[urq] another A/C - ventilation question

[Buchholz, Steven]

The way the '83 urq works in A/C mode is that it is always in recirculate mode ... i.e. whenever you have the temp control slider on the blue side of the control range the A/C is turned on and the intake/recirc valve (above the front passenger footwell) is set to draw air from inside the cabin and cool it.  

It is a vacuum controlled situation (well, the switch on the dash control is electrical, but it actuates a vacuum switch which flips the door.  I would imagine that if you were driving with no manifold vacuum for a long time that the reservoir would become depleted and you might see the door switch to outside air.  

The other thing that can happen is the check valve in the line to the reservoir can fail which would allow boost to get to the system ... but if that happened you'd notice the diff locks switching as well.  

... perhaps your comments about the behavior after the temps cooled might be pointing more toward a failure of the control switch ... 

Well ... I don't know how helpful this is overall, but I hope you find some value!

Steve B
San José, CA (USA)
> 
> First, thanks to those that provided advice on my burning wiring smell... the
> advice led to a good fix.
> 
> The new questions...
> Yesterday, I took off on my first trip in this "new to me" '83... driving from
> Denver to Gardiner, Montana.  It was about 100 degrees out while blasting
> along at quite a clip... A/C on full blast.  The problem... while driving
> along, suddenly the vents will switch from nice cold air, to hot outside air.
> After a while, it became clear to me that if I simply lifted on the throttle,
> the vent would switch back to A/C.
> 
> After outside temps cooled, I was no longer using the A/C.  Using the vents
> for outside air, it soon became clear that they were switching sources as
> well... going from a nice heavy stream of outside air, to none at all.  On the
> fresh air ventilation side, however, I couldn't draw any correlation between
> throttle position, and air source through the vents.
> 
> My thoughts... clearly, the position of the flap in the air plenum is vacuum
> controlled.  I believe a vacuum is required to keep the flap in the "A/C"
> position (probably recirculation)... and for whatever reason, that vacuum is
> not maintained.  The loss of vacuum results in the flap switching to fresh
> air.  When I let off the throttle, I get the vacuum back, and it switches back
> to A/C.
> 
> So... any insight on how this works/should work?  There must be a check
> valve... where?  I assume I should check the diaphragm that moves the flap...
> and any plumbing.
> 
> Any BTDT's greatly appreciated.
> 
> Dave
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