Hvac
Thread Starter
Instructor
Joined: Feb 2007
Posts: 132
Likes: 3
From: CRYSTAL RIVER FL.
Hvac
1992 LT1 C68 electronical automatical type.
No codes showing on control head. Fan controls work up and down.Lights work on all function buttons. Temp set works.
Air only blows out of upper (defrost/defog) vents and foot well vents. Nothing out of center dash vents.
Looking at FSM section 1B-12 Fig. 10.
Have vacuum to the programmer. Showing five vacuum motors and one blend door. Also on page 1B-30 Fig. 24 it shows a temperature door motor, or blend door actuator.
I've had these blend door actuators fail on other GM cars. But not the vacuum motors. Read thru the entire 1C1 section and not much info other than codes.
Anybody have this problem?
Thanks, Dave
No codes showing on control head. Fan controls work up and down.Lights work on all function buttons. Temp set works.
Air only blows out of upper (defrost/defog) vents and foot well vents. Nothing out of center dash vents.
Looking at FSM section 1B-12 Fig. 10.
Have vacuum to the programmer. Showing five vacuum motors and one blend door. Also on page 1B-30 Fig. 24 it shows a temperature door motor, or blend door actuator.
I've had these blend door actuators fail on other GM cars. But not the vacuum motors. Read thru the entire 1C1 section and not much info other than codes.
Anybody have this problem?
Thanks, Dave
Melting Slicks
Joined: Oct 2016
Posts: 2,024
Likes: 363
From: Central Alabama
Don't see it being a blend door. Blend door adjust air source, heater/evap core before any directional routing. It sounds a lot like loss of vacuum to the door controls. Have you checked the check valve under the passengers side injector cover? Common failure point that would cause a loss of vacuum to operate the directional doors. Could be a broken line but the valve is easy to check. You can also apply vacuum manually and see if it starts working with a vacuum pump.
It sounds like the doors have simply moved to their resting position. They are designed to fail in a manor that allows the windshield to be defrosted. Could also be internal failure of the controller (on the firewall) or the push on vacuum connector.
It sounds like the doors have simply moved to their resting position. They are designed to fail in a manor that allows the windshield to be defrosted. Could also be internal failure of the controller (on the firewall) or the push on vacuum connector.
Thread Starter
Instructor
Joined: Feb 2007
Posts: 132
Likes: 3
From: CRYSTAL RIVER FL.
Yep I know I.m going to go under the dash. Hate that. Just looking for the vacuum motor that might be the one at fault. FSM doesn't really get into too much detail about which one does what.
Thanks, Dave
Thanks, Dave
Heel & Toe
Joined: Feb 2018
Posts: 23
Likes: 1
I just fixed this on my '90, assuming your solenoids are working in the programmer, there is a black plastic vacuum line found more clearly on passenger side under glove box, it ends at the programmer but begins at a T near the distributor up through the firewall. That T gets source vacuum from manifold and it distributes to that black plastic line as well as another T near wheel well which then goes to the cruise control vacuum valve and the vacuum ball in the front driver side corner where horn is. it connects those using rubber 7/32 and 5/32 vacuum hose. Previous owner had broken that black plastic line by distributor and needed all those hoses replaced. Once I connected that black plastic line through the firewall my door that diverts airflow from default defrost position to front central position moved again under proper vacuum and had nice blast of air through center vents.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 207
From: Orlando FL
Don't see it being a blend door. Blend door adjust air source, heater/evap core before any directional routing. It sounds a lot like loss of vacuum to the door controls. Have you checked the check valve under the passengers side injector cover? Common failure point that would cause a loss of vacuum to operate the directional doors. Could be a broken line but the valve is easy to check. You can also apply vacuum manually and see if it starts working with a vacuum pump.
It sounds like the doors have simply moved to their resting position. They are designed to fail in a manor that allows the windshield to be defrosted. Could also be internal failure of the controller (on the firewall) or the push on vacuum connector.
It sounds like the doors have simply moved to their resting position. They are designed to fail in a manor that allows the windshield to be defrosted. Could also be internal failure of the controller (on the firewall) or the push on vacuum connector.
Most likely problem for this is the 3 hose check valve under the plastic cover on the engine. You can still have vacuum but unless you have full vacuum the vents may not move. The vacuum also drives the cruise servo. The cruise can work OK while the vents will not. Look for any cracks or breaks in the check valve.
Oil Producer
Joined: Apr 2014
Posts: 9,387
Likes: 2,749
https://www.corvetteforum.com/forums...post1596578045
many times the vac line which enters into the main harness rearward of the dizzy gets broken. = loss of vent control.
many times the vac line which enters into the main harness rearward of the dizzy gets broken. = loss of vent control.
