I am having a bit of trouble finding the issue here. When I turn my heat on, no matter what vent setting, it will only come through the defrost vent. Has anyone else had this problem? Any pointers or tips? Also does anyone have a vacuum circuit diagram of the heat/ AC controls?
If you have a leak in a vacuum line then the system will default to demister vents. The number one cause of vacuum leaks is where the vacuum line passes through the bulkhead on the passenger side (LHD vehicles).
'96 ZJ 4L auto, '95 XJ 4L manual, 2003 Landrover Discovery
In the UK: 1969 MGC GT
Well I still haven't figured it out. All the lines seem good passing through the firewall. I'm determined to find the culprit, time for troubleshooting is not easy to find. Does anyone know anything about the strange box underneath the battery? How do I test the vaccuum diaphragm for failure?
Most of these problems are vacuum leaks under the hood.
One hose on the reservoir. Disconnect the hose, is there vacuum on it? Plug it, see if your heater controls work.
Removing the panel looks something like this 94 pic. Vacuum lines are larger colored in the center. Black vacuum line disappearing into the shadows is the supply line which runs out through the firewall to the tee fitting, then to the vacuum reservoir.
If you need to remove the control panel, do not disconnect the lines from the panel. There's a quick-disconnect plug, make sure it's fully seated. Mine came from the factory with one side not clipped.
So I still can't find this leak... I took the hose off the reservoir cut off an inch and it fit snug and good but for good measure I left it off and tested to see if the reservoir was leaking but I had no vacuum in the lines...
What could this mean?
I took apart the bottom half of my dash and couldn't find a leak there either. But when I took the controls out the knob wasn't seated right on the inside so I fixed that thinking that was my problem and sadly no it wasn't.
So any suggestions would help at this point...
And another question is there any electrical things at all the could cause this or fuses or stuff like that I should check?
Not sure a vacuum leak would blow bubbles since the air goes into the leaky line...
Look for a broken/missing/disconnected vacuum line. Only runs a few places... from the vacuum reservoir to speed control servo, firewall tee fitting, and intake manifold connection (vacuum source). Start at the intake end, there's vacuum there with the engine running.