It is a RobertShaw 9600-

Setting is for MANUAL

Temperature in house is 76 degrees

Manual setting for a/c to come on is 79 degrees.

A/C comes on. A/C installer told us thermostat unit is BAD. Sold us a replacement.

Same issue.

Per RobertShaw help desk " this is a wiring issue"

Question: What wires could be involved?

Thanks

Montaques

You need to check all the low voltage wires from the stat to the airhandler. If the unit is not shutting off, sounds like the wires from R (normally red) and Y (normally yellow) are making contact