[JA]

Hi Bojan,

If the heating function works well, but the cooling not at all then depending on the design you may have a faulty reversing valve, valve wiring or perhaps there is no voltage to the valve when there should be, i.e: wiring fault to the valve. Typically there should be 24VAC when the valve is energized and nothing when relaxed. One way it sets cooling the other way heating . I dont know if that 24VAC is supplied via a relay to the reversing valve, but if it is then also check the function of the relay. Of course if there is a fault in the temp sensing /thermostat circuitry then that too could cause a non-start on cooling, if the unit thinks it's already cold enough and would also explain it being able to start on heating. (Also check continuity to the in room thermostat / wiring)

EDIT: I just noticed your picture appears to be for an in wall box unit, my comments about the thermostat were more centered around a larger split system, with remote thermostat so YMMV with an all in one, but the principle remains

It goes without saying, that checking such would mean working with live equipment, so , to anyone, irrespective of experience, attempting such, I'd say be careful and do not attempt if in doubt.

Best
JA