How many vacuum lines run from engine to heater/air con.block

Maybe the vacuum line to the selector is disconnected/leaking /bad. Most of the vacuum controlled systems I have worked with also have a vacuum amplifier somewhere under the hood that increases the amount of vacuum going to the selector.

Could be one of three things but it sounds like your thermostat is shot. It's a spring loaded disc in the coolant system between the lower rad hose and the engine. When the spring lets go, it will let coolant flow through without resistant. If it goes through too fast in the winter, it won't build up any heat. Check the temperature of the engine. If the gauge (if you have one...) shows the engine is running at normal temp, it's not the thermostat. Squeeze the rad hoses after the car warms up and there should be pressure.
If it's not the thermostat, it could be a blocked heater core. The heater core is a little radiator like thing inside the car under the dash. Check the rubber coolant lines going through the fire wall and see if both are hot. If one's hot and the other is stone cold... blocked heater core.... Not a weekend warrior job...
If it's not the thermostat or the heater core, it could be a vacuum line controlling the temperature switch. Most GM's temp controls are vacuum line operated. Other cars have mechanical linkages. I'm not sure what kind of car you have..

sounds like you have air in the system, take the top off the water bottle and fill to the top run engine until fans come on and up to temp. keep filling the bottle so its at the top have the heater on but on low blow or no blow squeeze the pipes wile warming up to help move the air. you should see bubbles coming out the bottle when at temp turn the engine off and leave to cool down. you may need to top up now. but dont top up with water top up with antifreeze. put top back on and it should be fine. if not repeat. also check the valve is working and not blocked on the control for water direction will be electric type or vacuum type electric type should click when it is working vacuum type it runs off the engine vacuum line look for a leak in the line. and replace if it has a leak.

It sound like the is a vacuum leak in the line that goes to the heater control head. Engine vacuum is used to move blend doors in the heater box. There is a vacuum line that goes from the engine through the firewall on the passenger side up to the heater control head. I would check and make sure you have vacuum there with the engine running.

Probably a vacuum motor on the blender door has gone bad or the vacuum line broken or fell off.Find the blender door motor and with engine running,wheels blocked and emergency brake on in park,check the motor's operation. don-ohio

It sounds like vacuum is not getting to the vent, heat and A/C controls. Find the vacuum can. It may be under the hood on one of the inner fenders. Trace the lines back to the vacuum block at the intake manifold or fire-wall, and also back to where the line goes thru the fire-wall. Check the can for leaks or obvious holes. They used to be just a plain metal can, but it could be a plastic ball. Check the lines as you go for breaks and rub-thru's. Move the controls thru all settings and listen for vent door movement. (Run the engine momentarily to build vacuum in the system.) Worst case is a bad vacuum motor or air flow position selector switch.

another expert named:
telemachus

• Rank: Guru
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First, if the engine seems to take forever to warm up, you may have a stuck (open) thermostat. Replacing the thermostat would help get your engine to warm up quickly and maintain the proper running temperature of about 180 deg F. This would solve your heater woes.

However, if the engine warms up normally but the heater just doesn't seem to put out, check the heater inlet valve. This valve is usually next to the firewall on the engine side and is activated by cable(s) or vacuum lines. It is common to find that the valve cables have frozen, the cable ends have broken off, or the vacuum lines are disconnected or broken. Another common problem on vacuum run valves is that the vacuum diaphragm that operates the valve has failed. The diaphragm won't "hold a vacuum" meaning that it leaks and won't operate the heater valve.

If all that seems to work okay. The heater core could be getting warm coolant through it but the underdash heater air handler box has a movable door inside that is not in the requested position. These doors are operated by cables or vacuum lines---so same checkout as above.

The Intrepid doesn't have a vacuum line. It uses a electric motor called a "blend door actuator". It's located on the underside of the heater box near the center of the car.

LOOK UNDER NEATH VECHICLE ON LOWER BACK FIREWALL WHERE HEATER CORE HOSES RUN ON THE PASSENGER SIDE LOOK FOR SMALL EVAPORATOR DRAIN HOLE. TAKE A SHOP VAC AND SMALL VACUUM LINE HOSE ABOUT 3/8 SIZE VACUUM IN THE DRAIN HOLE THAT WILL REMOVE DEBRIS THAT BLOCKING OFF DRAIN HOLE WHICH KEEP EVAPORATOR WATER LEAKING INSIDE CAR.

Quite a few idea's come to mind.
1) Thermostat is stuck open, causing the engine to run cool.
2) The vacuum valve that opens and closes the air "flap" is stuck open, allowing cool air in all the time.
3) The vacuum valve that opens and closes the line that feeds the heater core isn't opening all the way.