What is this?

[devildogmech]

Hey all,

This is from a 79’ C-10. It’s pretty well loaded, with AC, Tilt, Cruise... ext

There is this “pot” looking thing on the passenger side of the firewall. It has a manifold vacuum line going to it, and then a vacuum line going through the firewall into the cab.

Is it some kind of vaccine reservoir for the climat Control’s?

It’s just left and above the AC box on the firewall.

I don’t remember my 78’ C-20 having this.....

TIA!





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[Jason S]

You're correct - Vacuum reservoir for the HVAC system.  Was the '78 C-20 a heater only truck? 

[Rapid Roy]

Welcome to the site.

[Henry]

Hi Devildog:
Yes, Jason is right, this is the vacuum accumulator or reservoir for the HVAC...when you slide your AC system selector lever on the dash all the air door settings are controlled by vacuum. The temperature selector lever uses a flexible mechanical cable for its settings. On a truck without AC, you will not see this vacuum accumulator can...the non-AC truck uses a flexible mechanical cable for all the air door settings.

You can usually tell if the vacuum accumulator is actuating the air door by sliding the AC system selector from "off" to "vent" and you will hear a soft "clunk" within a second or two which indicates the air door has moved. If you dont hear the clunk and do not feel air coming out the vents then either the accumulator is not holding vacuum or the vacuum servo at the air door is not holding vacuum anymore...or one of the connecting vacuum hoses is leaking.

Regards,
Henry

[devildogmech]

You're correct - Vacuum reservoir for the HVAC system.  Was the '78 C-20 a heater only truck?

Yup, exactly. This one is AC, so there is a ton more stuff under the hood


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[devildogmech]

Thanks all. I pulled the AC compressor as it wasn’t working anyways. System was uncharged.

One day, I’ll get the HVAC system working. Just not anytime soon.

Thanks again!


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