What do the Vacuum Solenoids Do?

[TomoHawk]

OK, thanks. I'm sure that a previous owner had the a/c pump & piping removed, but left the evaporator and servos for me to deal with. that evaporator will be a real bugger to get out without removing the whole dash. I ruled out the sawzall because the stroke was too long.

My plan was to remove the solenoids, then run the vacuum hose either through the vacuum bottle, or straight to the heater. It was suggested earlier to keep the vacuum bottle to smooth out any pulsations, but maybe I could move that bottle inside or elsewhere ( to make room under the hood) and plump it accordingly.

I appreciate your cooperation on this one. My ignorance as to the design and function of the vacuum solenoids alone made their function in the HVAC system unknown. I'll cut one to up see what's inside.

I'm sure there will be others that will benefit from this discussion.

Cheers!

[Zedrally]

May I suggest that you keep the bottle, it acts more as a vacuum reservoir and will be benefical when [if] changing heater modes.

The solenoids are just that an air switch, I have a diagram at home, and am trying to remember the logic of it all! [one opens & the other closes, fan goes 1 speed higher than the switch allows]

Even for those with A/c they can be confusing.

FWIW, Nissan should have been able to design something simpler for the A/c unit.

[TomoHawk]

Sound reasoning, mate. If the vacuum bottle were missing, you'd probably have serious lag when changing the heaster functions.

BTW, I have the "Fast Frog" vacuum diagram.

Click here for Fast Frog HVAC diagram

I understand what you mean by fan speed. For some reason, When you set the lever to a/C, the fan goes faster (on high speed), than the vent setting.. My diagram must be missing something critical. Unfortunately, it doesn't show the vacuum flow direction, or the arrows don't make sense.

cheers

[Alan Pugh]

The PO must have cut the wires off the two solenoids.

Each solenoid has a blue and black wire coming from it to a four pin connector.

[TomoHawk]

Do these electrical solenoids fail in the open position? There shouldn't be any reason to cut the wires off.