Bad thermostat ?


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Old 07-21-09, 11:00 AM
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Bad thermostat ?

My a/c unit on the 2nd floor did not kick on last night. I check the breakers, replaced the batteries in the thermostat and did a quick look for anything out of the ordinary, but didn't see anything. I didn't look at the electrical boxes outside next to the condensors yet. Not sure if what I would look for. I'll take a look later today hopefully.

I replaced the air filter the other day, but I don't see how that would affect anything. There's a switch on my thermostat where I can set the air handler to auto or on. I leave it at auto all the time, but when I switched it to on last night, the air handler didn't even kick on.

When the thermostat goes to "cool", I can hear it click and under normal conditions, the air handler and the a/c come on within seconds of that click.

The unit and thermostat is about 3 years old. It was a new install back then.

Any help would be appreciated.
Thanks,
Scott
 
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Old 07-21-09, 11:12 AM
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I would start by taking the t-stat off the wall and jumping out R+Y+G and see if the unit cmes on. If it does then it's the stat if it don't you need to check the low voltage for 24 volts.
 
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Old 07-21-09, 11:18 AM
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Thanks for the quick reply. I did see R, Y and G wires, but was hesitant to jump them. I had a similar problem with my heating where I had to jump wires to turn it on. In the end, it was a part that went bad.

Where does the 24 volts come into play ? Should I be looking for one of those boxes that converts AC current to 24 volts ? I know I have one of those for my heating system as I had to read up on that when I had that problem. If it's beyond my comfort level I won't touch it.

I guess thermostats can go bad after only 3 years ? It's a Hunter thermostat...I think it sells for around $30.

Thanks,
Scott
 
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Old 07-21-09, 11:28 AM
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R=24 V

Y= Cooling "outdoor unit"

G= Indoor blower

The transformer is located inside the airhandler.
 
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Old 07-21-09, 12:06 PM
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Great. Thanks for your help !
 
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Old 07-22-09, 07:03 AM
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Ok, I tried jumping the R, Y and G terminals with no luck. I tried the R to Y and R to G and nothing happened. I also have an identical thermostat for my 1st floor, so I swapped them just to see, but nothing happened. So I'm guessing I'll have to take a look at the transformer.

Is there something specific I should be looking for ? Do these things burn out or is it possible that a wire just got loose. I haven't touched anything on the air handler. I only poked my head up in the attic to see if I could see anything that looked weird.

Thanks,
Scott
 
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Old 07-22-09, 07:32 AM
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You'll need a multi-meter to confirm 120V to the primary side of the transformer and 24V on the secondary side. Before digging too far check your drain pan at the airhandler. There may be a high water cut-off switch that kills low voltage incase the condensate is clogged.
 
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Old 07-22-09, 11:13 AM
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Ok. Multi-meter to confirm power, check.

There are 2 pipes per air handler. One comes directly out of the air handler and one for the overflow pan. I thought it if the primary pipe was clogged, it would overflow into the pan and eventually to the outside. The drain pan is bone dry and looks like water never hit it.

I guess I will have to take off a couple of panels to look inside.

Thanks,
Scott
 
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Old 07-29-09, 11:53 AM
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Mattison,

Just wanted to check back in to Thanks you for your help on this one !!! After looking around the outside of the air handler, I ended up pulling the side panel off. I was surprised how easily it came off with just 4 screws. When I pulled the panel, everything inside looked as if it had never been used. It was a fuse that blew and it was nice to see that it was so easily accessible. So I replaced it and everything is back to normal.

On a different note, at the base of the coil or radiator looking thing, there is some rust. Is that normal or something I have to fix ?

Do you know how much it would have cost for a professional to come in and troubleshoot something like this ?

Thanks again,
Scott
 
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Old 07-29-09, 12:33 PM
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Glad to hear you figured it out.

The ruct on the bottom of the coil is pretty normal from the condensate running dowm.

A service call and repair would have run you $85 bucks or more. Probably more.
 
 

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