Author Topic: A/C and Heater battling it out...  (Read 4702 times)

Stork

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A/C and Heater battling it out...
« on: 21 March 2011, 04:26 PM »
So I am driving my 280S on the highway and decide to put up the windows and turn on the A/C. The A/C is blowing nice and cold but it is now in a fight with the hot air coming out of the side vents and the dash.
Just so you all know... drivers side left hand drive, from left to right the levers are down, down, up, and down. Top fan control is on two and bottom is turned all the way to cold.
From the side vent I get a steady stream of hot air so I close those. From the top of the dash (defrost) I get very weak air flow but it is hot as well.
I'm I missing something here? Should my levers be in different positions?
Is the A/C only supposed to come out of the middle two vents?
Is there a way to stop the hot air from escaping the top of the dash (defrost?)
If I activate the defrost it works great blowing hot air at a rapid rate. So the defrost 'on' is working properly
Since summer is around the corner is there a way to shut off the heat completely?
Even thought I do have a very well functioning A/C the hot air escaping really does change the temp inside to the point that I turned off the A/C and drove with the windows open.
Any help? is this normal operation or is something going on?
Robert
1975 280S 76,000 miles, Brown
On the list to buy:
1972-75 280 SE
My ex mercedes Benz:
300 SD (first MB)
1972 280 SE 4.5 (owned 14 years)

koan

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Re: A/C and Heater battling it out...
« Reply #1 on: 21 March 2011, 08:28 PM »
I'm I missing something here? Should my levers be in different positions?

down down up down is correct

Quote
Is the A/C only supposed to come out of the middle two vents?

No, I think cold air should come out of the side vents too.

Quote
Is there a way to stop the hot air from escaping the top of the dash (defrost?)
If I activate the defrost it works great blowing hot air at a rapid rate. So the defrost 'on' is working properly

Sounds like one of two things, the vacuum controlled heater valve on the engine side of the firewall is stuck open possibly because it's not getting vacuum, or, your left and/or right heat levers are not adjusted correctly, when at the bottom position they should be supplying vacuum to the heater valve to close it, either lever moved off its stop cuts the vacuum to heater valve and it opens fully. Amount of heat is determined by air mixing flaps not water flow.
 
koan
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WGB

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Re: A/C and Heater battling it out...
« Reply #2 on: 22 March 2011, 01:08 AM »
Either your heater valve is malfunctioning or you have the standard internal foam/hinge issue and the flaps are jamming and stopping both hot air levers from bottoming correctly and pulling in teh vacuum that shuts off the heater valve..

This is the major problem with this system and the quick and dirty work around if one or both heat levers are not totally bottomed in their slots is to remove the knee rolls and loosen the 10mm nut seen on either side and this disengages the heat control from the flaps.

This will allow the heater to turn off completely but it depends where your flaps are left whether or not you have acceptable airflow.

The real fix is to remove the dashboard and the heater box and repair/replace..........

Bill 

jbrasile

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Re: A/C and Heater battling it out...
« Reply #3 on: 22 March 2011, 06:43 AM »
Robert,

I agree with what's been said, you probably have a bad heater valve.

I have not seen a stuck flap but it is possible that they need to be adjusted so you have better air flow control. When working properly the manual a/c system in these cars is simply awesome, providing very cold temps and excellent control.

First thing to do is check the heater valve with a vacuum pump, hook it up and evacuate, see if the valve closes and stays closed, and by the way closed is in the direction of the passenger side of the car.

Tks,

Joe

oscar

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Re: A/C and Heater battling it out...
« Reply #4 on: 22 March 2011, 09:51 AM »
Very much agree.  Resting position for the heater tap is open so a dodgy vacuum element or no vacuum to the element will send coolant to the heater core and the fact you're getting heat in the side vents there is due to a mix of flap adjustment and degraded foam seals like others have said.  Not really worth worrying about IMO because once the heater tap vacuum element is replaced there'll only be heat when you want it.  You'll still have a bit of air going places you don't want to, like the windshield, when you've set the levers for the floor and face, but it wont be a drama unless a flap is inoperative.  Anyhow, check your owners manual if you have one, for lever operation and what does what.  There's a complete description with photos about 20 pages in.

An easy way to test the tap vacuum element if you don't have a vac pump is to physically close the tap and occlude the vacuum connection to the vacuum element with your finger.  There's a spring inside the element that counteracts vacuum.  If the diaphragm inside is cactus the spring will push the actuating lever out of the element and push the plastic arm on the tap to open position.  Once you've done that and find the diaphragm isn't holding a vacuum you can take the pink/orange cap off to view the diaphragm too if you wish.

Tap on, white plastic lever below tap at 6 o'clock.


Tap off, white lever at 7-8 o'clock.  The tap should stay there if diaphragm has no leaks.  If you do need a new vacuum element and whilst you're waiting for it to arrive, as a short term remedy you can disconnect the actuating arm of the vacuum element to the plastic lever then push the lever to the 7-8 o'clock position.  It will stay closed whilst you drive around.  You'll just have no heating which I assume wont be a problem this time of year for you.


Also check your version of tap and element before you order.  There are ones like mine pictured where you can replace just the vacuum element.


Then there's others that have been converted with an aftermarket assembly that has a complete plastic tap and element combined.  Only get this if someone already removed the original alloy tap.





« Last Edit: 22 March 2011, 09:55 AM by oscar »
1973 350SE, my first & fave

Stork

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Re: A/C and Heater battling it out...
« Reply #5 on: 22 March 2011, 05:33 PM »
Thanks guys! And thank you for the pictures. It makes life a lot easier when one can see what one has to do! Note to everyone, post a picture... it is worth a thousand words! Thanks Oscar!
I am off to Costa Rica Thursday for my wife's cousins wedding so I will run Oscars test tomorrow. That way I can order the part and it will be here when I get back Monday. Hopefully this resolves the issues especially since I am pretty sure this summer is going to be a hot and humide one :-\!
Robert
1975 280S 76,000 miles, Brown
On the list to buy:
1972-75 280 SE
My ex mercedes Benz:
300 SD (first MB)
1972 280 SE 4.5 (owned 14 years)

tomw116

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Re: A/C and Heater battling it out...
« Reply #6 on: 27 March 2011, 02:02 PM »
On my 116 300SD from '79, I have several valves that probably used to be vacuum controlled, but the controls are removed, and I'm looking at valves that I can manually set to prevent coolant flow to the heater.

My question - there do not seem to be "H" fittings - i.e. if I shut the valves, there is not a 'bypass' to let the coolant circulate from the "to heater from engine" back to the "from heater to engine" connections.

Does there need to be such a thing - i.e. will I have coolant circulation issues in the engine if I simply shut the valves to the heater?

Thankyou,
-Tom

jbrasile

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Re: A/C and Heater battling it out...
« Reply #7 on: 27 March 2011, 06:55 PM »
Tom,

The Climate Controlsystem in US cars and some euro is so unforgiving once it starts giving trouble.

If I understand correctly you are trying to block coolant flow into the heater core in order to get max a/c is that right?

Well, first of all have you identified the source of your vacuum leaks?

The valves behind the console control the opening and closing of flaps based on your temp selection. If your system has already been tampered with and all you want to do is stop coolant from entering the heater core you need to block both the feeding and return lines, I had a 500SLC that had this done by a previous owner and if I remember correctly you block the lower  line from the servo to the y pipe and the return line which is on the driver's side.

Hope this helps...

Tks,

Joe

Stork

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Re: A/C and Heater battling it out...
« Reply #8 on: 30 March 2011, 06:23 PM »
Ran the test today, Vacuum is good but not great so it is not pulling hard enough on the heater tap (It is the second one in the pictures) So I have to eventually find the leak. For now I am going to activate (and tie) the tap to stop the coolant. I am going to order a new tap  and replace it. Once replaced I will test it hopefully the the tap works and I have cold air coming out of all vents. After that is working it is time to find the vacuum leak. So for now I will wait for the part, and tackle the rest in due time...
Robert
1975 280S 76,000 miles, Brown
On the list to buy:
1972-75 280 SE
My ex mercedes Benz:
300 SD (first MB)
1972 280 SE 4.5 (owned 14 years)

WGB

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Re: A/C and Heater battling it out...
« Reply #9 on: 30 March 2011, 06:35 PM »
I assume that both heat levers bottom completely as you will not get adequate vacuum unless they do.

Bill

jbrasile

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Re: A/C and Heater battling it out...
« Reply #10 on: 31 March 2011, 06:09 AM »
Robert,

If with both heat levers down you still don't have enough vacuum to close the valve, there might be a leak somehere. There is a procedure in the Technical Library to test for leaks from the heater levers so you can assure they are working properly, but I have never seen a bad one so the new tap will most likely solve the problem.

Tks,

Joe

Stork

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Re: A/C and Heater battling it out...
« Reply #11 on: 08 April 2011, 09:55 AM »
Replaced the tap but no change then so I took your advice and we noticed that one of the levers was not going all the way down. we opened up the glove compartment and found that someone had not connected the levers properly, probably the last owner that replace the ac system. So we hooked it up properly... but since we already had the headers out we have not tested it as of yet. I will find out Monday if its working properly...
Robert
1975 280S 76,000 miles, Brown
On the list to buy:
1972-75 280 SE
My ex mercedes Benz:
300 SD (first MB)
1972 280 SE 4.5 (owned 14 years)

jbrasile

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Re: A/C and Heater battling it out...
« Reply #12 on: 08 April 2011, 04:56 PM »
Robert, the levers are adjustable too. You just need to remove the panels under the dash on both sides to gain access to the bolts, what you want is for the levers to go all the way down while closing the heater distribution flaps completely. Once you look at it you will see what I mean. After loosening the bolts you can move the flaps tightly shut by hand  and while holding the controls down, re-tighten the bolts.

Tks,

Joe

WGB

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Re: A/C and Heater battling it out...
« Reply #13 on: 08 April 2011, 08:57 PM »
You may still have problems if your foam hinges are snafu.

Bill

koan

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Re: A/C and Heater battling it out...
« Reply #14 on: 08 April 2011, 11:37 PM »
You may still have problems if your foam hinges are snafu.

I was about to say the same thing.

Deteriorating foam hinges on the flaps can cause the flaps and levers to jam. A non-fix is to disconnect the jamming lever.

koan
Boogity, Boogity, Boogity, Amen!