HVAC questions

[pizzaman09]

I have a 90 Comanche with the 4.0L.  I have two HVAC questions.

1. When I accelerate and engine vacuum dips, the ventilation switches from blowing out of the vents to defrost mode.  As soon as I let back off the throttle it returns to the correct level.

 

2.  On cold days when driving, very cold air rushes into the the passenger foot well.  Both of my Comanches did this.

 

Any thoughts on how to solve these problems?

 

[jdog]

How's the vacuum ball in the front bumper?

You've got leaking firewall to heater box seal or fresh air vent seal

 

[pizzaman09]

9 hours ago, jdog said:

How's the vacuum ball in the front bumper?

You've got leaking firewall to heater box seal or fresh air vent seal

 

Is the fresh air seal the flap that is in the passenger foot well that is actuated by vacuum?

[jdog]

There's a seal around the air box that seals the heater and the fresh air vent. Fresh air comes thru it and runs across the heater then is distributed thru out the truck, if the seal is worn it will let air leak past and into the cabin

[cruiser54]

[pizzaman09]

It would appear that the culprit was a lack of vacuum check valve for the heater.  The only fitting in the line was a brass barbed fitting in the manifold. Does anyone know what the part number is for the factory fitting or should I just get a generic inline doorman check valve.