cody laws

Alright I bought a new van. 99 express 3500. Just got a new heater control valve instaled. Big pain in the neck. But Im still not getting any heat. I found a couple of broke vacuum lines in the back of the switch control. How do you fix these little hoses? And is there a way to make blow hot without fixing those lines? THANKS

oldchevy

You don't fix the hoses, you replace them with new ones. You need to replace them so you have the option of switching from heat to cold.

dberladyn

Why do they use engine vacuum as opposed to an electrical servo to control those vents? Cheaper? Maybe that's not right as a mechanical cable would be cheapest. At least design and immediate implementation wise. But why the vacuum lines? I have always wondered. It must be cheaper overall.

Off topic, my uncle had a Cadillac with hydraulic windows.

StanVan

Probably stems from a time when electricity was not as plentiful in cars than it is today. In my '74 P20 Step van, I upgraded my alternator from a 42 amp to a 60 amp. And vacuum is there, why not put it to use?

dberladyn

Good points. My money is on cost. Vacuum is probably the cheapest most reliable means.

cody laws

I put the junk van actuator on. It's pushing heat in the defrost but no where else. I repaired the lines to switch control. But nothing but defrost. I've looked at all the lines everything is plugged into

dberladyn

That's the most important spot, at least you are that lucky.




Have you removed the HVAC controls themselves and looked at the back? This is where those lines plug in.

If I was you, I would take a bic pen apart (or something similiar) and try plugging the hoses one by one into each other. Try and see if you can get anything to move. You could do this in the passenger foot-well perhaps. In the passenger foot-well there is that "T" fitting. The singular tee fitting where all the lines reconnect to each other. That tee is suppose to be plugged so it is just a straight line with no branch connection. At least it has been everywhere I have seen it ( except on vans where people had problems ) . Make sure that "tee" is capped. If you have to just put your finger over it and move the dials. I suspect that it is a test line for testing in situations like the one you have right now.

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1999 GM Savana / Express - HVAC Vacuum Schematic



1999 GM Savana / Express - HVAC Vacuum Schematic

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StanVan

Nothing but defrost usually means no vacuum at all. Check the source.

dberladyn

Nope. No Vacuum means Outside Air is ran through both Heated and not-Heated channels then vented inside the cab by means of the Instrument Vents and Defrost and Floor. Makes sense to do that. It's in the diagram. However, as long as the system holds a vacuum, the valves should stay as you last left them via the controls.

( You've had me double checking and double-checking, but that's the way it is. As I wrote it. )

StanVan

My Astro had an inherent vacuum issue (they all do, and GM never fixed it). On a moderate to long uphill, the reservoir ran out of vacuum, and as it was explained to me, it was made to default to defrost, because keeping the windshield fog free is more important than anything else. Makes sense. And it also makes sense that all cars do that. The guy could have been handing me a big ole butt load, but it does make some sense to me.