RedZR

Hello,

The first round of "owner vs. defroster" is over and I have lost. My 78 has a problem where I can not get the vent seletion to change from the floor vents to anywhere else (like the defroster).

I installed a brand new control head (wilcox had it for $88) and nothing has changed- its still blowing on the floor vents. Does anyone have a vacuum diagram for a 78 HVAC system or give me any ideas on what to check next? I checked and do have vacuum at the control head that is coming from the black hose- so whatever is happening is after the switch (It would seem to me).The car is soooooo close- this is the last thing I need to fix!

Thanks!
Dan

78IndyPace

Link:

http://willcoxcorvette.com/instructi...82_secured.pdf

Hope it helps!
Jerry

leetownreb

That's all you have left to do?? Wanna trade PCs??

dar322

i went through a similar thing. take a good look at the back of the assy. make sure you have all the plastic protrusions properly lined up with the slots. that's how the vacuum select switch deflects air from from floor, vents, defrost.

jdp6000

But if that fails. You may need to take out your center cluster and access the box which directs the air flow. If you have the side panel off you maybe able to see back there but not much.

Jim

RedZR

An update- I used my vacuum pump and can operate all of the accuators from the back of the vacuum harness that connects to the switch. Everything seems to hold vacuum- I am stumped.

Dan

...Roger...

If all the actuators work and you have vacuum to the 5 port valve then the valve is bad,blocked or leaking.
port 1 is source
port 3 is for defrost

RedZR

Ok- this just keeps getting better. I removed the vacuum harness from the back of the switch and while the engine was running I made a "jumper hose" to test the individual ports. I pushed one end into the source (31) and the other into #3 and the air was diverted to the defroster (good). I then jumped #1 and #4 and the air diverted to the dash (good) and then #1 and # 5 and the air was routed through the bottom vents, but I could head the door on the outer side if the firewall opening.

I can also hear a very faint vacuum sound coming from the controller. When I move the two pieces of the controller together (where the vacuum hoses mount) the sound stops but the air will not redivert. I am confused as to why I have enough vacuum when I dod my jumping deal- but not when its assembled.

Could I have gotten a bad valve assembly from Wilcox?

Any thoughts??
Dan

jdp6000

Have you tampered with it? There is a rubber patterned disc in that controller. Its like a maze. It diverts the vacuum. It has to be installed in one place and in one position. It will not work if its posistioned wrong.

Jim

RedZR

Nope, I have that covered. I installed the new switch without modifications. I am totally out of ideas and am thinking about getting yet another diverter assembly and replacing all the hoses (although I am not sure if the hoses are the problem since everything seems to hold vacuum.

RedZR

Ah heck- its getting cold here in the Mountain State and I could not dump a car on you that has no defroster

How is yours coming ?

...Roger...

Since you jumpered the vacuum and got everything to work it sounds like the problem is in the 5 port valve. Ive seen new valves over lubed which plugs them up.

RedZR

Roger- you have taught me well! I checked for that by taking the new unit apart and cleaning it. Is it usual to hear a slight hissing sound from that unit when the car is running?

Dan

PS Thanks for all of your help. I really owe you!

RedZR

I got it !!!!!!!

The new vacuum selector I purchased was bad. I was hearing a vacuum leak when I had it on the car. So, I removed the little vacuum routing thing (where the harness plugs into) and replaced it with the old one that I had cleaned up and it works !!!!!!! I now have defrost and vent air on all settings!!! While switching it I can hear all of the doors opening and it works like new.

The only downside is that while removing the little pin from the new assembly (that holds the selector together) I broke one of the pin's latches. I replaced the entire pin with a small screw and nut arrangement and used a washer to help hold the spring in place. I actually like this arrangement better than the pin since it helps the unit seal better as you can adjust it via tightening up the screw. No clearance problems because the screw was perfect length and I used a dab of Loc-Tite to hold it. It isnt NCRS, but it will do the trick !!!

Thanks to all for their input and help- especially Roger!
Dan

hunt4cleanair

Dan...couldn't figure out what component you were talking about...but now I got it...actuators!

...Roger...

Dan ,
Glad you got it fixed and I'm sure you realize by now the hiss is not a good thing.
On the new rubber directional vacuum thingy, could you see where the maze was not made correctly ?
Putting the screw and washer through the valve is a good idea Ive been doing it for years using a nylon screw and nut from Lowes that has a rather large OD head. I also have a small box of the original push pins but as you said the adjustable screw is an improvement.

dgood

I was not getting heat from my vents, only to my floor. I pulled everything off the dash to look back there and found a bad hose. I was testing all the positions and noticed that the valves to out side air down by the passenger side kick panel and the one in the engine compartment by the passenger side window pillar were not opening. When should these open? In the economy/vent position? If so, do you think my 5 port valve is bad. These hoses are good and that looks like the only thing that they have in common. I manually pushed open the valves and the move in and out.

lasmith03

I had this same problem on my 78. I replaced the selector with a new one but the defroster position wasn't working. But if I squeezed the switch it started working. I'm going to try replacing the pin with a screw and nut as you suggested. I'll let you know if this fixes it.

lasmith03

Finally got everything put back together tonight and its fixed. The plastic pin wasn't holding the new switch together well enough. So I just cleaned up my old one, replaced the broken pin in that switch with a screw and a nylon locking nut. Everything works fine. I did have to put some washers in between the switch and the mounts so that the screw head would clear the mechanical arms of the slider. But no prob.

lasmith03

The other thing that helped when diagnosing and fixing my vacuum switch and lines was this Wilcox video. I used this method to repair the connections at the firewall grommet.

http://www.youtube.com/watch?list=UU...atZzTTANU#t=72