I am trying to find any/all potential vacuum leaks in my truck, (2005 Expy) and I have isolated the little vacuum line that goes through the firewall, over behind the battery, as a possible leak. This line goes through the firewall, inside the cabin and returns back outside to the engine and seems to operate the hot water control valve. All of the other vacuum lines I can find seem to hold vacuum really well, but this line seems to have a large enough leak my hand pump can't create a vacuum. I think it is leaking somewhere in the cabin.

The climate control system seems to work okay, nothing at least I have picked up on yet...no temp problems, no air flow issues.

So I'm trying to figure out if anyone out there knows if the digital dual zone climate control system uses vacuum for anything, and if so how it uses it.

Thanks for any help.

 

Vacuum is used to control all the doors that move to direct the inlet and outlet air flow.

The EATC uses solenoids to switch the supply vacuum to the appropriate door vacuum motors based on the airflow selections of the operator. The o-rings in the solenoids do tend to fail and to leak, causing a loss of control of the airflow.

The vacuum line that goes to the coolant valve is only active when the system is in MAX ac mode. The valve closes off heater core low so that a hot heater core doesn't contribute to reheating of conditioned air.

 

SHO89,
Thanks for the information. I really wasn't sure how the vacuum and digital systems worked, (or didn't work) together.

Any idea if the vacuum part of the system should be air tight? In other words I've noticed that I have what appears to be a pretty good sized vacuum leak... unless the system is supposed to "vent" vacuum under certain conditions. If I isolate the line going into the firewall and out of the firewall.. I can't seem to pull a vacuum on them.

Man I hate chasing vacuum leaks...

Thanks again.

 

You would need to either remove the EATC/DATC control head and cap off the black vacuum supply line or find the connector within the vacuum harness and cap it there to isolate the system. Otherwise it is impossible to pull a vacuum because of the routing to allow vacuum even if the system is turned off.

Are you having any issues of airflow from defrost?

If not, there may not be anything wrong with your system.

Low/No vacuum supplied to control head should cause the default operation, which is no vacuum applied, and result in airflow from defrost only.

Hope this helps, and keep us updated

 

MasterTech,
That's what's puzzling me, I can't seem to get the HVAC system to act like it is a "closed" or isolated loop, in a vacuum kind of way. I have isolated the inlet and the outlet vacuum lines for the HVAC system... they are located behind the battery and run through the firewall. The outlet only seems to operate the water control valve on top of the passenger side valve cover, so that was easy to isolate.

As far as I know the HVAC system seems to work okay... although some ideas on how to verify that may help. I did check the EATC and found no trouble codes on it. My system doesn't have a floor setting, but the defrost setting works when checking codes, (found that out from the F250 superduty guys).

I am chasing what I think is a vacuum leak and found a couple of hoses in really bad shape behind the battery, (between the battery and firewall). They were deteriorated really bad. Replaced them and so as I was confirming how airtight the systems is, I found the inlet/outlet through the firewall. I isolated them and could not pull a vacuum on that part of the system. I could not find a way short of pulling the dash out to figure out if I have a suspect HVAC system, or if they all act that way. So I thought I would ask around and try to find out.

Thoughts?

Thanks.

 

Well I couldn't get the HVAC system to hold any kind of vacuum, so after playing with it for a few days I hooked the vacuum line back up to the T behind the battery box. Should have guessed this one. Now air only flows out of the defrost vents. The air seems to be pretty cold, which is good cause it is still hot here, but the only place it will come out is the defrosters! Dang it.

Guess the system was "stuck" on the dash vents, but when I removed the vacuum line, it must have allowed the system to go back to the default position of defrost.

Any words of advise before I remove the dash and start changing out the vacuum motors?

Thanks guys.

 

FYI.

I don't know if it will work on these trucks but I used to check vacuum actuators by taking the hose off of the them, then pushing them closed and then putting my finger over the air inlet and then releasing the actuator. A good one will stay closed or will open slowly but a leaking one will open quickly (perhaps 2 to 3 seconds).

Also I've fixed small tears in the diaphragm by putting a thin layer of RTV over the tear and letting it cure. But usually the outside can is crimped together so you have to work the crimp out to open it and then crimp it back together with a hammer and a small anvil.

Let us know what you find.

 

joe51,

Thanks for the information. I remember fixing old rubber diaphragm fuel pumps that way too!!! How cool that was, to be able to repair something using simple hand tools.

Anyhow, I got to checking the system again because it just didn't set right with me that the system would allow air to flow where it was supposed to, (even if I have some leaks in the system), before I started checking all of the vacuum lines behind the battery box... AND you guessed it, one of the check valves was backwards. Go figure. I must have switched it when I was replacing all of the lines that were falling apart.

So I put the valve back in the correct way and the HVAC system operates like it is supposed to. It may still have some vacuum leaks in one or more of the vacuum motors, but it at least routes the air where it is supposed to. So now I can get back to figuring out if the vehicle's entire vacuum system is as air tight as it is supposed to be.

Thanks everyone for your advice and help.