Stuck on defrost

Couple questions, reference the pictures attached, so I can finish.

1. What are the two . . .valves/manifolds on the firewall?
2. Is this a spare vacuum line installed in the harness?
3. Where is the reservoir and check valve?
4. Which vacuum line supplies vacuum to the Temperature blend door? I see electrical wires behind the knob.

Solenoids not associated with the heating and cooling then. Been looking through my Haynes manual and there is no mention of the vacuum reservoir. Is it under the battery? How big is it?

Get back to you next week

Tested the lines by removing the vacuum harness and suppying vacuum individually and found the following:

#3 Black Able to supply vacuum and it held for 1 minute without loss. Released vacuum and hooked up again, then started truck and vacuum supplied by engine measured approximately 21 inches.(Gauge not calibrated)

#1 White Able to supply vacuum and it held for 1 minute without loss. Ran system and supplied vacuum and fan speed increased indicating recirculate door had closed.

#2 Yellow Able to supply vacuum and it held for 1 minute without loss.

#5 Blue Able to supply vacuum and it held for 1 minute without loss.

#6 Red Able to supply vacuum and it held for 1 minute without loss. Ran system in defrost mode and supplied vacuum. Air switched from Defrost to Panel.

Another question. Is the temperature blend door Electrically controlled and vacuum actuated? Diagram shows a full vacuum position but doesn't show a vacuum source to it. Temp switch has 3 wires coming out of the back.

Going back in today and check vacuum under load while driving to verify drop of vacuum pressure and see how much. Will also try adding vacuum to blue and yellow lines to see what results are.

Found the reservoir and check valve. Fitting going to line running from check valve to reservoir appears to have had a small crack at the valve (it broke off when looking at it and one side seemed dirty indicating sucking air for a while.). New one on order. Will arrive tomorrow. Go ahead and let me know how to test blend door

Everything under the hood has been reinstalled. Problem still exists. Did not replace the reservoir tank but did test it. 20" vacuum from tester held for 1 hour. Know there has to be a leak somewhere. Do you know what line provides vacuum to the blend door?

Yes need to test it. The reason I asked about the vacuum line was because the diagram shows the door in the full hot position as being with full vacuum. Hence the previous question re is it electrically controlled and vacuum actuated

15 Amp fuse OK. Power to the blue w/pink stripe wire when power on. The switch behind my temp control knob has 3 terminals. Tested resistance on terminals 2 & 3 with Digital ohm meter set at 20K. Full hot shows.300. Full Cold shows 4.50. Replace the switch?

Replaced the potentiometer. Had different readings than the old one. Have more heat now but still not what it used to be. How much trouble to change the actuator? By the way, the new checkvalve fixed the problem of distributing air to the defrost when going up hills. Or could there be a partial blockage in the heater core?

Hi, I have a similar problem I think.

When I am driving, there is a hiss coming from the dash around the heater control area, when I come to a stop, it goes away, and is not there when I idle. I find I have less power while driving, and again, seems fine while idling. I looked under the hood, and as far as I can see, from pictures I have found on the forums, everything is connected.
Before I take apart the dash, is there another way of diagnosing it?

I could get a replacement heater control from the wreckers for $50, which could be an easy job, if that is the quickest solution.

Kevin