I have a Lennox ELITE series XP16-24-230-04 heat pump, CBX27UH-030-230-6-02 Air Handler and a Honeywell Vision PRO TH8000 thermostat.
The problem is that at various time the units will go into a heat mode (uncontrolled) when the thermstat is set for cooling.
I have been able (sometimes) to get back to into a cooling mode by operation of the circuit breaker thus probably reseting the units. At present this operation has not been successful.
Can you provide me some guidance?
Next time it happens use your meter and check between o and c at the heat pump. There should be 24 v there with a cooling call. If that's good the check between w and c at the air handler and at the heat pump to see where the heating call is coming from.