I added r134a refrigerant on my 1985 300d. ac was converted couple of years ago to 134a. Anyway the climate control is set on the lowest temperature and when I added the refrigerant the ac lines became cold and the ac system accepted the entire can of r134a. The problem is even though the climate control was set up to the coldest temperature, my ac is blowing hot air as if it was set to heater. Do I need a new climate control? Is there a servo that turns so the air will pass the the ac core? The ac clutch work and the compressor pumped all the r134a to the system and the ac lines are cold. Please help. Thanks.

What are your pressures on the low side and high side?

It can be over charged, bad expansion valve, drier getting plugged up, plugged fins on the evaporator core.

Low pressure lines should be cold, while high pressure should be hot.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

it was a valve in the system that caused the same symptoms as my 500SL, it was stuck on hot and had to be replaced. I also had this happen once in my 300d, but fixed it in 5 seconds.

My car lingo is terrible, but there is some kind of plug in near the firewall towards the passenger side. Whenever my SL or my 300d decided to blow full hot air, I would simply unplug and replug this cord, and everything went back to normal. I can't remember what its called, some Auxillary switch???

I will try to take a picture of what I'm talking about if this doesn't make any sense. My ignorance of electrical/climate control systems is clearly showing.

Take it easy on me guys, I have no mechanical training whatsoever. So everthing I pick up usually doesn't have words associated to it.

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1985 500SL Euro w/ AMG bits 130k
1984 300SD Turbodiesel 192k
1980 240D Stick China 188k
2001 CLK55 AMG 101k
2007 S600 Biturbo 149k Overheated Project, IT'S ALIVE!!!

Do I need a new climate control? .... Not sure yet more info will be needed

Is there a servo that turns so the air will pass the the ac core? ... Yes, there is a diverter/flapper in the dash.

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92 300D 2.5L OM602 OBK #59

Mono valve could have a torn diaphragm. The monovalve does need 12 volts to close, and is fully open at 0 volts, so unplugging it will not help.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

I think the plug we mention is probably the heater control valve. Unplugging it gives full hot water to the climate system. There is a valve inside that could have a split rubber diaphram.

You might also have an issue with a vacuum pod not opening.

Thanks a lot for all the replies.

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TimD

That usually causes the heater to not work. You might try plugging or clamping one of you heater hoses and see if that improves things.

In Houston, it's highly unlikely that you are going to get acceptable a/c performance from R-134a, except maybe in the "winter" months.

Here is what I'm talking about. I saw my indy do it once when my AC was stuck on full heat, and it did the trick. Just unplugged, replugged.

I happened 2 other times on the SL (in 3 years)

and once in the 300d


My 300d


The SL

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1985 500SL Euro w/ AMG bits 130k
1984 300SD Turbodiesel 192k
1980 240D Stick China 188k
2001 CLK55 AMG 101k
2007 S600 Biturbo 149k Overheated Project, IT'S ALIVE!!!

that picture of the SL just brought to my attention the nastiness forming in the top left of the picture.

Another addition to the summer project list: clean, rustproof, touchup that area.

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1985 500SL Euro w/ AMG bits 130k
1984 300SD Turbodiesel 192k
1980 240D Stick China 188k
2001 CLK55 AMG 101k
2007 S600 Biturbo 149k Overheated Project, IT'S ALIVE!!!

Look at the picture of the monovalve and pinch it off, with a pair of visegrips or something and report back.

heater monovalve...hmm that makes sense.



I recently got a new compressor and was sure to pay the extra bucks for the R12. The 134 in my SL won't do the job unless I'm moving and the top is down.

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1985 500SL Euro w/ AMG bits 130k
1984 300SD Turbodiesel 192k
1980 240D Stick China 188k
2001 CLK55 AMG 101k
2007 S600 Biturbo 149k Overheated Project, IT'S ALIVE!!!

This is one of the biggest problems with R134. Your compressor will have hard time handling the high head pressures at temps of 95*F and higher too! I switched over to Envirosafe and it looks like this can be used in your state as well. I can hang meat in my car at 108*F!