'99 W210 E300D

Sometimes...not always....when the car is started up and AC is on....there will be cool AC from the drivers side and center vents....but passenger side and rear seat vents have heat coming out.

?????

Also sometimes when temp is set to 70, in the mornings when outside temp is 55-60, when the car is started it blows cold AC....when it seems a bit of heat is needed. brrrrrrrrrrr!!

?????????

Need "Tips" for diagnosis and fix.

What diagnostics to run?

thanks
Warren C.