My A/C turns off and on at seemingly random times. When it is on it's cold. According to my mechanic, my car has been very well maintained and the engine is in great shape, but they mentioned the following possible issues with the A/C:
I'm not sure what the actual problem is, though, and I'm wondering how to start troubleshooting.
(Unrelated: The mechanic also said the motor mounts may need to be replaced but I'm not sure what to do about that.)
Repairing almost anything on an AC system requires the system to be refilled with coolant, and the procedure costs about $140 for most vehicles (this is completely different from topping up a system that is still sealed). This needs to be added to whatever the actual repair cost is.
As for your motor mounts, they do tend to go bad with time and mileage. Is there any chance you can pop the hood and take pictures for us? Motor mounts and big honking things attached to your engine and the car. There's usually 4 of them, look in front, behind, left and right. Replacing these can be fairly substancial.
While I cannot speak for the intent of the mechanic, or the costs incurred (every vehicle is different) I can answer some points in your questions.
Replacing the schrader valves will require a system vacuum and recharge as if the schrader valves leak, the freon has escaped and has likely normalized with atmospheric air. This means that the system has become contaminated and will need to be flushed, vacuum drawn, and refilled. It is a very time consuming process, especially if other leaks are present, which can be found once a vacuum is drawn on the system.
As for the motor mounts, It depends on the mileage of your vehicle. Some vehicles are prone to premature motor mount failure. If your vehicle leaks, or has not been maintained regularly, this can also contribute to mount failure. Replacing all of the motor mounts should not normally be necessary, however I've run into cases where literally every motor mount had to be replaced, and that in itself is not an easy feat. The motor must be supported, and some mounts may be in difficult portions of the engine bay and may not be easy to get to.
You should always go get a second opinion. Do not take one mechanic's word for it, especially if you feel or suspect he's giving you a run for your money.
More than likely you have leaking o-rings on the AC springlock connectors.
Discharge system, Replace all o-rings on all spring lock AC connections, be sure to Not score the soft aluminum when removing old o-rings. Lincoln specified thicker o-rings under a TSB (Technical Service Bulletin), so get the improved o-rings from Ford. Clean spring lock coupling connectors and o-ring grooves with maroon colored 3M Scotch Brite (cut in strips) before installing new o-rings. Re-charge system.
