'75 300 - How does AC blower fan get switched on? PICTURE

[1975300D]

HI Guys, wondering if anyone can tell me which vacuum lines (which color) connect to the three vacuum ports on the AC switch?

I have been trying to get the AC blower motor to turn on, but don't know how the switch even works. I know the motor is good.

Thanks

[meltedpanda]

IIRC , the vacuum lines only serve to open and close the vents
The switch rotates to turn on the fan

[Mike D]

Yes and no. The changeover switch is selected by a diaphragm. Micro switch on the left side of the center console above the accelerator pedal in a LHD vehicle.

[kraakevik]

The vacuum lines should be yellow, green and some striped combination of either color, I believe--good luck



Tim Kraakevik
kraakevik@voyager.net

[1975300D]

Thanks guys. The vacuum lines I have are all green. There are three shades of green. One I assume is the supply line, and the other two are for the vents.

But my other problem is that I can't get the AC blower motor to turn on. What mechanism turns it on? Does it have different speeds like the Heater Blower?

[1975300D]

Micro switch on the left side of the center console above the accelerator pedal in a LHD vehicle.

Mike can you please explain that again.

[whunter]

Originally Posted by 1975300D

HI Guys, wondering if anyone can tell me which vacuum lines (which color) connect to the three vacuum ports on the AC switch?

I have been trying to get the AC blower motor to turn on, but don't know how the switch even works. I know the motor is good.

Thanks

The knob (valve) supplies vacuum to an element that moves the blower switch on/off.

***********************

Above to the right of the driver accelerator pedal area is where the blower switch and vacuum element are located.



Here is the vacuum element and blower on/off switch.













Switch
MB# 1158211851
Pelican Parts - Automotive Parts and Accessories - Porsche & BMW

There are two vacuum elements in this climate control.

vacuum element
MB# 0008001775
Pelican Parts - Automotive Parts and Accessories - Porsche & BMW

vacuum element
MB# 0008001175
Pelican Parts - Automotive Parts and Accessories - Porsche & BMW


.

[Mark DiSilvestro]

In addition to the AC compressor circuit, the AC knob also operates a vacuum switch that controls a vacuum-motor on the left side of the heater box, above the accelerator pedal.
The vacuum motor works a flap that diverts airflow based on whether the AC knob is set to AC or OFF. That vacuum-motor also controls a change-over switch that connects your heater-blower when the AC is OFF, or the AC blower when the AC is ON. Either blower works off the same fan-knob in the heater control-panel. The change-over switch simply changes the connection from heater-blower to AC-blower, depending on how the AC knob is set.

First, does your heater-blower work. If it does, that's a good sign that the fan-switch will eventually be able to operate the AC blower, once you get those vacuum-lines hooked-up.
With the engine running, first make sure one of the three vacuum lines is getting vacuum. If it is, then connect the three lines to the ports on your AC control. If you didn't unhook the lines or remember how they were connected, this may take some trial & error to figure out the right hookup. (Possibly, the vacuum supply line connects to the center-port on the AC control)
Then with the engine running, you need to watch the vacuum-motor linkage above the accelerator pedal, to see if it moves up and down depending on where you turn the AC knob.
All this has to operate before your AC-blower will work.

Happy Motoring, Mark

[Mike D]

Through the magic of my mental prowess I'll induce Roy to post pictures of the switch and diaphragm. Omminy-ominny-walla-woop!

Thanks Roy!

[1975300D]

THanks Hunter for those pics! That is what I needed for my other thread about that device. I couldn't figure out how it went because the brass colored bracket that holds it came off the box so I had no idea how the whole thing was fastened to the wall. (I ended up JB welding the brass plate back on)

Although, I do not have that white thingy device with the brown vacuum lines that you show in your first photo. What is that?


Thanks Mark, I will do what you suggest to test which vacuum ports do what. I have already manually activated this switch with the HEATER blower running, and it does shut off the HEATER blower. However, it does not activate the AC blower. So maybe I have corroded pin contacts, at least the ones that send power to the AC blower.

[whunter]

Originally Posted by 1975300D

THanks Hunter for those pics! That is what I needed for my other thread about that device. I couldn't figure out how it went because the brass colored bracket that holds it came off the box so I had no idea how the whole thing was fastened to the wall. (I ended up JB welding the brass plate back on)

Although, I do not have that white thingy device with the brown vacuum lines that you show in your first photo. What is that?


Thanks Mark, I will do what you suggest to test which vacuum ports do what. I have already manually activated this switch with the HEATER blower running, and it does shut off the HEATER blower. However, it does not activate the AC blower. So maybe I have corroded pin contacts, at least the ones that send power to the AC blower.

You are welcome.

Look here for the answer.
Welcome to the fleet 1976 W115.114 "300D" dark Green

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[whunter]

Originally Posted by Mike D

Through the magic of my mental prowess I'll induce Roy to post pictures of the switch and diaphragm. Omminy-ominny-walla-woop!

Thanks Roy!

Chuckle..

You are welcome.

.

[1975300D]

Thanks Roy. (I assume you are Roy?)

Did you do that work around because the vacuum leak was in the ignition switch module and that was easier/cheaper than changing the ignition switch?

I have a delayed engine stop as well. About 1-2 seconds.

[whunter]

Originally Posted by 1975300D

Thanks Roy. (I assume you are Roy?)

Did you do that work around because the vacuum leak was in the ignition switch module and that was easier/cheaper than changing the ignition switch?

I have a delayed engine stop as well. About 1-2 seconds.

The key switch vacuum valve failed (leaking).
When the failure happened it was winter = no blower vacuum = no heat.
I capped it for a day, but using the manual lever was a pain, and this works fine.
It is on my list for repair soon.

.

[huffandpuff]

parking brake marginally holds vechile is there a way to adjust to hold better??