1995 Buick Park Avenue

Heater problem
1995 Buick Park Avenue 6 cyl Two Wheel Drive 177, 00 miles

Yesterday, I had AC compressor, A/C accumulator and A/C Orfice tude replaced on my l995 Buick Park Avenue, 6cyl 3.8. When I drove it home last night, the AC works, but I am not getting any heat when I turnon the AC button and raise the heat button to 75, I get cold air. However, when I push the vent button, after the car warms up, I get hot air, but not really hot. What is wrong now?
February 24, 2008.

I would check the thermostat
replace thermostat and check the heater core

Feb 24, 2008.