Adding recirculate switch for cabin air - absolute necessity

[djnolan]

I own two 944's and bless the lord they are equipped with recirculate switches for the cabin air. The switch has two purposes, in the summertime to prevent hot humid outside air from overloading your A/C, and at all other times to prevent smoggy or dusty air from coming thru the heater and defrost vents and overloading your lungs and sinuses.

My Ford Explorer did not come equipped with this feature. It has the recirculate for A/C only. In defrost or heat mode, it sucks in 100% straight outside air. When the roads have been salted and sanded in the wintertime the air can be quite dusty and can really agravate your loved ones, especially if they have a cold.

In most cars, the recirculate process is controlled by a simple "vacuum motor" that moves a flap to admit or block outside air from the vent system. It looks like a round cylinder about 2 inces accross with a vacuum line connected to one end and a metal lever connected to a flap at the other end. If a Ford or GM vehicle it will change pisitions and move the flap when going from A/C to Max A/C with the engine running. In position one the flap admits ouitside air to the vent system, and in position two the flap blocks outside air and sucks in inside air to the vent system. Listen under hood or under dash for change in air flow noise as recirculate mode is engaged/disengaged with climate control switch.

How nice if it could be made to work in heat and defrost mode too.

---------------------There has got be a fix for this-------------------------------

Parts list:
1. Electric vacuum control solenoid from some GM vehicle emission system
2. 3 ft or so of vacuum line
3. An electric switch
4. Fuse panel power adapter for adding an extra circuit

Supplemental items:
- Assorted vacuum line fittings
- Roll of wire, 18 gauge.
- Crimp on connectors
Total cost: about $40 bucks give or take

Step 1: Connect the power adapter to the fuse panel and make sure you have 12v when the engine is running and not 12v when it is off (use test lite or Volt meter to verify).

Step 2: Find a good spot on the dash to mount the electric switch(item 4) ,(or just let it hang down underneath dash for now) and run wire from fuse panel to this point.

Step 3. Locate recirculate actuator "vacuum motor" described above, usually under dash in passenger footwell and disconnect and plug vacuum line to it.

Step 4. Run supplementary vacuum line from recirculate actuator thru firewall to underhood and connect to another vacuum source. [Warning: DO NOT cut any existing vacuum lines. Find where one of the exisiting underhood vacuum lines has a connector and replace with a vacuum Tee connector to add an extra line. If you cut one of the custom factory lines you may have difficulty making a connection or restoring the original function if you decide to undo this procedure.] That said, run the line thru an existing grommet in the firewall instead or drilling new holes so as to not start rust problem.

Step 5. The vacuum solenoid (item 1) will be used to control whether vacuum is fed to the vacuum motor actuator. Mount vacuum solenoid (item 1) nearby vacuum motor and connect supplementary vacuum source to one port and connect other port to the vacuum motor port.

Step 6. Connect wire from electric switch to vacuum soleoid hot terminal, and connect 2nd vacuum solenoid electric terminal to a good ground.

Step 7. Start engine and test. With electric switch in one position air should recirculate, and in other position should supply outside air to vents. With blower on high speed listen under hood or under dash for change in air flow noise as recirculate mode is engaged/disengaged with your new switch.

This should complete the job. Suggest you do this in stages with the help of a volt meter to check for power and ground where needed. You may have to remove various dash panels to get access under dash. When the switch is on and the solenoid is energized you should get recirclated air, and when not you should get outside air to cabin.

I can post some pics if requested! Hope nobody finds this off topic.

Good Luck!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[Grandad#3]

Hi djnolan, Great write up. Your work up sounds pretty good. Pictures always help improve any new idea, and for us simple guys to copy / see where you connected / mounted stuff on the air handler. Keep up the good work.

Cheers,
Larry

[Cocacolakidd]

Under the hood, on top of the firewall is a filter attached to the intake air of the vent system - periodic cleaning or replacing this filter will clean up allot of the inside air of vehicle.

I have also made a secondary filter of my own from a HVAC household filter cut to size and placed/spaced at the original filter - This one I replace often as the OEM Porsche filter is expensive.

[djnolan]

OK. All is working well. Here are some pics. I am undecided how to mount the switch and if I should drill a hole in the dash. I did have to put a "reducer" in the vacuum line as the vent was closing too adruptly and the idle was pulsating a little. This reduced the vacuum enough to smooth out the idle and make the door vent door close smoothly.