Air Conditioning - Intermittent A/C shutdown

Hi, I have a York gas furnace and A/C evaporator coil in the house and an outside A/C compressor. Over the winter, the gas heat would intermittently not work while the fan still ran. Now that it's hot, the A/C is intermittently not working while the fan will still run. The outside compressor also shuts off when the A/C stops working inside. The house fan will still run though blowing room temperature air. We called in a technician who replaced the thermostat with a new Honeywell model for $135 and added 2 lbs of coolant to the outside compressor at a charge of $250. It fixed the problem for a week, and then yesterday it stopped working again only to start working again today. What could cause these intermittent failures? Also, were these charges reasonable? They seem too high. Thanks for any help you folks can offer.

Did the tech locate and repair a leak?

The stat may have been bad no way to tell from here, the unit could be locking out on low pressure, the compressor could be heating up and tripping on thermal, both could be caused by a low refrigerant charge. Which is why I asked about the leak repair.

The prices don't seem high to me, normal for my area. Call them back to look at it again, talk to there service manager.

A reputable company will honor there work.