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airheatman
airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 7773
Experience:  Furnace, A/C and heat pump specialist.
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My AC continues to run even after reaching set temperature.

Customer Question

My AC continues to run even after reaching set temperature.
JA: I'll do all I can to help. How long have you been dealing with this?
Customer: I have a thermostat on my middle floor and one upstairs both are cool than set temperature but the system continues to run and continues to cool. Been this way since turning on the ac about a month ago. I need to turn it off and on manually or will will just continue to run.
JA: Just to clarify, do you think this is a larger HVAC problem, or something specific to the thermostat?
Customer: I think it is the thermostat.
JA: Do you plan on doing the work yourself?
Customer: Batteries are good and no real batt indicator.
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the HVAC Technician about your situation and then connect you two.
Submitted: 4 months ago.
Category: HVAC
Expert:  airheatman replied 4 months ago.

Do you have two thermostats but only one system?

Customer: replied 4 months ago.
correct.
Expert:  airheatman replied 4 months ago.

OK now when you say unit continues to run, does both indoor fan and outdoor unit keep running?

Customer: replied 4 months ago.
it continues to cool further and further.
Expert:  airheatman replied 4 months ago.

OK now usually with two thermostats, one is main thermostat or master and second one is a zone control or slave.Do you know which is main?

Customer: replied 4 months ago.
the middle floor is the master.
Expert:  airheatman replied 4 months ago.

OK now when you say you have to turn off manually.Do you mean with system switch at thermostat or breaker at unit?

Customer: replied 4 months ago.
System switch at thermostat.
Expert:  airheatman replied 4 months ago.

This points to a thermostat sensor issue.Is it the middle one that you have to shut to off?

Customer: replied 4 months ago.
I shut off at the middle level thermostat to control temp or it will continue to run and cool indefitely.
Expert:  airheatman replied 4 months ago.

Sounds like the temp sensor is not working .What is model on thermostat.I will see if there is any calibration we might try

Customer: replied 4 months ago.
I do not see anything stating model number but it is the Honeywell Chronotherm III.
Expert:  airheatman replied 4 months ago.

Let me see if I can find anything on calibration

Expert:  airheatman replied 4 months ago.

Do not see anything that is adjustable as far as the sensor.I would start by replacing batteries and if that doesn't help. look into replacing this thermostat.

Customer: replied 4 months ago.
Ok. That's what I figured.
Expert:  airheatman replied 4 months ago.

If you have further questions, please let me know.

Thanks for letting me work with you.If my answer has been polite, professional,and thorough, please click one of the ratings before you go. If you still need help let me know!.Expert is not paid for assisting you until you rate answer.Feel free to follow up for 30 days at no additional cost. Bonus always appreciated if you feel justified.