Try to use the normal AC (not MAX) when the engine is cold in the morning. If you get cold or cool air when the engine is cold check the hot water valve for function. If you have one, put a vacuum gauge on the hot water valve vacuum line, right there at the hot water valve end (it's a pretty obvious vacuum, so you can use your finger too...). See if the vacuum changes as you request warmer air / colder air. You should feel strong vacuum on that line when you request cold air and a gradual decrease in vacuum as you request warmer air. The hot water valve actuation arm will move back and forth with the vacuum. The actuation arm should be sucked in to close off hot water to the heater cores when full vacuum is applied through that line. If there is vacuum present but you do not see the actuation arm being sucked in the hot water valve is bad and should be replaced. If there is NO vacuum present your problem is in the vacuum line and you'll need to trace that from the supply side vacuum line, through the control module (under the dash at the front end of the center console...), and back out the firewall to the hot water valve. If you follow the hot water valve vacuum line to the firewall you should see the supply line from the engine source going through the same pass-thru grommet in the firewall. Make sure that line is in good shape and no leaks. That should get you started on troubleshooting it anyway.....
Hot water valve ....
Vacuum lines at the firewall .... left is supply, right (shrouded) is line to hot water valve....
