If you remember, that was my question whether the AC trips at idle or not. Now what the mechanic did, will not solve the problem. The original temperature sensor inside the evaporator (the cooling coil inside dash unit) will trip the AC at about 7-8 degree cool air. Your AC system is not able to cool the air to 7-8 degree thats why it does not trip on idling.
The thermostat he installed is actually a general purpose thermostat whose trip temperature is adjustable so he set it to trip at whatever temperature your AC air is at.
This will not solve your issue and neither a Terios kid compressor. The air conditioning system is designed according to laws of thermodynamics and every component is well calculated.
Since every mechanic is saying different thing, so I am pretty sure none of those has actually diagnosed the problem. If you still want to spend money to fix this AC, I will suggest you to try and find the brand new genuine Cultus compressor, the expansion valve and the filter (AKA bottle).