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Help identifying what this is for - Air pump

December 11, 2021, 03:44:30 pm

Hey does anyone know what this pump is for? The small black airlines that come off the bulb-looking thing are broken and I can't seem to figure out where they are supposed to go? This is located in the front panel access area of my 1995 U300.

Thanks in advance!

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Re: Help identifying what this is for - Air pump

Reply #1 – December 11, 2021, 03:55:40 pm

That's a vacuum pump for the dash heat and a/c.  The round thing is a vacuum reservoir.
It should run periodically when the ignition is on.  When enough vacuum is attained a vacuum switch will shut it off until the vacuum level gets too low again.

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Re: Help identifying what this is for - Air pump

Reply #2 – December 11, 2021, 03:59:52 pm

Any chance you know how this should be routed? The small vacuum lines have disintegrated and I have no idea where they originally ran to.

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Re: Help identifying what this is for - Air pump

Reply #3 – December 11, 2021, 04:47:39 pm

See if the photos below help any.  Routing is basically out from pump, into reservoir, and out of reservoir to a "T".  From the "T" one line goes to vacuum switch - the other line goes up to dashboard A/C-heater control panel.  The vacuum switch controls the relay that turns power ON and OFF to pump.

BE CAREFUL MESSING WITH THE VACUUM SWITCH.  If you break it, a replacement is very hard to find.

NOTE:  Pencil drawing - wiring corrected

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Re: Help identifying what this is for - Air pump

Reply #4 – December 11, 2021, 05:15:21 pm

The vacuum pressure switch controls a relay mounted on the firewall nearby.  The relay gets power from a fuse under the lift-up dash cover.  The relay sends power to the vacuum pump.  The ignition switch must be ON for pump (fuse) to receive power.

See B-2037 12V Wiring Diagram.

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