Why isn't my 1990 cadillac deville heats not functioning?

first check to see if the blend door motor is working if it is then the temp module may be the culprit , also check the heater hoses to see if they are hot on both side the inlet and the outlet you can do this by feeling them . let the car heat up to operating temperature then feel both hoses if one is cold and the other on is hot this indicates a flow problem , if this is the problem check the temperature of the engine , if the engine does not reach operating temp then replace the thermostat and then recheck engine temp , check the flow of the heater core , you can do this by pulling the hoses off and use a garden hose to push water through the heater core " do not turn the hose on high "

Sound like it could be a bad thermostat or maybe low on anti freeze or bad water pump. Does the engine overheat at all?

Feel the 2 tubes at the firewall for the heater core. If they are not getting hot, the heater core needs to be flushed out or replaced. I had this problem with a 1990 Cadilac Deville, it was just a plugged up heater core.

Remember to install sealant after flushing out the system to prevent leaks.

Touch both heater hoses going to the heater core. They should both be hot. If they are, then the problem is probably a broken or binding blend door or bad blend door actuator. If one hose is hot and the other cold, then the heater core is clogged.

Since your blower is working and it is a heat issue,thats where we'll start,First thing is have you checked the coolant level in the radiator when engine is cold,make sure it is filled to top,next verify you have coolant in reserve ,Start your van and get it up to normal operation temperature,If your heat gauge on the dash works correctly it should be 190 degrees,Now lift the hood and locate the two heater hoses going into the heater assembly at the fire wall,Both hoses should be hot to hold on to,if both are hot and no heat inside your problem will be the blend air door in heater assembly.
if neither hose is that hot you need to replace the thermostat in the engine to get it up to 195 degrees.
if one hose is hot and one is luke warm then the heater core is blocked and to blame. hope this helps you.To verify engine temp,leave the cap off before you run engine and check with a thermometer

I would check the main swicth that turns your blower motor on, because it dose operate by vacum. maybe you have a damage hose somewhere for the switch or controls.
good luck

do the heater core coolant supply hoses both get hot at the firewall in the engine compartment? if yes then you have a defective temperature control blend door actuater motor.

4.6 Northstar V8. It is located on the rear of engine (driver side) in front. It is 1n the the waterpump housing cover. Remove airbox and intake tube and bottom radiator hose. 2 bolts(believe 10mm) on thermo housing. These systems are a lil finiky about air pockets....so fill slowly and let run at idle until operating temp and let cool and chk level.....fill as needed and repeat if needed.

How old is your Battery? at the Temp. Stated above an Older Battery even though Good may not have Enough Cold Cranking Amps Left to Kick her Over.

the first thing to check is to have the engine running. as soon as it reaches operating temp the upper radiator hose should get hot. if it doesn't then it's the thermostat. if it does then i believe your water pump is probably not circulating like it should and it should be replaced. however before replacing the wter pump make sure that the wire to sending unit is tight and not giving you a false reading. if your model has electric fans make sure the fans are running when the engine is hot. if they are not running check the relay in the fuse box for the fans with the engine running switch out the fan relay with the a/c clutch relay. ifthe fans kick on replay the relay with a new one. if they don't click on the it's either a bad wire or the temp sensor probe is bad. hope this answers your question. please rate this solution...thanks.