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73-87 Chevy _ GMC Trucks => 73-87 Chevy & GMC Trucks => Topic started by: devildogmech on April 19, 2018, 10:42:50 PM

Title: What is this?
Post by: devildogmech on April 19, 2018, 10:42:50 PM

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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Title: Re: What is this?
Post by: Jason S on April 19, 2018, 11:23:24 PM

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

Title: Re: What is this?
Post by: Rapid Roy on April 20, 2018, 06:16:19 AM

Welcome to the site.

Title: Re: What is this?
Post by: Henry on April 20, 2018, 11:04:15 AM

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

Title: Re: What is this?
Post by: devildogmech on April 20, 2018, 05:03:53 PM

Quote from: Jason S on April 19, 2018, 11:23:24 PM

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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Title: Re: What is this?
Post by: devildogmech on April 20, 2018, 05:05:21 PM

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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