HVAC Restoration - Troubleshooting

[Comanche Pioneer]

Hey all!

 

A few pics of my truck and parts haul for attention.

 

I recently completed both a closed-to-open cooling system conversion and a fairly comprehensive HVAC renovation on my ‘89 Comanche. Good news first: the A/C system held vacuum for over 2 hours before charging, and the air is now blowing ice cold. So mechanically and thermally, everything appears solid.

 

That said, I’m having airflow issues at the vents:

• The system only gives real airflow on BI/LEV, and even then, the floor vents dominate.

• On MAX or Normal, airflow at the dash vents is extremely weak or nearly nonexistent.

• When switching modes, I can hear the blend or mode doors moving, and the airflow sound shifts, so I know something is actuating.

• My understanding is that most mode door actuators are on the left side of the HVAC box, with the recirculation (MAX A/C) door behind the glovebox.

Given that I’m getting good cold air and door movement sounds, but almost no output on MAX or NORM, it doesn’t seem like a total vacuum failure. I’m starting to suspect the recirc door is stuck or not opening, which would restrict intake airflow, especially on MAX. The fact that BI/LEV works (albeit floor-heavy) supports that something is partially functioning but not fully moving through the correct routing.

 

Any of you run into similar issues? Does this sound like a stuck recirc door or something else deeper in the blend/mode door system? I really want to eliminate all possibilities available short of removing the dash and completely rebuilding the HVAC box.

Thanks in advance for your help!

[eaglescout526]

Have you checked the vac lines running from the firewall at the expansion and heater valves to the reservoir behind the bumper? That controls all vacuum to the vacuum motors. 

[Comanche Pioneer]

25 minutes ago, eaglescout526 said:

Have you checked the vac lines running from the firewall at the expansion and heater valves to the reservoir behind the bumper? That controls all vacuum to the vacuum motors. 

I'll end up doing a full vacuum system evaluation from the vacuum reservoir to the check valve on the engine side to be sure that's not at least causing partial problems.  Since I'm hearing airflow changes inside the cab and doors moving around, I don't suspect its a total vacuum failure.