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  #1  
Old 03-30-2010, 10:45 PM
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'79 300D >> Heat has diminished recently?....

Hello,

When I first got my 300D/W123 (used), it seemed like the heat worked pretty well, even at normal streets speeds in the 30's. It worked really well up at highway speeds, producing a decent amount of heat for the cold northwest winters.

Recently however it seems like my heat has diminished and hardly even works at street speeds. I have to really be cruising at highway speed for a while to feel any heat at my vents.

I've heard other owners say their heat was almost "nuclear" and "vent melting", so I'm wondering where to start diagnosing the problem with my heat. Could it be as simple as the "auxilliary pump" next to the dreaded automated valve thing? What's the most likely cause of this recent change it perceived heat production?

Thanks much for your input....

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  #2  
Old 03-31-2010, 07:15 PM
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Not a single reply...?

Not a single reply...?
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  #3  
Old 03-31-2010, 08:14 PM
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How's your engine temp? If its not between 80-90C you'll get less then optimal heat. This is usually a thermostat gone bad.
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  #4  
Old 03-31-2010, 08:32 PM
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Uh-oh...

Well... my gauge seems to have been reading around 125?... I thought that was normal because it was the temp it was running at since I got it and it seems to run and perform great?

If it was running at that even hotter temperature, wouldn't the heat inside be even better?
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  #5  
Old 03-31-2010, 09:30 PM
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... in fact....

In fact, I don't even think my temperature guage even starts to register until the 100 mark on the dial... am I missing something here!....??
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  #6  
Old 04-01-2010, 12:26 AM
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Your gauge is in F. Most of them are in C. So your temps are fine.
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  #7  
Old 04-01-2010, 01:04 AM
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The difference with F and C degree gauges?

Strange... why would some be in F and some in C then... some difference in the way they were imported?

Too bad nobody seemed to take interest in where I should start diagnosing my interior heat problem also... anybody out there!?
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  #8  
Old 04-01-2010, 02:33 AM
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The earliest ones -- mid 70s -- were done in F. They switched to metric gauges (degrees C and bar oil pressure) very very VERY early in the production run. My best guess is that this was to save them having to build two different clusters in an already huge number of configurations. The font they printed the labels in changed at the same time, whenever the change was. The early early early ones were in some sort of all caps, if I remember right, and then they switched to bolder, more modern looking lettering -- and quit labeling the gauges. The "TANK" and "OIL" labels disappeared completely on all clusters from the late 70s, early 80s clean through until today. You just get degrees C symbol, a picture of an oil dripper, and a picture of a gas pump.
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  #9  
Old 04-01-2010, 11:03 AM
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Your car has the servo unit on it.

My car does not have the servo.

I do not know if your car has an auxillary heat pump or not.

Also, at what cabin temp do you set your CCU?

Also, low coolant level can affect cabin heat.
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  #10  
Old 04-01-2010, 11:46 AM
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125 is about 50F lower than you should be at.
80C is 175F
so you need to register between 175 and 195
pull your thermostat housing, I bet you have no thermostat. get the proper one in there, and your heat will work much better.
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"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
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  #11  
Old 04-01-2010, 08:15 PM
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Correction.. Mine >IS< actually at 175-F

Sorry... I was trying to go by memory when I said 125-F last time... it actually hovers nicely all the time at right about 175.

I might check the thermostat unit though and the coolant level just to be assured in those respects.

I've heard of a method for bypassing one's servo unit with tubing and a pull-valve deal... but I would kind of like to avoid that.

Provided a >do< have an auxilliary pump unit, and the servo.. how can I go about testing/checking those two things.

BTW... I put my thermostat all the way up at 85 and I'm still getting kind of just unheated air out of my vents.

Thanks again all...
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  #12  
Old 04-01-2010, 10:23 PM
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evil servo... evil servo...
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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 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
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  #13  
Old 04-01-2010, 10:38 PM
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It's probably a bad auxilliary pump since you have some heat, and not a bad servo. Make sure you put in a small fuse when you replace it. A stuck pump can take out the climate control amplifier.
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  #14  
Old 04-02-2010, 02:02 PM
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It does sound more like your pump. Unplug it and apply 12v to it... you should feel some slight vibration if it is running. If the pump runs OK, make sure it is getting power. Select the defrost position and check for power at the connector leading to the pump. Brown should be power, black ground.

As kerry suggested, at the very least put a fuse on that power wire. An inline fuse holder works well, I think a 1 amp fuse should do it. I ended up using a relay. If you do a search there are a few threads that cover that.

If your evil servo does go, I would suggest using the Unwired Tools replacement. It is a little pricey, but not really much more that a replacement servo that often fails again soon after anyway.

http://unwiredtools.com/accii.asp
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  #15  
Old 04-02-2010, 02:11 PM
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Before you pull anything . . .

Have you checked the coolant level in the Radiator?

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