Can anybody recommend an air conditioning service in the Darkside area with good equipment and quality work? 

A friend who has a large expensive house with many aircon units to service recommended Niran Air. I gave them a try and they did a thorough job on my 3 units and I recall the price was B400 each. They sent a 3-man crew (not the usual 2). The head man, Niran, speaks decent English so communication is good. He picked-up the English while working for a year at the tech company Cisco in Texas. His number: 084-462-9307.

I personally always consult with some reliable repair services when buying serious equipment.

Numchai on sukhumvit rd did ours ,ist class service ,and not expensive ,i always use them .