Amana ptac ac turn on runs short time on cool and go to fan mode warm air.

If this unit has the old style control with the knob instead of the digital control panel
then I would suspect this first. This is the first component to fail on these units. I have
replaced two already and the kit has good instructions and all components.
Takes approximately an hour to do and mount the new sensors. (The transformer is
hidden beneath the sheetmetal just below the control board). You should be able to order this kit through any appliance parts store for around 175 dollars versus almost
800 dollars for a new PTAC. Hope this is helpful.

Had this exact problem. Remove cover and then remove the white plastic shroud from the top back portion over the coils. there are three 1/4" inch screws to remove one on the front right and two on the left and right of the cover.
Vacuum the enormous amount of lint collected on the interior/fan side of the coils. The unit will now blow cold properly.

Probably low on freon, requires a refill.