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Tim H.
Tim H., HVAC Professional
Category: HVAC
Satisfied Customers: 3971
Experience:  Experienced in all aspects of HVAC, both residential and commercial.
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Hi Tom, Im having a thermostat issue can you help?

This answer was rated:

Hi Tom, I'm having a thermostat issue can you help?

Tim H. :

Hi, I'm Tim and I'm an HVAC expert here to assist you with your questions. Please provide all information I request as it makes it more difficult to troubleshoot something when I'm not there onsite. Essentially, you become my eyes and ears. Thanks for the opportunity to help. At the end of our dialog, you will have a chance to rate my service, but please wait until we are finished and you're satisfied you have all the information you need.

Tim H. :

Hello there

Customer: hi, sorry ran to lowes.
Tim H. :

No problem/

Customer: Fellow at lows said I likely blew a fuse because I didn't turn unit off before I changed batteries. Control panel on unit appears operational, and thermostat appears to be cycling but nothing engages.
Tim H. :

Based on the symptoms you are describing, it sounds like you may not have gotten the thermostat firmly seated on the back part (called the subbase). It's also possible that you might have blown a fuse.

Customer: I'm pretty sure it is seated. The display is all working and it clicked in well. Maybe I lost a connection when I pulled it off but I checked the contact wires inside the thermostat. Stupid question - a fuse at the breaker box or a fuse on the actual air unit (inside or out?).
Tim H. :

It would be a fuse at the furnace or air handler (not sure which you have). The fuse would be on the circuit board

Customer: Ok, there is a control panel with a red light on the unit in the basement - red light is constant which I think means voltage is ok, but I don't see anything that looks like a fuse that I can check. Outside fan had a red reset switch that I tripped and nothing happened.
Tim H. :

Do you have a voltmeter? This would be the simplest way to check the furnace (or air handler)

Customer: I don't have one, but I see power is going to unit but can't test beyond that. Husband is checking to see if there is a fuse on the circuit board. I didn't see any but he is double checking. Any chance the thermostat could be bad even though it is behaving properly?
Tim H. :

Yes, that's possible. In fact thermostat issues constitute a good part of my service calls.

Customer: Everything was working fine before I changed the batteries. I think stupidly pullitng it off without turning off the system has caused a glitch.
Tim H. :

Let's try this: pull the thermostat off the wall, and doublecheck that your batteries are in correctly. Then reattach firmly to the back part

Customer: Tried 2 sets already. Reset the thermostat twice, even reverse polarity and tried again. But I will do again and cross fingers.
Tim H. :

Yeah, make sure they are going the right way because being in wrong could potentially damage the thermostat

Customer: They are in the right way. Earlier I tried reversing for 15 seconds as "trick" found on s forum. I think it was no better than reseting.
Tim H. :

Yeah, I wouldn't recommend that

Customer: Ok. Husband has panel open so he is closing it up and we are trying new batteries and firmly seated thermostat.
Customer: Is it correct to think a solid red light on control board is normal?
Tim H. :

It depends. On some, a solid light means the control is bad. I'd need a control model number. Or make and full model of furnace

Customer: Thermostat is flashing "cool on" fan is set to on. It clicks like it should engage but nothing.
Tim H. :

Turn the fan switch to on instead of auto. Does blower start?

Customer: It is in on position fan does not come on regardless of whether air is on.
Tim H. :

OK. The next step would be to check voltage at the thermostat wires to see if you have 24 volts

Customer: Carrier model CB5AXA048000AAAA. Control panel was replaced 6 months ago. No problem until 2 hours ago when I changed the batteries.
Customer: Pretty sure the solid red light means 24 volts. There is verbiage on the sticker to this effect.
Tim H. :

That will be your coil. That model doesn't help me

Customer: Sorry. Do you need to know from the unit outside.
Tim H. :

Nope, inside unit

Tim H. :

But not the coil ABOVE your furnace, rather the furnace itself

Tim H. :

You will most likely have to take a door off

Customer: I think I am going to try replacing the thermostat and see if that resolves the problem.
Tim H. :

Let's try something first...

Customer: Ok
Tim H. :

Turn furnace power off. Take thermostat off the wall. Find the red wire on R and the green wire on G. Take them off the screw terminals and twist together

Tim H. :

Then turn power back on

Tim H. :

Tell me if blower runs

Customer: Working.
Customer: Working on it
Tim H. :


Customer: Yes! It's blowing!
Tim H. :

OK, that would tend to tell me you have a bad thermostat

Customer: Good to know. So I shut off power, untwist wires and install new thermostat?
Tim H. :

Yes, The fact that blower runs tells me you have power and it is probably a thermostat issue.

Customer: Cool. Will replace now. Thank you very much.
Tim H. :

No problem. Be sure to label wires before taking off old thermostat. Thanks for using JA and please don't forget to rate my service. Post back with any additional ????'s

Customer: Absolutely. Thanks.
Tim H. :


Customer: Good night
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