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Heat/Vacuum problems 1986 765 700 1986

posted by  AaronF on  Thu Jul 6 12:55 CST 2006
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last visit: Tue Apr 13 12:14 CST 2010
[RELATED]

Hello,

86 765 with Automatic Climate Control. New car to me.

Was wondering if there are differences between the 1986 760 and later years regarding the vacuum and heating/ventilation systems. This is the first 700 I've owned - used to 200 series.

Anyway, The heating/AC system wasn't blowing any heat. I found a hose to nowhere - leading from the top of the intake manifold, to a tee fitting. Off of this fitting was the white vacuum line to the ACC. The other tee opening led to another tee, one leading to a diaphragm on what looks like a vacuum pump and the other end leading nowhere. It looks like it should plug into another hose that's off the same vacuum pump (but not the diaphram), but it's a different diameter hose.

Plugging the end of the hose off the intake restores vacuum and heat - but the heat won't shut off no matter what the control panel temp is selected to. No low fan speed, either - full blast on defrost or nothing. I don't hear any leaks around the vacuum lines under the dash (like near the diaphragms by the gas pedal). Plugging the hose into what I think is the vacuum pump hose has no effect, but the pump never appears to be operating anyway.

I've looked in Haynes, these posts and the FAQ. The Haynes doesn't list any vacuum pump, aside for the brakes which I don't think is on this car, or the cruise. I can't find any vacuum reservoir anywhere (under dash, front bumper or near the tranny), and don't see it in Haynes either. I also can't find any check valves. I know what they look like because I've seen them on my 240 or 260. AND, the heater valve doesn't have an arrow, like I see is mentioned in the faq.

Any ideas?

Thanks
Aaron
--
79 265 B28 BW55, 74 142, Mom's 80 262c (B21 conversion) M46, and 77 264 B28






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