- Sat Jan 16, 2021 9:20 pm
- have any mods been done to the HVAC system to change default behavior?
- is the behavior independent of engine load? Or, does it work at idle but not under load when driving?
I ask because at least a few folks living in hot climates have mod'd the system to close the heater valve when there's no manifold vacuum. So, we need to know if the default behavior should or should not apply.
And, the VCB kit is a variable since the notion of 'manifold vacuum' isn't stock anymore.
If the behavior is load dependent - works at idle but not under load, then we start at the blue/black vacuum check valve at the brake booster.
If the answers are no and no, then troubleshooting probably starts at the heater valve.
Off the top of my head... I'd first check vacuum behavior at the valve.
- Engine off, disconnect vacuum hose to valve while carefully listening. You should not hear any sign of a 'hiss'.
- Ignition on, slider at full hot; Use hand pump to verify that hose does NOT hold vacuum with engine off.
- Assuming hand pump has gauge, connect pump, start engine with slider at full hot: gauge should show no vacuum.
- Slide gauge to full cold. Gauge should show manifold vacuum.
If vacuum behavior is correct then heater valve is unable to open.
If vacuum behavior is incorrect then we have to go deeper.
Obviously you'll have to remove the intake charge tube for the VCB kit to get to the valve's hose. If it won't idle w/o the tube might want to add an extension to the line to make it easier to do the vacuum tests.
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