HVAC not working after battery died in thermostat

Reply

  #1  
Old 10-14-20, 04:37 PM
N
Member
Thread Starter
Join Date: Jan 2008
Location: NoVA
Posts: 205
Received 1 Vote on 1 Post
HVAC not working after battery died in thermostat

Earlier today I noticed the display on my thermostat was blank, knowing it takes batteries i opened the battery door to find one battery had leaked. I cleaned the contacts as best I could, installed fresh batteries and assumed that would be it.

After a few minutes I noticed the unit not coming on, I know it can take a few minutes to restart, but it has been 15 or so. Temperature reads 78F cooling set to 72F, it clicks but nothing comes on in any mode.... fan on or auto, cool or heat. It initially flashes "Cool On" or "Heat On" then that remains steady but that's all.

The unit was working fine this morning, heating as expected. I pulled the thermostat off the wall and all the wires appear securely in place. I checked the indoor unit and it's getting power, I haven't measured it, but can feel the hum from the power.

Are there any tests I can do on the indoor or outdoor unit to confirm they are working correctly? I've replaced capacitors on the outdoor unit, so am comfortable working around the unit as kind as I know what I'm looking for. I'm not comfortable randomly poking around.

What's funny, I was just talking to my wife a few days ago about replacing the thermostat with a new programmable unit and then this one decides to cause issues. I'm going it's just the thermostat, but I don't think I'll be that lucky.

Thanks.
 
  #2  
Old 10-14-20, 05:02 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 60,874
Received 1,342 Votes on 1,240 Posts
If you have a battery thermostat..... it works solely by battery.
In other words..... if the thermostat is dead....it's bad. The system won't respond.
Either the acid leaked into the stat or the battery contacts are corroded yet.

Just re-read your post. The thermostat appears to be working but nothing is happening.
Do you have a heat pump system or a gas furnace or ??
 
  #3  
Old 10-14-20, 05:14 PM
N
Member
Thread Starter
Join Date: Jan 2008
Location: NoVA
Posts: 205
Received 1 Vote on 1 Post
It's a heat pump, Trane XR13.

I did wonder if battery acid leaked into the thermostat, but the thermostat does appear to be working, in that pressing the buttons on the thermostat do what they should and it makes clicking sounds. Still doesn't rule it out entirely.

I'm weighing up installing a new thermostat and hoping that fixes it. A call out to a tech will likely run $100 minimum. If possible I'd like to determine if everything else is functioning first though.
 
  #4  
Old 10-14-20, 05:18 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 60,874
Received 1,342 Votes on 1,240 Posts
Take the thermostat off the wall. Snap and post a picture of the wiring for me.
I'll tell you what to do.
How-to-insert-pictures.
 
  #5  
Old 10-14-20, 05:40 PM
N
Member
Thread Starter
Join Date: Jan 2008
Location: NoVA
Posts: 205
Received 1 Vote on 1 Post

Hopefully, that works.
 
  #6  
Old 10-14-20, 05:47 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 60,874
Received 1,342 Votes on 1,240 Posts
Nice picture. I just cropped it a bit.

Take a piece of wire. Can be anything. Single conductor. Telephone wire. Bare wire.
Jump from the red (R) terminal to the the green (G) terminal.
The blower should start running.

You have a C wire connected to your thermostat. That means it should work without batteries.
 
  #7  
Old 10-14-20, 05:55 PM
N
Member
Thread Starter
Join Date: Jan 2008
Location: NoVA
Posts: 205
Received 1 Vote on 1 Post
Thank you... so, tried that and nothing, tried at the screw, at the wire and where the thermostat plugs in. Same result with all, nothing happening.
 
  #8  
Old 10-14-20, 05:57 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 60,874
Received 1,342 Votes on 1,240 Posts
Do you have a meter ?
Set it to read 24vAC.
Check from R to C ...... should be 24vAC.
If not.... there is a problem at the air handler. Possible blown fuse or transformer failure.

I don't think the batteries had anything to do with this failure.
 
  #9  
Old 10-14-20, 06:05 PM
N
Member
Thread Starter
Join Date: Jan 2008
Location: NoVA
Posts: 205
Received 1 Vote on 1 Post
Set the meter to 200 Vac, not reading anything between those terminals.

Now knowing that the thermostat should work with that C wire, I assume the batteries were long dead and whatever failed caused the thermostat to then show blank due to the batteries being dead, but more importantly there being no power to it either.

Is checking the fuse or transformer at the site handler straight forward?

edit: tried to attach a picture but it keeps failing at 50%... I took the panel off, after shutting off power. I see 2 breakers to the left above the blower motor. Then a panel to the right with a bunch of warnings, and finally a panel with wiring diagram on the front, not sure if the fuse is behind there.

Edit 2: found the fuse and its clearly blown. Now, replacing it is easy, but if it pops again then id assume there's a bigger issue somewhere.

Looks like I won't get it sorted tonight, 5A fuse in there and the smallest I have is a 10A.
 

Last edited by naiku; 10-14-20 at 06:35 PM.
  #10  
Old 10-14-20, 06:44 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 60,874
Received 1,342 Votes on 1,240 Posts
Yes.... you don't want to exceed 5A. I usually use a 4A.
Your pictures may be too big.

What mode was the system in..... heat ? I'm assuming yes.
A defective contactor in the outside condenser.
Shorted thermostat cable from house to outside condenser.
Defective reversing valve coil in Rheem or Ruud brand condenser.



 
  #11  
Old 10-14-20, 07:49 PM
N
Member
Thread Starter
Join Date: Jan 2008
Location: NoVA
Posts: 205
Received 1 Vote on 1 Post
Ran into town and grabbed a pack of 5A fuses, everything working currently in cooling mode.

It was in heat mode earlier, I'll likely need heat again tomorrow. If it blows the fuse I'll be back here asking for advice on checking those things!

Thanks again for the help, much appreciated.
 
  #12  
Old 10-14-20, 07:53 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 60,874
Received 1,342 Votes on 1,240 Posts
What brand is the system ?

I work days and am here at night. There are others that can help.
 
  #13  
Old 10-14-20, 08:15 PM
N
Member
Thread Starter
Join Date: Jan 2008
Location: NoVA
Posts: 205
Received 1 Vote on 1 Post
It's a Trane XR13, about 11 / 12 years old.

Looks like the contactor and reversing valve coil would both be fairly straightforward to check and replace if needed. A shorted thermostat cable maybe not quite as easy.

Still, cooling beautifully at the moment and we'll see when I need the heat!
 
  #14  
Old 10-14-20, 08:23 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 60,874
Received 1,342 Votes on 1,240 Posts
In order to cool..... 24v is applied to the reversing valve. So in heat mode the reversing valve is not powered. That removes one problem item.

That leaves the wiring and the contactor. They would be the same for heat and cool.
The only other differences when the system is heating is if it goes into defrost and then you have problems.

Contactor coil failing and outside wiring issue are the two biggest culprits.
Usually the outside cable would be chewed by an animal or hit by the weedwacker.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: