If the car is cool while is being driven and warm when stationary is most likely due to the cooling fan. Its cold when moving because air will passed through the condenser when you are driving, but when the car is stationary, the condenser depends on the cooling fan to release the heat.
Check the motor, see if its getting power, maybe you have a blown fuse, or if its good, then the motor itself is kaput.
The valve the other readers are referring to is the expansion valve. It's main function is to drop the refrigerant pressure & flow control. The cool refrigerant is passed through this valve on towards the coil where the pressure drops. Due to this loss of pressure, some liquid is changed to a low pressure gas. Its the remaining liquid that absorbs the heat on the coil. The car's blower blows air across this coil and into the car.
So if the valve is screwed, then it may not be regulating the refrigerant properly, which will mean it takes longer to cool the car. The car will eventually be cool but it takes time since the valve is not distributing enough refrigerant. Over time, the valve will completely stop working. Even if the service center say the electric clutch is bad, I would check the fuse first, it maybe be blown, that's why the clutch is not engaging. The compressor would be one of the last one to crap out.
Investigate thoroughly before spending money unnecessarily. My 2 cents. :wink: