Clean the evaporator and condensor coils first using appropriate cleaner made for this just like on a service truck, then change the return filter and report back with all pertinent information as follows. Measure the size of the return ductwork and note the filter size and efficiency rating / Airflow across evaporator coil taken using a pitot tube and traverse method in the supply duct at the proper location / Supply duct register temp / Ambient outside temp DB / Evaporator inlet WB / Low side pressure reading / Lowside line temp taken with a thermistor type probe at evap outlet / High side pressure reading / High side line temp taken at the condensor outlet with a thermistor type probe / Amp draw of compressor / Temperature of the compressor case at the bottom / Contactor voltage / Age and model number of the unit / Model of thermostat / Refrigerant type and complete history of any repair work that has been previously performed plus do a visual survey of all supply diffusers to be sure they are open and not obstructed same for returns. Now by golly we have a better than 50/50 chance of telling you exactly what is wrong with this unit.
you stated a guy came out last year for the smae problem. he put it to heat then to cool and it worked. now it wont work no matter what you do.you hear a click from the valve but no swoosh. unless you put a lot of freon in the system i dout this is freon related. the unit works fine in heat mode but wont through into cooling mode.
ok if i missed something sorry
you have one of sevaral things going on here and it is time to stop playing arround with this unit
the reversing valve is either defective or the coil is or you have crossed wirieng or the t stat is not working properly. or all of the above
put down you tools pick up the phone and call a tech
sit down on your deck or back yard and enjoy a beer while he go nuts fixing it. this will be cheaper in the long run
and safer for you heat pumps are tricky units to repair
is the unit cooling now did he put refrig.back into the system did he find anything else other than your service valve leaking
after reading everything in here i am not about to diagnose your system only try to lead you properly
no he just check the unit and found the leak at the service valve ,he'll be back friday to change the valve, but looking at the unit and see the lines sweating i,am not sould that the valve is the problem, would the servie valve stop the unit from cooling right ?