A/C Thermostat question.

[Frankie]

Our home thermostat quit displaying LCD last night and sure enough our cooling system does not work. We bought a new thermostat (4-wire system) and connected it. But still things are not working.

Before I call the pros tomorrow, only to find out I have overlooked something stupid, I want to know if it could be a faulty circuit breaker. All breakers are in the on position. The A/C breaker of course is a 220. Does this also handle the little bitty thermostat and the little current it needs?

Could there be other causes?

[Brock]

Do it have batteries in it?

[Bugeater]

The thermostat runs off of a 24V transformer. If you have a multimeter, set it to DC and see if you have 24V across the red and white terminals.

[Bugeater]

The AC breaker is only for the outside unit, it's not connected to the thermostat in any way. There's also a fuse disconnect switch somewhere, it's usually mounted near the furnace somewhere. That's where the power for your thermostat comes from.

[Bugeater]

Or it may need batteries...lol.

[Frankie]

Do it have batteries in it?

Yep. But the old one did not. (Both non-programmable)

[Frankie]

The AC breaker is only for the outside unit, it's not connected to the thermostat in any way. There's also a fuse disconnect switch somewhere, it's usually mounted near the furnace somewhere. That's where the power for your thermostat comes from.

The thermostat runs off of a 24V transformer. If you have a multimeter, set it to DC and see if you have 24V across the red and white terminals.

I didn't think it ran off of a 220 breaker. This confirms it. I'll go look for that 24V trany.

[Bugeater]

There's usually another circuit breaker in an electrical box on the outside of the house near the AC unit.

Are you getting a readout on your thermostat at all?

[Frankie]

There's usually another circuit breaker in an electrical box on the outside of the house near the AC unit.

Are you getting a readout on your thermostat at all?

Looks like I have misplaced the tester the last time I used it. :banghead:

It's hot in here. Not yet Angelina Jolie hot, only Hope Solo hot!

Here's a picture of the transformer I think you are talking about. But I didn't find a switch near the furnace. At least nothing seemed like it should be it.

[Bugeater]

Are you getting any display at all on your thermostat?

[Frankie]

Are you getting any display at all on your thermostat?

The new one has a regular thermometer type. No LCD. It's stuck around 90. I don't understand the 2 AA batteries we had to put in this thing.

[Bugeater]

The new one has a regular thermometer type. No LCD. It's stuck around 90. I don't understand the 2 AA batteries we had to put in this thing.
Yeah, that's weird. I thought they all had digital displays these days. Switch it from "Auto" to "Fan On" and see if your fan starts running.

[Frankie]

Yeah, that's weird. I thought they all had digital displays these days. Switch it from "Auto" to "Fan On" and see if your fan starts running.

I did. It didn't. :(

[Brock]

The new one has a regular thermometer type. No LCD. It's stuck around 90. I don't understand the 2 AA batteries we had to put in this thing.

I believe the batteries actually power the display. That's why I'm very curious as to why your display isn't working if you put new batteries in it.

[Bugeater]

I did. It didn't. :(
What happened anyway, was the system working fine and then up and suddenly quit on you?

[Frankie]

I believe the batteries actually power the display. That's why I'm very curious as to why your display isn't working if you put new batteries in it.

The old thermostat with the LCD display did not have batteries! It's probably supposed to get power from the wires coming out of the wall.

[Bugeater]

And your new one requires batteries, but doesn't have a digital display? That doesn't make any sense at all.

[Frankie]

What happened anyway, was the system working fine and then up and suddenly quit on you?

At first we didn't even notice that it was not working. We first noticed the lack of thermostat display. Then we realized the system wasn't working either.

[Brock]

The old thermostat with the LCD display did not have batteries! It's probably supposed to get power from the wires coming out of the wall.

I can honestly say I've never seen one like that.

[Frankie]

And your new one requires batteries, but doesn't have a digital display? That doesn't make any sense at all.

Join the club. I've been trying to convince my panicky wife about that too.

I even took the batteries out thinking maybe it's interfering with the power supply. But nothing happened either. the booklet does not say why the batteries are needed. Just says that we should put two AAs in!

[Bugeater]

I have no idea if my digital one has batteries or not. It's been there for 10 years and I don't recall ever changing them.

[Brock]

post a pic of your old thermostat

[Brock]

Oh, and I think that transformer you posted a pic of is your doorbell transformer.

[Bugeater]

Anyway, it sounds like you've lost power to your system. It's possible the fuse in the disconnect switch blew for some reason. Somewhere on the side of your furnace should be some flex conduit coming out, and it should go to a junction box with what appears to be a light switch and a square metal door that covers a Buss type fuse.

[Bugeater]

Oh, and I think that transformer you posted a pic of is your doorbell transformer.
I was thinking telephone...lol

[Frankie]

I can honestly say I've never seen one like that.

Here it is:

[Frankie]

Oh, and I think that transformer you posted a pic of is your doorbell transformer.

That could be. I have to go look for the thermostat one now I guess.:redface:

[Bugeater]

That could be. I have to go look for the thermostat one now I guess.:redface:
It's going to be inside your furnace somewhere, but without some type of meter, finding it will be useless.

[Frankie]

Anyway, it sounds like you've lost power to your system. It's possible the fuse in the disconnect switch blew for some reason. Somewhere on the side of your furnace should be some flex conduit coming out, and it should go to a junction box with what appears to be a light switch and a square metal door that covers a Buss type fuse.

That's what I have concluded too. Now I have to go try to find the other stuff you are telling me. I might come back and post yet tonight. But don't stay up on my account.

[Frankie]

It's going to be inside your furnace somewhere, but without some type of meter, finding it will be useless.

I think I know were I have the meter. With a friend I think. Tomorrow I'll have one one way or another.

[Bugeater]

That's what I have concluded too. Now I have to go try to find the other stuff you are telling me. I might come back and post yet tonight. But don't stay up on my account.I'll be up for a while. Look for something that looks like this:

http://z.about.com/d/electrical/1/0/X/3/-/-/fused-disconnect-switch-170.jpg

[Frankie]

post a pic of your old thermostat

If I can retrieve it from trash. Fariba is the fastest trasher in the West.

[Brock]

Mine just looks like a regular old light switch on the wall beside the furnace.

[Bugeater]

Mine just looks like a regular old light switch on the wall beside the furnace.
Yours isn't fused?

[Brock]

Yours isn't fused?

Don't see one. There's the 110 wire coming from the breaker box going into a switch box and a wire from there going into the furnace box.

[Bugeater]

Don't see one. There's the 110 wire coming from the breaker box going into a switch box and a wire from there going into the furnace box.
Huh, the local gas company here won't approve a furnace installation without one.

[Frankie]

I'll be up for a while. Look for something that looks like this:

http://z.about.com/d/electrical/1/0/X/3/-/-/fused-disconnect-switch-170.jpg

I think this is it.

[Frankie]

post a pic of your old thermostat

Got it out of the trash can. FWIW it may be perfectly OK.

[Brock]

Got it out of the trash can. FWIW it may be perfectly OK.

And that did NOT have batteries? Welp, I'm stumped.

[Frankie]

And that did NOT have batteries? Welp, I'm stumped.

:D It did not. Obviously it got it's power for the display from the little wires.

[Bugeater]

I think this is it.
Yeah, that's it. I don't suppose you have an extra fuse laying around that you could try in it?

[Frankie]

Yeah, that's it. I don't suppose you have an extra fuse laying around that you could try in it?

That would have to be tomorrow. I suppose the fuse sits in that round housing and it snaps open. Correct?

[Bugeater]

Well my curiosity got the best of me and I went and checked my thermostat, and it does have three AA batts in it. I'm tempted to start digging through my notes from school but I don't believe the thermostat is Frankie's problem.

[Phobia]

You may be able to bill Frankie more over the internet than you could if you were at his house, Bugeater.

[Bugeater]

That would have to be tomorrow. I suppose the fuse sits in that round housing and it snaps open. Correct?
Yep, and the fuse just threads in like a light bulb. I'm not 100% convinced that is the problem anyway, but without getting some electrical readings it's really hard to say for sure what's going on. Sucks too, it's a muggy SOB out there tonight.

[Bugeater]

You may be able to bill Frankie more over the internet than you could if you were at his house, Bugeater.
Shit if he lived close by I'd go check it for nothing, I need the troubleshooting practice.

[Frankie]

Well my curiosity got the best of me and I went and checked my thermostat, and it does have three AA batts in it. I'm tempted to start digging through my notes from school but I don't believe the thermostat is Frankie's problem.

That's why I have pulled the old one out of trash.

[Frankie]

You may be able to bill Frankie more over the internet than you could if you were at his house, Bugeater.

Go to bed Phil.

[Frankie]

Yep, and the fuse just threads in like a light bulb. I'm not 100% convinced that is the problem anyway, but without getting some electrical readings it's really hard to say for sure what's going on. Sucks too, it's a muggy SOB out there tonight.

Yes it is. I'll set up a fan for tonight. "After all, tomorrow is another day."

Goodnight for now. Thanks for the help. I'll let you know what happens tomorrow.

[Frankie]

Shit if he lived close by I'd go check it for nothing, I need the troubleshooting practice.

Omaha's close to central Iowa. :shrug:

;)

[Phobia]

Go to bed Phil.

Open your wallet, cheapskate.

[Frankie]

Open your wallet, cheapskate.

That's what the IRS is telling me these days. :(

[Chief Roundup]

Okay sounds like a transformer or a fan control center probably went bad if you have checked the breakers. You should have seperate breakers for your A/H (Air Handler), or Furnace and your A/C or Heat Pump unit.
If you only have a 4 wire set up you probably have a gas furnace with straight A/C.
If this is the case you will have a 110/120 breaker for the furnace and a 220 breaker for the A/C, outdoor, unit.
If you have no fan when you turn the switch to "fan on" then you are not getting a signal from the stat to the furnace.
Check that breaker for the furnace. Yes sometimes depends on code and install date but if it is a furnace then there might be an outlet close to the furnace that you should check as well. If it is a heat pump Air Handler (220) then there should also be breakers or fuses inside the Air Handler.
Now if your condensate drain has a condensate pump in use there should be a safety switch wired in that will also kill the unit so that it doesn't flood your basement attic or crawl space if the installers couldn't get enough fall to get the condensate drain outside of the house or if it is having to be pumped out it could be clogged up.
Batteries are used as a backup in case you lose power or if you do not have a common wire to the thermostat from the furnace or air handler.

That pic that you put up doesn't look right. There should be more wires running to and from it than just those 2 wires. I tend to agree that is probably the transformer for your doorbell. The transformer will have thermostat wires that go from the Furnace or Air Handler to the thermostat on your wall and that go to your outdoor unit.

[Bugeater]

Actually, I have a transformer similar to that near my furnace that I believe powers my humidistat.

[Chief Roundup]

<iframe width="425" height="349" src="http://www.youtube.com/embed/_HyhUyU-AMI" frameborder="0" allowfullscreen></iframe>

As I don't know how to post regular pictures this video shows you a few different styles of transformers used in HVAC.

[Baby Lee]

Check your air filter. Forgot all about mine and it clogged so much that the fan couldn't push air. Thus the condensor didn't turn on as the fluid in the radiator was alread cold.

[Lzen]

Check your air filter. Forgot all about mine and it clogged so much that the fan couldn't push air. Thus the condensor didn't turn on as the fluid in the radiator was alread cold.

Wow. You must have not changed the filter for months.

[LOCOChief]

Our home thermostat quit displaying LCD last night and sure enough our cooling system does not work. We bought a new thermostat (4-wire system) and connected it. But still things are not working.

Before I call the pros tomorrow, only to find out I have overlooked something stupid, I want to know if it could be a faulty circuit breaker. All breakers are in the on position. The A/C breaker of course is a 220. Does this also handle the little bitty thermostat and the little current it needs?

Could there be other causes?

There in fact could be other causes:

Question: Do you have natural gas appliances such as stove and/ or oven?

If so make sure all windows and doors are closed, turn on the gas without igniting, wait an hour or so then enjoy a cigar.

Hope this helps.

[Frankie]

LADIES AND GENTLEMEN

VICTORY IS OURS!!!


It WAS the fuse. I had no idea how this thing was fused and learned something from the process. Thank you all for helping. The late night contributors to this rescue will all get a rep. :)

[Lzen]

LADIES AND GENTLEMEN

VICTORY IS OURS!!!


It WAS the fuse. I had no idea how this thing was fused and learned something from the process. Thank you all for helping. The late night contributors to this rescue will all get a rep. :)

Well, at least it wasn't a big deal. But I'm surprised anything like that nowadays has a fuse. I thought every modern thing used a breaker.