No air from the front-vents when engine is hot

[Meridivs]

These super-hot days our TS had started to develop a very strange problem:
- when you first start the engine the A/C works normally and cold air blows from the front vents on A/C or MAX as usual
- if we shut-down the engine and try to engage A/C or MAX again the cold air would only come-out through the top (windshield) and low vents - no more front ventilation
- all solenoids appear to be working (moving)

Had any of you dealt with this problem on this car?

[sajo6000]

I have the same problem and everything works as it should for me too, it's probably a design error.

Regards
//Stocken

[LMP]

With time, mine became susceptible to vacuum loss. Air at low vents is the "default" value, that is when no vacuum is applied. Vacuum is needed to pull the vacuum bellows for top openings. When I go uphill and more throttle is used, it happens I loose the top vents and it reverts to bottom. As the road levels and throttle is released, vacuum comes back and air returns to top.
As my place rarely comes "very warm" I cannot comment on that factor by experience...but remember very warm air is less dense and can require more throttle for same power...thus impacting on available vacuum.
I should check out ALL vacuum tubing , incluiding power brake and cruise control (by the way, my cruise control lacks action too...I need to help a little going uphill, same cause).

[Meridivs]

Thank you for the replies, very interesting point LMP - you're a true engineer inside and out, I'm glad you have a Trans-Sport

I will throughly check the vacuum on this car and report any findings.

Strange thing - I opened the dash and looked at the vacuum-powered solenoids that control the air-flow. All seem to operate correctly when called-for but maybe there's something that I overlooked.

Do you have any idea which solenoid controls the front/middle vents?

[LMP]

Originally Posted by Meridivs

.... which solenoid controls the front/middle vents?

Well make sure we address "solenoids" and "bellows"

Electrically controlled solenoids , that deliver vacuum to bellows, are labelled 1 to 5...in the electrical diagram..but I do not know if this also relates to their actual position on the vacuum rail under the glove box...but they can be identified by the color of the tubing.


solenoid #3 is energized on positions MAX/HI-LO/VENT . It controls bellows/valve (blu tubing) for windshield defrost outlets. This bellows is spring return . ENergized position SHUTS the def outlets. release position (sol 3 not energized) ) is to defrost.

solenoid #1 (energized on HTR...to red tubing) and #5 (energized on MAX VENT DEF to yel tubing) both control floor valve bellows. This bellows is vacuum positioned (no spring return)
Sol 1 deflects bellows to full floor (but some air is left to DEF) ,
sol 5 energized on MAX VENT DEF deflects bellows to "shut" floor to allow "all" air to DEF...but some air is left to floor.

solenoid #2 (energized on MAX , HI-LO, VENT , to brn tubing) controls panel outlets bellows/valve. This bellows is spring return .Unactivated position is CLOSED.

solenoid 4 (energized on MAX or RECIRC depending on labeling, to orng tubing) controls outside/recirc. bellows/valve. This bellows is spring return . Released position is outside air.

on POSITION htr/def , NO SOLENOID IS ENERGIZED: this is , in fact like the DEFAULT position ..all bellows realeased: vent valve is closed, DEF valve is opened, air is from OUTSIDE, floor is opened.

THe TEMPERATURE control is totally electrical.

(NOtice also my book says solenoids 2,3,5 to be energized on the A/C position (which would kill the DEF and floor outlets)...but this is proved wrong by the fact that ALL other heater position can be used simultaneously with A/C... THis comment applies with pushbutton controls...not sure what happens with rotary controls that show on my diagram..though my '93 is actually push button..)

EDit: just found I had that already on my website
www.avigex.ca/xport/hvac_delivery.jpg