I'm trying to diagnose the HVAC system in W116 chassis 1980 300SD. No heat in cabin, A/C compressor only comes on when DEF button is pressed. I have CD manual but most of the climate control stuff is greek to me...any sources for HVAC testing procedures? I have basic tools, like a hand vac pump and a multimeter.

Thanks,

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1978 300SD 149K miles silver-blue "Maxine" (mine!)
1979 300SD 318K miles red "Helga" (SOLD)
1980 300SD 321K miles yellow "Linda" (younger daughter's)
1980 300SD 148K miles blue (SOLD)
1980 300SD 153K miles green(parts car, SOLD)
Yes, I have a W116 fetish :-)

Yes, the servo is new-ish, but how do I test the amp?

__________________
1978 300SD 149K miles silver-blue "Maxine" (mine!)
1979 300SD 318K miles red "Helga" (SOLD)
1980 300SD 321K miles yellow "Linda" (younger daughter's)
1980 300SD 148K miles blue (SOLD)
1980 300SD 153K miles green(parts car, SOLD)
Yes, I have a W116 fetish :-)

Larry Bible faxed me some diagnostic info that was very helpful in fixing the climate control issues with my 1977 300D. It covers both early systems, up to 1980, and later systems, from 1981. In the sprit of passing on the good work of Larry, shoot me your fax number and I'll fax it to you. I have it in the office today and am faxing it to someone else, so you can have it by this PM

JCD

My fax number: 512-239-6050

Thanks!

-=-=-=Ed Block

__________________
1978 300SD 149K miles silver-blue "Maxine" (mine!)
1979 300SD 318K miles red "Helga" (SOLD)
1980 300SD 321K miles yellow "Linda" (younger daughter's)
1980 300SD 148K miles blue (SOLD)
1980 300SD 153K miles green(parts car, SOLD)
Yes, I have a W116 fetish :-)

JCD

I owe you one--need any W116 parts? ;-)

-=-=-=Ed Block

__________________
1978 300SD 149K miles silver-blue "Maxine" (mine!)
1979 300SD 318K miles red "Helga" (SOLD)
1980 300SD 321K miles yellow "Linda" (younger daughter's)
1980 300SD 148K miles blue (SOLD)
1980 300SD 153K miles green(parts car, SOLD)
Yes, I have a W116 fetish :-)

Thanks for the offer. Good luck and try not to spend too much time under the dashboard.

JCD

The blower in my 300SD will not come on unless the AC switch is in the ON position.
So, when I want heat I have to put the AC switch on. Once the blower is on I can turn the switch back off and the climate control will continue to function normally. At least I think it's normal (ie: blower speed will vary as the interior temp warms to the thermostat setting).
Also, the blower will run (with AC in the OFF position) when the climate control is in the Bi-level position. However the air temp doesn't seem to be very warm even if the thermostat is cranked all the way up.
Does this sound like normal operation to you guys?

Joe

__________________
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

There is a vacuum switch that controls the on-off functioning of the entire system. It is supplied with vacuum from the intake manifold via a thermoswitch located on the bottom of the servo (or is it the servo bracket – memory’s going…). If the main switch does not receive vacuum, the system blower will not turn on. This is likely to be your problem.

OR you could have a large enough vacuum leak from elsewhere in the system which will not allow enough vacuum to develop to operate some/any of the vacuum switches. Whip out the vacuum pump and test every diaphragm in the system. If they are all good, check the vacuum switches directly – current should flow (continuity) when vacuum is applied..

Good Luck.

RTH

EdBlock - You got it fixed?

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... Kerry

126 tailed by a 203, 129 leading the pack.

Spent some time troubleshooting yesterday afternoon, thanks to some excellent info from JCD. I think that I have both an electrical problem (resistance circuit--probably the amp and/or the ambient temp sensor) and a vacuum problem (center vents won't open, etc...)

Unfortunately while testing vacuum I tore the rubber on one of the "ports" of the vacuum lines-to-servo connector plug...anyone had luck repairing with silicone or should I go through the pain of replacing the rubber plug (how in the world do I get all those vacuum lines off the little brass barbs?) I have a spare rubber plug but it is also 20 yrs old--if I have to replace it, I guess I should go ahead and buy a new one, eh?

Also, anyone had any luck re-building the amp?

Thanks,
--=-=-=Ed

__________________
1978 300SD 149K miles silver-blue "Maxine" (mine!)
1979 300SD 318K miles red "Helga" (SOLD)
1980 300SD 321K miles yellow "Linda" (younger daughter's)
1980 300SD 148K miles blue (SOLD)
1980 300SD 153K miles green(parts car, SOLD)
Yes, I have a W116 fetish :-)

Well, I substituted another CC amp and still have the same prob--so the sub might be bad, too,I guess...both had dark "hot" marks on the PCB under a big resistor.
Perhaps I'll try replacing that resistor on one of them and see what happens.

Also while crawling around under the dash I heard what sounded like an arc-ing sound...turned out to be the top one of three relays behind the drivers side kick panel. All appear to be the same, five pins and about 1 cu in. Substituted from parts car and it made the same noise, as if cycling rapidly (1-2 times per second). What are those relays for?

Tried putting 12v directly to servo and measuring resistance (ohms) but no change...makes me think that the servo may be fried, too...it does not look original, but it doesn't seem to move. My parts car does not have a servo in it.

Still have the same symptoms: no heat (I mean none) and center cents won't open. Any more ideas out there, short of spending $500+ to buy new components?

__________________
1978 300SD 149K miles silver-blue "Maxine" (mine!)
1979 300SD 318K miles red "Helga" (SOLD)
1980 300SD 321K miles yellow "Linda" (younger daughter's)
1980 300SD 148K miles blue (SOLD)
1980 300SD 153K miles green(parts car, SOLD)
Yes, I have a W116 fetish :-)

Hey I came accross this post, and was wondering if it wouldn't be too much trouble to fax this to me? If you like I'm sure I can compensate you for the time. Let me know!

Adam

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'79 240D
'79 300SD

those that are missed:
'80 300TD bandit
'76 300D cleta jill