I have a 1999 Caddac DeVille . The AC works fine during the summer but in the winter it won't blow out hot air unless I'm driving. I've let the car run in the morning to warm up but the inside is always freezing cold. I also want to know if the heat is suppose to blow through the panel vents because it only blows heat from the floor and windshield vents. and it only blows through the windshield and floor vents. If I'm parked it won't blow anything but cold outside air. What's the problem?

SOURCE: Intermittent AC and Heat w/ long gaps of hot(for AC) or cold(for heat) air

I had similar problem on my 2001 Insight. Had to replace some cooling system hoses eaten by rodents... Works like a champ again.

SOURCE: heat always blowing on floorboard when driving even in off mode.

on the bottom of the heater case is a vaccum door right on top of the hump it has a white plastic adaptor that breaks replace with dealer part it just pops off

SOURCE: 2004 Odyssey, heat and A/C do not work unless van in motion

Since warm air eventually comes out when the vehicle is in motion, you may have an air mix door that is stuck in fresh or is somehow blocking warm air from the heater core.

To see if the air mix control motor is bad, you need to retrieve your Diagnostic trouble codes (DTC's) from the heater control panel. To run the diagnostic function, do the following:
1. Turn the ignition switch ON (II).
2. Turn the fan switch OFF.
3. Press the recirc control button to select Recirc (recirc light on.)
4. Press and hold the recirc button to select Fresh (recirc light off) and continue to hold the button down until the recirc light comes on for two seconds and then goes off.
5. If the system is okay, the recirc light stays off.
6. If there is a problem, the recirc light blinks the DTC to indicate the trouble. One blink=a problem in the air mix control motor circuit. Two blinks=problem in the mode control motor circuit
Three blinks=problem in evaporator temp sensor circuit.
7. Turn the ignition switch off to cancel the self diagnosis function. Run the diagnostic again after repairs are complete.

Note: the air mix control motor has a rod which connects to a plastic link. The link controls the mix doors and also connects to the heater control water valve via a cable. The air mix motor may check okay, but if the link is broken then you will still have problems. the motor is on the bottom of the heater unit in the front passenger's foot well.

SOURCE: I have a 1999 Buick LeSabre. My AC blows cold air

the vents are run on vacuum so if you get the others just not vent sounds to me like you need to find your junction and see if all the hoses are hooked up. mine was passenger side above where ur feet go. All that usually happens is a hose came off and u need to put it back on sometimes they break but u will be able to see once u find it.

SOURCE: When I start my car in the morning and its warmed

sounds like your thermostat is stuck open and over cooling. hope thats a little help anyhow