Let's play, name that part...

[sbx22]

Hey guys, always appreciate the help I get around here to build up my street truck. Anyway, I took this part out when re-doing the engine bay and swapping the motor. Never knew what it was for. Can anybody tell me what it is and it's function? I have a hunch that it is a smog part?

[zieg85]

That part is a vacuum canister.  It holds enough vacuum to operate the HVAC stuff in the cab for when the engine is floored or under acceleration and is low on vacuum so it keeps the Defrost on defrost.  You need it hooked up or that top slider won't do anything

[sbx22]

Maybe that's why my a/c and heater have not worked the same since the engine swap. I will get this part back on asap! After doing some googling, apparently down the line from this, it is T'd off somewhere from a vacuum source (I don't know where), and then it stores vacuum to operate the a/c. I don't understand how this exactly works though with only one line plugged into one port. I want to understand how this HVAC system works and how it is hooked up. Appreciate the help.

[bd]

There should be a vacuum check valve between the "T" that connects the reservoir and HVAC vacuum control to the intake manifold.  So, vacuum routes from an intake manifold fitting, through a one-way check valve to the 'T', and from the 'T' to the reservoir and HVAC vacuum control.

[sbx22]

Should I expect some vacuum suction from this line that connects to the canister? The only vacuum sources I have connected right now are transmission, brake booster, PCV, and vacuum secondary. I couldn't possibly see where the vacuum canister gets its source of vacuum. I feel lost.

[bd]

Let's pause for a second.  There were several styles of vacuum reservoir used over the years.  How many ports are on your reservoir - 1 or 2?  The description I provided above is for a single port reservoir.

[VileZambonie]

Look at the pic

[bd]

Thanks Vile.

[sbx22]

Now that I looked at it again, there are two ports, one small, one large. I remember when I took it off initially, there was only one line connecting to it, and that was the small port. Does anything hook up to the large port? A full vacuum line maybe?

[Engineer]

That part is a vacuum canister.  It holds enough vacuum to operate the HVAC stuff in the cab for when the engine is floored or under acceleration and is low on vacuum so it keeps the Defrost on defrost.  You need it hooked up or that top slider won't do anything

Actually zieg when there is no vacuum the engineers designed the HVAC system to default to defrost. (The duct doors are spring loaded to open to defrost should you lose vacuum) This is one of those safety features so your windshield won't fog up at the worst times should you lose system integrity or in case of a vacuum leak.

[zieg85]

That part is a vacuum canister.  It holds enough vacuum to operate the HVAC stuff in the cab for when the engine is floored or under acceleration and is low on vacuum so it keeps the Defrost on defrost.  You need it hooked up or that top slider won't do anything

Actually zieg when there is no vacuum the engineers designed the HVAC system to default to defrost. (The duct doors are spring loaded to open to defrost should you lose vacuum) This is one of those safety features so your windshield won't fog up at the worst times should you lose system integrity or in case of a vacuum leak.

Thanks, I was guessing on which one it stayed on when there was no vacuum...  I have always had them working if I had an AC cab

[LTZ C20]

Was just poking around here. What Engineer said makes good sense because my system is stuck on defrost.

I thought it was because I got some hoses switched around when I did the heater core. Then I remembered that I had separated the lines and kept them in there proper area. While messing with my engine today, found the vac fitting behind carb was loose. Most likely why HVAC inop. Will fix tomorrow. Thanks Engineer.