gsimon767

According to Dr Rebuilds catalog early 75 does not use a heater hose shutoff valve but late 75 does. See the diagram out of the Dr's catalog. My 75 is a June 19 build so I would think it is a late 75 and should have the shutoff valve. Can anyone verify the existence or not of a shutoff valve in a late 75 car or any 75 for that matter?

According to the Dr's diagram there should be a white vacuum hose through the firewall going to the shutoff valve. Somewhere in my cars past ownership someone cut a hole in the firewall where a vacuum actuator can exists with a white striped hose leading back inside the dash. Could the vacuum can be the item B in the diagram? See the pictures.

I do not know where the white hose is leading to without taking the interior apart. There is resistance when I pull on the white striped hose so it may be attached to something.Can anyone with experience with the vacuum hose routing explain what the white hose does on my car? Is it the elusive white striped wire to the heater control valve?

I am cleaning up the firewall and patching the hole so if at all possible I would like to use a shutoff valve whether or not there should be one present. It will help keep interior temps down and help the AC work better.

Jud Chapin

I'm under the impression that the '75 didn't have one although the '76 did. I had both cars and remember doing some research finding that the '75 did not have one which i thought rather strange at the time. As I recall, this research included checking the "Assembly Manual" which showed no valve at any time during the model year.

gsimon767

If 75s did not have a control valve can anyone who has had the heater air plenum apart tell me what the white striped hose in my picture is for. The only reference I can find for the white striped hose is for a heater hose control.

Somebody must have had one of these plenums out of the car and know what the white striped hose is for?

Why would someone cut the hole in the firewall in my pictures?

ezobens

Was that hole intentionally cut out (badly) or is it perhaps due to someone not paying attention when pulling the motor and popping a hole in the firewall? It wouldn't be the first time I've seen that.
There really would be no other reason to have a hole there unless the PO was a bubba and needed to get to that vacuum diaphragm on the HVAC for some reason and was to lazy to get to it the correct way.

GM seemed to waffle on the hot water valve every few years- Early models had it and then they dropped it in 71 or 72 and then back again in 76. I'm guessing the bean counters were to blame.

Easy Mike

White indicates the color of the stripe on the hose. The hose itself will be black with a white stripe. Per the Dr.'s diagram, black with a white stripe went to the shut off valve.

gsimon767

I meant to say white striped hose. You can see in the picture that it is a white striped hose in the hole in the dash. If it is not for the shutoff valve hose what is it for?

jnealg

mine has a born on date very near yours and it did indeed have a shut off valve. black pancake with vac line attached.

dochorsepower

Keep it simple and just block off the heater connection.

Paul L

That works.