Hi all,

2000 Dodge Ram Van 1500 with 5.2L V8.

I've had the issue where air only blows though the defroster. I found cracks in a gray vacuum line that comes though the passenger side of the firewall and runs to a round valve-type thing on a coolant hose. When I replaced the cracked vacuum line, I now get air only through the dash and floor vents. Nothing through the defrost.

Finally, I have a mystery vacuum line that's attached to nothing. It comes through the driver's side of the firewall, along with two other vacuum lines. One of those runs down to the motor. The other runs across to the passenger side into an actuator down low on the passenger side near the front bumper. And the third is just dangling under the hood connected to nothing.

Does anyone have photos of where these lines are supposed to run? I can't make heads or tails of the service manual on this front. Sorry, very new to vacuum controlled systems.

Thanks!

 

Have a look at the vacuum diagram that should be on a label under the hood somewhere. Verify all the various connections. *should* run across the one that's missing.

 

Thanks HY - is this the one? It's the only diagram I'm finding under the hood, but these don't look like they have to do with the heat/ac system.

 

The top is supposed to go to a heater valve, which appears to be missing. It should go right where that coupling, and 2 hose clamps are. The valve closes off the coolant flow to the heater core when the dash temperature **** is turned to cold. For the lower picture, it is hard to see much, but it looks like it for the EVAP system.

 

Thanks Alloro! That makes sense. Previous owner says he removed / bypassed the heater valve in a parking lot because the plastic cracked. That coupling is a T-connector, with three hoses coming off of it. The replacement heater valves I'm seeing online only seem to have two connections. Does the valve live between that T and the heater core, or am I missing something big?

Here's the replacement valve I'm finding

Greatly appreciated!

EDIT - never mind. I'm an idiot. The T is bc I have the rear heat/AC unit, and one of its lines runs into the T. The heater valve should go a few inches left of the T in the bottom image, I believe. Thanks again!

 

You are correct...about the valve I mean, not that you're an idiot.

 

Hey all - just want to add a post about how this ended up, in case anyone else ever stumbles onto this thread.

1) Mystery Vacuum Hose - as Alloro said, the gray vacuum hose that's connected to nothing should connect to the . Previous owner removed this bc it was leaking and replaced with a length of radiator hose.

2) Previously Cracked Vacuum Hose - this is an aftermarket addition made sometime in the past. It runs through the firewall in a separate location from the other vacuum hoses, and activates a second heater valve, which I described as a "valve-like" thing.

3) "Valve-like" thing - my van has a rear AC/heat unit located in the rear driver's side corner behind the wheel well. The service manual mentions a rear AC/heat unit, but the one I have is different from what the manual shows. According to the manual, the stock rear AC/heat unit is supposed to run off a cable-operated valve. Because my unit is NOT the stock one, it runs on a vacuum operated valve up front under the hood, aka, the "valve-like" thing.

4) Vents Not Working - heat now blows through all floor, dash and defrost vents correctly. I think the vacuum operated motor was sticking, at first. Or that I was testing the vents on MAX AC, which seems blow only through the dash vents by design.

Thanks everyone. Really appreciate all your help.

 

glad ya got it worked out

 

Did you ever find the actual name or part no. For the "valve-like thing"?

 

It is called a "Heater Control Valve."