We have two 3 ton envision 2 units on a closed loop system installed in 2012. Never had any issues. Both units are in cool mode. Came back from an errand and the downstairs unit was blowing warm air while in cool mode. No lights indicating a problem. Turning the thermostat to off will not shut off the system, killed power to the unit and the started it back up and it's doing the same thing, blowing heat. It appears to be stuck in heat mode regardless of what you put the thermostat on. The only way to stop it from running is to kill the breaker. Not sure what I can do at this point other than call a tech. Any thoughts? Thanks

At times, the fan may want to continue to run for 5 minutes after you shut off at T-Stat. It sounds like your reversing valve may be stuck. Try cycling back and forth between heating and cooling a couple times. Wait at least 5 minutes between cycles.

You may want to try tapping on either end of the reversing valve with a softer item like wood or plastic screwdriver handle.

If you have the 10 year warranty (or not), call a tech. The installer seems competent if you have gone 3-4 years without a problem.