vacuum line help.

[DM75Hurst]

I have a line connected to my cold air intake on a choke valve of some sort labeled "autotherm ac" going to the bottom of my air cleaner housing to another part labeled "ac" or along those lines.. then out of that to the top of the intake manifold directly behind the carb..

Simple picture: O<---->o<----->(Manifold) (hope that helps LOL)

My question is: What does that "autotherm ac" valve do? And if i replace my stock cleaner box with an open element style, can i just plug that line or do i have to do something special with it?


edit, this is an A/C car, but a/c does not work (it did before it sat 18 years, i'm sure that the magic gas leaked out sometime during that period) And i'm probably not going to repair the A/C anytime soon..

[1977 Cutly]

I plugged mine without any issues.

[Mike 77]

Those are your cold start air intake control. The valve or damper in the air cleaner snorkel will either allow air to come from the front of the car or from the exhaust manifold. You should have flex metal tube from the bottom of the snorkel to the metal heat riser plate on the exhaust manifold. Also a plastic flex hose and funnel from the snorkel to the front header. The damper opens and closes via vacuum, controlled by a small round thermostat located in the air cleaner base. When the car is cold the carb sucks in warm air from the heat riser and cold air from the front when the air is warmed up.

Mike

[58thndy]

Just cap the vacuum port on the intake if you decide to use the open element airfilter. You'll notice it has a very small pinhole opening compared to other vacuum ports.

ThermAC was simply part of emissions control equipment. The idea was to preheat air to the carb to reduce emissions on cold start.

Components: vacuum operated flapper valve in aircleaner snout, shroud covering the exhaust manifold, heat tube from aircleaner to exhaust manifold shroud, and a temperature switch inside aircleaner on carb side of the filter.

When dead cold (overnight) the temp switch closed off outside air to the flapper in the snout, forcing intake air to come from the exhaust manifold shroud where it was heated. The heated air traveled thru the heat tube and into the carb. As the engine warmed up, the temp switch modulated vacuum to the flapper allowing mixed warm/cold air to the carb. After the engine reached operating temperature the temp switch opened the flapper completely to outside air allowing 100% cold air to the carb- or as cold as underhood temps allowed.

The cold air induction concept worked better after they started using the flex hose and OAI nozzle at the core support. See, your late-70s smogmobiles actually benefited from Oldsmobile's famous W-Machine Outside Air Induction research!

ThermAC had the added advantage that it also virtually eliminated carburetor icing in cold climates, since if ambient temp was very cold it would modulate warm/cold air to the carb keeping it above icing temp.

I never saw where a ThermAC affected performance that much unless the temp switch failed completely and kept the engine running on heated air in hot weather. The flapper was vacuum close/spring open so unless it had vacuum directed to it, its fail position was open to outside air.

[zodiacblue442]

Mike and 58thndy - EXCELLENT explanations.

[DM75Hurst]

Thanks guys!! sorry for the very late response. PC took a crap on me and i kinda forgot about the forums since it wasn't in my bookmarks anymore.... I put on a open element air cleaner and removed the snorkel box, metal flex tubing and capped the vacuum line. It runs ok, was just hoping i wasn't going to cause any damage by doing so.