I just bought an 87 sdl and have some issues. heater would work fine then go cold. Fan would hardly work) next morning fan worked fined heat worked good. However next trip I could feel it getting colder and colder. I changed the monovalve and next long trip heat and blower fan worked ok (going to replace the blower fan---it chirps) However I can't get air to come out the defrost vents or rear seat vent (the one between the front seats) Anyone had any experience with this? Any ideas?

no hot air from the defrost vents is likely a pod problem, but there is not supposed to be heat from the vent between the seats in the back... it's a vent only. close it in the winter time.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

There is just a very small amount from the defrost vents when the buttons are set to "economy"...........normal heating mode.

Press the defrost button (all the way on the left) and see what it does.

Thanks for the reply. Even when I push the defrost button to the left no air out of the defrost vent

On my 91 sdl there is a flat inline fuse just back or side of the fuse panel, it contains a 30 amp fuse. The fuse has not blown, just corroded over time and increased resistance in the circuit. It will make the fan intermittent. Replace it.

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I LOVE CATS....AND FRIES

1981 300sd
1983 300sd
1985 300d
1983 300cd
1991 350sdl

From the intermittent perspective, it sounds like a pushbutton controller problem. The internal circuit boards are arranged in an "H" pattern with solder joints along the edges. Over time these solder joints develop hairline cracks and give you very intermittent problems.

If you do an "advanced" search for "pushbutton controller" and "resoldering" you should find serveral threads concerning this and likely some photos as well.

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Sam

84 300SD 350K+ miles ( Blue Belle )

I never thought it could be the fuse because a fuse either allows current flow or it doesn't. That is not so. My fuse was corroded and very brittle and week from age and the elements. It would allow the fan to work until heat built up across the fuse and the fan would shut off for no reason. It would not blow the fuse, it would build resistance to the point where it would no longer allow proper 12vdc to the fan. Check it, its a cheap fix.

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I LOVE CATS....AND FRIES

1981 300sd
1983 300sd
1985 300d
1983 300cd
1991 350sdl