Carrier Airconditioner 38QCA Heating problem

Hi Everyone,

I have a 3 phase Carrier 38QCA065 and have some issues with the Heat Cycle. the Cooling Cycle seems to work fine.

I turn HEAT 'on' the unit at thermostat, after 3 seconds, the relay clicks in on the panel, the compressor and fan unit starts for 5-8 seconds then stops. You can then hear a hiss noise comming from the pump unit.

It is quite cold here at the moment, but wanted to try the COOL cycle. After selecting COOL, the compressor and fan starts and continues to run (only tested for 3 mins and seem to cool fine).

After reading some of the general forums, could the 'reversing valve' be faulty?

Thanks for your help, Gary