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BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22510
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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I have a Honeywell digital thermostat. Digital readout is

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I have a Honeywell digital thermostat. Digital readout is only partially showing, a/c not operating with fan in "Auto" position, only if switch is in "On" position. I don't want to force it "On" if there is a larger issue. I have replaced the batteries in the thermostat and readout remained the same. I have a 4-ton forced air unit. Only 11 months old. Any help would be greatly appreciated. Thanks!

Does the thermostat say AC-

Customer: replied 3 years ago.

Since sending the question I've noticed that the display shows the "Inside" temperature but does not show a "Set To" temperature on the Cool setting, only on the Heat setting. So display simply reads "Inside 88". Its a Honeywell TH3210D1004.

Thank you,

Do you mind setting to cool...and then pressing the down button to activate ac....and tell me if you hear a click at thermostat or if the outdoor ac unit comes on?

Customer: replied 3 years ago.

OK. No click at the thermostat (the display does light up), and the outside unit is not running. Note the thermostat is on the "Auto" setting. In the "On" setting it turns on the blower but again the outside unit does not come on.

Thank you.

Do you mind a bit more invasive procedure?

It involves removing the top section of thermostat.

Customer: replied 3 years ago.

Just pop it off the base on the wall? No problem. What do you need me to look at?

We need to look at the terminals where the wires attach....then locate terminals R and Y..

use a paper clip shaped in a U...touch one end to R and the other to Y and hold.

Tell me if outdoor unit kicks on.

Customer: replied 3 years ago.

Yes, outdoor unit kicked right on.

Thank you.

This means the either the display logic or the delay timer in the thermostat is likely defective.

We just bypassed the thermostat and sent signal direct.

I am afraid you will need to replace the thermostat.


Customer: replied 3 years ago.

Wow. Even though the house was just built 11 months ago and it's all brand new? Would a defective unit explain why I can change the temperature in the "Heat" setting but not even get a "Set To" option in the "Cool" setting?

That is correct.

I wish had better info as to why...but I simply go by process of elimination. And at this point eliminating the thermostat starts the unit..


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Customer: replied 3 years ago.

Well I'll give it a shot. Hope it's a Lowes unit given that it's a Saturday night. If she keeps giving me trouble I'll give you a shout. Thanks for the help!