I have a 2 years old house with builders YORK split airconditioner. ( two controllers, one upstairs one downstairs) 4 days ago, it stopped working. No matter what I do , but outside unit and attic unit did no respond at all (not even fan can be turn on).
I checked circuit breaker, it is not tipped. What's the problem could be?:confused:

Could be a blown fuse on a circuit board. Could be a defective low 24 volt transformer. If you have a zoned system it could also be a problem with the controller.

Best advice before you teak into it. Call a professional for on site service.

The reason I say this because it is much more complicated that just a single system and one wrong move can cause component damage and you will be buying some expensive parts.