Low amount of heat from upper vents

[bigbadbronxy2k5]

Ok, I searched (maybe not carefully enough) and couldn't find anything like this here. I have heat no question, but even on full blast it only trickles from the upper vents. Now, on the other hand turn on the A/C and it pours out. I can hear the vents moving and the blower is blowing, naturally. I'm guesssing the heater core is ok, 'cause I have heat. Any ideas? BTW, the car is the 99 Lumina 9c3 police package.

[brcidd]

I can tell you that certain model cars are designed to "damper" the heat when air is asked for at the vents- Most designers avoid putting full heat in people's faces- to avoid that complaint-- likewise the systems are designed not to put full a/c cold on the defrost (windshield)- I know for a fact the later model U-vans have damper doors to restrict the flow of heat out the vents when on full hot- the actuators actually throw a secondary door to restrict the air flow out the vents when in full hot mode--I have had folks complain about this- and there is a TSB on it in the U-vans (Montanna, Silhouette, Venture) to disable the secondary door- if they complain. It is pretty simple- most folks want heat at their feet, and cool air in their faces- not heat in their faces. I once worked on a ladies car who wanted full a/c cold air to come out the defrost- but there was a whistling noise-turned out to be the secondary air dampner door at the defrost- You can look at your actuators and see if your vehicle has a secondary door- It will have two arms on it- and the TSB said to simply disconnect one of the arms....

[bigbadbronxy2k5]

Originally Posted by brcidd

I can tell you that certain model cars are designed to "damper" the heat when air is asked for at the vents- Most designers avoid putting full heat in people's faces- to avoid that complaint-- likewise the systems are designed not to put full a/c cold on the defrost (windshield)- I know for a fact the later model U-vans have damper doors to restrict the flow of heat out the vents when on full hot- the actuators actually throw a secondary door to restrict the air flow out the vents when in full hot mode--I have had folks complain about this- and there is a TSB on it in the U-vans (Montanna, Silhouette, Venture) to disable the secondary door- if they complain. It is pretty simple- most folks want heat at their feet, and cool air in their faces- not heat in their faces. I once worked on a ladies car who wanted full a/c cold air to come out the defrost- but there was a whistling noise-turned out to be the secondary air dampner door at the defrost- You can look at your actuators and see if your vehicle has a secondary door- It will have two arms on it- and the TSB said to simply disconnect one of the arms....

The mystery whistling noise! I hear like a whistling when the face vents are on, but I hear that noise while the a/c is on too, but the a/c pours forth like no tommorow. The noise is on and off, no vacum leaks detected.

[rhandwor]

Feel both heater hoses and make sure they are hot. A partially plugged heater core will cause this problem. If one hose is a lot hotter than the other one this is your problem. Otherwise check for a broken blend door a common problem on some vehicles.

[Blue Bowtie]

Generally, that is correct. However, there will be a noticeable difference in the temperature of the coolant hoses for an idling engine when ambient temperatures are lower and the heater blower is moving a relatively large volume of air.

Mornings here have been between 5-10ºF in the past several days, and if the weather in the Bronx is similar, a difference in hose temperatures should be expected unless the blower is off or the engine RPM is well above idle.

[vtwindave]

check vacuum line going to vac resivoir. (it may be by the battery) if vac line has hole or is broken the air flow will come out vent/ac ducts cause n ot enough vacuum is reaching switches to move doors to direct air flow to defrost ducts. had same problem on corsica & lumina