AC not shutting off

[brehmdan]

Hello,

I have a Nordyne MGHA-070ABFC-05 (serial: MGH9510-04280) which is a split unit (AC and heat in one unit). We installed a new t-stat (Honeywell programmable) thinking that was the issue but am still having the same issue. The old t-stat was a mercury style w/a heat/off/cool selection.

Issue is when we set the t-stat to a certain temp, the AC continues to run even after it reaches the designated temp. I found that I have to manually operate the t-stat in order to turn on/off the AC. I found the only way to turn off the AC is to turn the t-stat to 'heat', or to switch off the breaker power supply to the unit. (Even when I switch the t-stat to 'off', it still continues to run. The AC continuously runs cold air even after it reaches the temp selected.

Any ideas what could be causing this?

Oh, there are only 2 wires that run to the t-stat (white and red). We tried hooking them up different ways on the t-stat but we either run into the same issue where you have to switch it to heat to turn off, or it continues to run until we flip the breaker.

The furnace runs fine!

[Robert]

Hi,


You have a 2 wire set up. Wall t-stat should remain in HEAT selection year round.


Then, the two switches at furnace should be set to the season, HEAT for winter and COOL for summer and fan switch to AUTO always.



Otherwise, you will need to replace 2 wire control box with a 5 wire box and run 5 wire t-stat wire to t-stat which will need to be a 5 wire t-stat for your furnace and a/c system.


During summer, a t-stat reversing relay in the a/c control box controls the a/c system.


With switches set as stated, set temp where it is wanted and system should turn itself off and on as desired.



Thanks,
Robert

[brehmdan]

I'll try those options when I get home! Hopefully it's the easier of the two!

Thanks Robert! I really appreciate your help!

[Robert]

You're very welcome, happy to help. IF everything is operational, it works well.




Thanks,
Robert