i've been looking through lots of posts about bypassing the servo but can't find this answer. i was wondering what would happen if i did it in the most simple way, just connecting the hoses on either side of the servo to each other, with no valve or anything.

just got a 1980 300d to replace my 1978 that got in a fender bender. servo is leaking severely and want to at least do a quick fix so i can get this thing moving.

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1980 300D, 128K

You will have to install some sort of manual valve, unless you want heat all the time. The servo is, in a sense, an insanely complicated heater control valve.

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

x2 Just roll the window down to cool you off

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$60 OM617 Blank Exhaust Flanges
$110 OM606 Blank Exhaust Flanges
No merc at the moment

so the heat will be on all the time! that doesn't sound so great. maybe i need to put some valve in. then i can at least turn it off in the summer, even if i can't control it from inside.

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1980 300D, 128K

You can always switch the servo from the 78 to the 80 if it is working.

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I currently have mine bypassed while I send my leaking servo out for repair. I have a ball valve in line that I open or close depending on the temperature for a given day.

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Joe

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1980 300SD - 495k miles - 'The Ambassador'
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Former Family Members
95 C280
73 280SEL
90 300D
87 300SDL (X2)
86 560SEL
84 300D
80 300SD

You can buy a manual ball valve for 5/8" heater hoses, which should work (recall seeing on A Body Mopar Forum - Home of Vintage Mopars like the Dodge Dart and Plymouth Barracuda). If more ambitious, you could rig a cable-operated valve for a 60-70's U.S. car, but a lot of hassle.

I think your best bet is to swap in a manual system from a 240d - I did that on my '80 model coupe and I'm very pleased - goes right in and looks like it belongs there. If the car is your DD you can even keep driving it during the transplant - I drove the coupe a few times for grins with the dash and the console out, the guage cluster held in place (sort of) with a coat hanger, wires everywhere - quite a sight. The job really wasn't too hard I look for D Morrison's writeup with great pics on how to get the a/c evaporator out. By the way, while you're in there, be sure to test the heater coil - my "new" one (from the 240d) leaks a little - would have been so easy to fix when I had it all apart.

Here is a good thread on a bypass of the servo.

If you are pressed for time you can leave out the cable + cable-actuated valve and just put in a ball valve.

early W123 servo bypass described/pics

Kudos to unkl300d for the excellent writeup on that.

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

so i just did a straight bypass because i wanted to get it done fast. i think i'll add a valve later -- or put in the servo from my other car. that servo sort of worked - i could turn on heat and it would be very hot but couldn't control temp, so i had to keep switching it on and off. and ac didn't work, not sure if that's why. it didn't leak though. and there's a chance it was banged in the accident. hmm. probably shouldn't use that one.

i take it there will be no chance of a/c with no servo? i have the service records for this car and it was recharged at some point in the past 10 years. would be nice but not totally necessary.

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1980 300D, 128K

You don't need the servo in circuit for the AC to work but you will need a way to shut of flow to the heater core such as the aforementioned valve.

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Joe

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1980 300SD - 495k miles - 'The Ambassador'
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Former Family Members
95 C280
73 280SEL
90 300D
87 300SDL (X2)
86 560SEL
84 300D
80 300SD

I think is the amplfier is bad, the ac will not work.

You may want to read up on it, in this manual....it is quite interesting...

1971 Chrysler Imperial Auto-Temp 2 Service Reference Guide - Session 281

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