My AC isn't blowing cool air. Trying to troubleshoot. The thermostat's temp gauge has not been working properly for some time - BUT the AC has been coming on fine up until today.

Possible the switch is bad? If so, anyone know how to check it?

Best I can read from online sources there's a 30VAC supply involved. Several wiring contacts exposed underneath the cover. I can measure 5.3VAC from ground to all 3 contacts. Still no idea if switch is making contact in the "cool" position.

 

Should be reading off of R to C or ground. You can test by jumping R, Y and G together, if the system starts, then it may be the t-stat.

Voltage is about 24 volts.

The stat you have is a basic switch stat,

 

Thanks,

Can this be done without removing the 2nd cover?

With 1st cover removed I see 4 screw connections - none labeled.

1) upper left - white wire that runs to lower right screw

2) lower left - blue wire that runs to bulb

3) lower right - tan wire that runs end of bulb, plu white from up left

4) upper right - no outside visible connection

Also yellow wire running from end of bulb to thermostat assembly.

Hopefully worst case mistake would be shorting to ground but just want to make sure.


EDIT:

Got a warning sticker on there that reads:

"Do not short out terminals on gas valve or primary control to test. Short will burn out heat anticipator."

Don't know if this qualifies as test condition from above.

Worse. The genius who designed the front of the 2nd cover left a slit too small for a proper sized screwdriver to get in and turn the screw to take the cover off without breaking the plastic. Seems impossible. There's a guy on Youtube with the same model thermostat as mine who makes removing the cover look easy as pie. Of course it should be. I guess his didn't have the narrow slot.

 

I've never been around these white rodger t-stat, there should a couple of screws or something to remove the base from the sub-base.

Take a reading at the furnace then.

 

Ok. Managed to get the cover off and with the system selector in the "Off" position I get 28VAC from RC to Ground.

Does that clear the t-stat?

 

No, if you are getting full power, then it could be the stat.

Add a jumper between R, Y, and G. A/C should run along with the fan. If everything stays running the whole time, then it's time for a new stat.

 

Ok so no danger in doing what the warning sticker says?

"Do not short out terminals on gas valve or primary control to test. Short will burn out heat anticipator."


Sorry for being overcautious but it'd be just my luck to run into the odd exception case.

Sticker referring to something totally different?

 

Yes, it's something else.

Jumping R-Y-G is what the t-stat use to turn on cooling.

 

I jumpered the connections. Air comes on. Should the compressor turn on with this connection? The compressor is not making any sound.

Air that comes out doesn't feel very cool.

 

Yes, the compressor should of came on.. Y is for compressor.

Some compressor has a 5 minute time delay, may let it be for longer than 5 min to see if it does come on.. If it don't, make sure Y wire from the wall is in place.