Climate Control - Slow/Cold, Fast/Warm - PeachParts Mercedes-Benz Forum

jcd · #1 01-14-2002, 08:20 AM

I do have heat in my 1977 300D,,,,,however.

I have to be running at 60-70 to get heat. At slower speeds, air is cool.

I know that I have some vacuum actuators that need replacing, not sure about the servo (bought a used one from Mikemover, which I'll give a shot).

The aux water pump does work and the heater core is wide open and not obstructed. No monovalve on a '77 so that is not the issue.

BTW, I have the temp control dial pegged at 85 and get heat from the footwells and from the side vents (when open). No air from the center vents.

My experience with this car is the AC is never really cold and the heater is never really hot.

Thoughts from the experts

JCD

lrg · #2 01-14-2002, 01:35 PM

Don't know how comparable our systems are since my car is an '85 TD but my heat and A/C have always been marginal compared to most American cars you may have experience with. Everything seems to work but the REALLY hot or REALLY cold you can get on some cars just doesn't seem to be available. The A/C is best when on the highway and the compressor can really turn. I've had mine completely checked and recharged without much difference. Given a little time, the heat will get the car plenty warm but I never get a real hot blast on those days when you want that for a few minutes to warm your hands or feet. I'd be curious to hear from others but I think that's pretty normal.

As to the center vents, you probably need a new vacuum servo. The rubber bladder on mine split so the center vents wouldn't open and I never got air except at the defroster outlets. You can replace it by removing the glovebox and getting access through there. It's a fussy job and it helps to have small hands but it can be done (I did it) and beats removing the dash. Before you do all that though you might want to test to see if the servo is in fact bad by seeing if it will hold a vacuum, you might get really lucky and just have a loose connection.......Naaaaa.

Good Luck.

can-do · #3 01-14-2002, 01:59 PM

Greetings JCD,

If you are concerned about no heat from your center vents, don't be. The center vents are only used when you put the temp dial to the cold setting, whether it's outside air or a/c . These aren't used when in the heating mode. Seems strange, but that's the way it's designed. If you are getting fairly warm to warmer air out of your side vents in the heating mode, that's about normal. The temp wheel can be adjusted to increase the heat a little more, but it will also affect cooling in the Summer to some extent. I'd check the interior temp sensor in the right front speaker housing to see if it's all gunked up or if the lower hose that supplies blower air to it is deteriorated.

Charles

240 Ed · #4 01-16-2002, 10:39 PM

Can do

Hmmmm, I am getting heat from the center vents as well as every-whar else. I was thinking that these vents should be blowing cool air to the face, and warm air at the feet.
So, something isn't working...?

Breckman99 · #5 01-16-2002, 11:12 PM

Have you tried topping off the coolant? On my car if the coolant gets low there will be no heat unless you rev the engine up or are traveling pretty fast on the highway like in your case.

can-do · #6 01-18-2002, 12:08 AM

Greetings Ed,

Just wondering if the warm air you are getting out of your center vent is blowing out or just a trace of air movement? Reason I ask is that the rubber around the circle vent closures generally dry out over time allowing the vent to seep air out the center even when it's closed. Take a flashlight and shine into the center vents while you are in the heat mode and see if they are fully open, then switch to the defrost mode and see what they do. If the air you are getting out is not very warm, actually cool at engine operating temps, and you have the old style verticle climate control, I think we can help you adjust the temp wheel to get you back where you need to be.

Charles

Jaclson · #7 01-19-2002, 08:20 AM

JCD,

My 83 240 does the same thing though I do not have the automatic climate control. At idle, the air goes tepid. At 60 it's good and hot. Reminds me if my first car, a 66 bug. I have accepted it as an idiosyncrasy that adds a bizarre charm to the beast. (Sour grapes, huh?)

Jackson

240 Ed · #8 01-22-2002, 05:32 AM

Can Do

I have an 81 300CD with the horizontal controls, which are apparently new! I need to remove the glove box and check the foam seal around the sensor tube, and check the vaccuum flaps.
Have been busy with little things, fussing with the drivers seat, and freeing up the fast idle cable. I don't think it was used much, because it freed up with some penetrating oil and a twist of a plier.
That's what is fun to me, getting this stuff working again, enjoying the character of the car.
Just put on two Dunlop A2 on the front, and it steers much better than the Hankooks. Tightened the steering box and found the idler arm on the other side to be worn. will get a kit, and then the steering should be as new!

jcd · #9 01-22-2002, 07:52 AM

The cool thing about these cars is, they really respond to maintenance, which is relatively easy to do. My new motor mounts, motor shocks and 4 corners of Bilstein HD"s has made my 300D a different car.

On the heat front. It appears that everything is generally operating the way it should,,,,,with the possible exception of the auxillary heater pump. While it works when I test it from the battery, Per Larry Bibles diagnostic instructions, I'm not sure that it turns on via the climate control. I think that I get cool air at low speeds and idle is because water circulation drops with RPM['s and the aux pump is not turning on.

Question, what is the mechanism that runs the aux pump. Like I say, I know the motor works and the lines are clear....I'm just not so sure that the thing is turning on.

JCD

PS, 240,,,,,that's a pile of cars you have/have had

240 Ed · #10 01-23-2002, 12:12 AM

That sounds very logical! If the aux pump doesn't work, the heater won't get a fresh supply of hot water...? Wait,,,if the engine is turning over fast at speed, wouldn't that pump the water much faster? Perhaps the aux pump is for idle?

My pile of cars/motos are my current pile. All run well, but is a pain keeping batteries up. I only keep 2 cars insured tho.

jcd · #11 01-23-2002, 02:38 PM

That's why if one of the resident experts knows the mechanism for how and when the aux pump starts, that would be greatly appreciated.

JCD

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