common on transformer.

 

So that is the journey the 24v took until it arrived at C. We want to interrupt the 24v just before it reaches C on the pcb and see if there is no short. If fuse is ok with C unhooked, we know we do not have a short to ground. If it blows fuse hooked to C, then pcb bad

 

Sorry to ramble so much but I try to simplify the circuit.

Billy, HVAC Technician
Category: HVAC
Satisfied Customers: 19781
Experience: Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
Billy and 5 other HVAC Specialists are ready to help you
Customer: replied 5 years ago.
Much appreciated. Eric
Expert:  Billy replied 5 years ago.

I thank you Eric and I am available for follow up on this project at no charge for you.

 

Thanks again

 

Billy

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