92 S10 heater vacum problems?

I have not had any air coming from the heater of my 92 S10 Blazer for months now. You can hear a load hissing (vacuum leak) in the vent control area on
the dash.
I went to a junk yard and got a new unit, replaced mine and the leak is now gone. The little part that all the hoses connect to was leaking badly.
I still do not have any heat. If I reach down behind the vacuum assist on the heater area there is a spring loaded metal arm on the side of the duct area. If I grab it and pull on it I have heat. If I manually move it back I don't.
Is this part of the vacuum assist assembly or a separate part?
Can it be replaced?
Lannie
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It appears that if I manually pull it so I have heat, it goes to defrost if I give the truck a lot of gas like going up a hill. Once I let up it goes back. Same when on vent.
Is the vacuum assist on the heater leaking? I cannot hear it anywhere. I've checked every host under the hood and what I can find under the dash and can find nothing wrong.
LS

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Helloooo?????

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Sounds like your vacuum control valve is leaking. It is located right behind the control lever on the dash. You can remove the valve and pop it apart and coat the parts with vacuum grease, or simply replace it the valve. Regards, JR
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I have a new one in which did not fix the heater problem but did fix the leak.

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