Semi-Functiional floor heat.

[88MercWagon]

Hey guys, when put on the "floor" setting, it seems as if the blend door either doesn't fully open or is broken, since I get some air coming out of the floor vent, and some out of the defrost, at roughly a 50/50 split. What could cause this? A bad vacuum motor for the floor function? Also, if it is a bad motor, could it cause a vacuum leak even when not being used, such as on the vent function? Data for the application is below.

Car: 1988 Colony Park
Manual Climate control
100% stock, all original parts such as EGR, charcoal canister, etc intact.

Thank you in advance for your assistance.
-Nick

[sly]

there could be a vacuum leak. you'll need a vacuum pump (hand pump is fine) and connect it to each actuator under the dash to see if that's the problem. If it is... replace the leaky one.

It could also be the check valve that Ts off to the "soup can" under the hood (been there, replaced the one on my 88 already).

If you set it to defrost does it still come out the floor? If so... then it's probably a broken hinge on the vent control door which requires taking the whole dash half way out to get at the entire air duct system and pull the works out to fix the problem. I've also seen issues where screws/etc dropped down the defrost vents will keep the doors open and prevent them from sealing up good.

[gadget73]

sounds like busted air doors in the plenum assembly, or at least one broken door. When my car was doing this, both doors were broken and air came out of everywhere. If thats the case, the only fix is to remove the plenum and rebuild the air doors. I have small steel hinges from the hardware store replacing the original broken plastic hinges in the box.

[88MercWagon]

there could be a vacuum leak. you'll need a vacuum pump (hand pump is fine) and connect it to each actuator under the dash to see if that's the problem. If it is... replace the leaky one.

It could also be the check valve that Ts off to the "soup can" under the hood (been there, replaced the one on my 88 already).

If you set it to defrost does it still come out the floor? If so... then it's probably a broken hinge on the vent control door which requires taking the whole dash half way out to get at the entire air duct system and pull the works out to fix the problem. I've also seen issues where screws/etc dropped down the defrost vents will keep the doors open and prevent them from sealing up good.

Nope, defrost works just as it should, as does vent. I also replaced the check valve as a precaution, and it didn't change anything.

[sly]

there could be a leak in the line to the floor vent side of the actuators (they are dual action I think... vacuum to one side goes to one vent... vacuum to the other side goes to the other vent position). You may have a leaky actuator or just a broken/disconnected hose.