My heat pump will not come on in HEAT or A/C. I thought I might have a simple defrost control board problem, but still no go after replacing the board and the defrost relay. I checked the pressure switch and it is not tripped. I've checked all the circuit breakers and they, too, are all set. I've checked the outside unit using the "test" switch inside on the start relay and the unit will come on, but won't stay running on it's own. When I select HEAT, I wait the necessary five minutes for the unit to switch and it keeps switching to AUX HEAT. In A/C the unit does nothing

Hi; Need more info. How old is the equipment,look on the outside unit data plate it will give the built date usually in the top right corner. Also heat pumps can run with a faulty defrost board. I would check for control voltage at the secondary side of the transformer should be atleast 24 volts ac. Also the test post on the defrost board are for troubleshooting a defrost problem not an operational problem.When the posts are temporarely shorted the condensor will go into a defrost cycle This step will let the tech. know if defrost is operating normally. Also I have seen a reset switch manualy reset but not reinergize the control voltage. Also the outdoor unit has a delay timer that will wait for freon press. to equalize befor letting the unit operate. One more thing do You now if Your tstat is operating normally. One more idea is the defrost sensor if faulty it can leave the condensor in a defrost state of operation. This intern will sometimes go to heat strips because they are used in the defrost cycle to warm up the air conditioning going on durring a defrost cycle. One more thought is does the control contactor have 24 to 27 volts going to it if so replace the contactor. To test this using a voltage meter and touch after waiting 5 min. both sides of the coil. Remember voltage is deadly so ..When in doubt call a qualified tech.I ASSUME NO LIABILITY FOR INJURIES TO YOU OR THE EQUIPMENT BE CAREFULL!!! IF YOU GROUND YOURSELF BETWEEN 230VOLTS THIS BE VERY BAD...alpharome416