Yes, this is another "my AC isn't cooling!" thread, but my searches yielded nothing I didn't already know. On to business.

My 87 SDL was converted to 134 late last summer, and the HVAC system was redone. It worked like a charm. Now, as summer descends ever-so-gently on Toronto, I found occasion to turn on the A/C for the first time since last September. The compressor clicks on, the refrigerant hisses and gurgles softly behind the dash--and ambient temperature air comes out the vents.

All things considered, if the compressor works in tandem with the pushbuttons, the control panel and Klima should be working. No hot air is coming from the vents, and I changed the monovalve before having the A/C redone last summer, so I can hopefully eliminate that.

Could I simply need a recharge?

Thanks, and happy cooling to all.

DL

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1995 E300 146,000 miles "Celia"--sold
1993 300sd 131,000 miles "Konstanze"--with Mom in Tampa
1987 300sdl 225,000 miles "Frau Grau"
1980 300sd 164,000 miles "Old Yeller"--sold

anyone?

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1995 E300 146,000 miles "Celia"--sold
1993 300sd 131,000 miles "Konstanze"--with Mom in Tampa
1987 300sdl 225,000 miles "Frau Grau"
1980 300sd 164,000 miles "Old Yeller"--sold

If the compressor is running, you should have some cooling. It's time to connect a gauge set to see what's going on. You could be very low on refrigerant (which is the most likely problem) or there could be a restriction.

The gauge set can be had for under $100 US, and is a good tool to own.

...the compressor being on? Shouldn't it not activate if refrigerant is low? If so, then I should probably look at the expansion valve. It's just surprising to me that the system would have problems like this less than a year after reconditioning. I just hope the problem isn't lurking somewhere under my dash, deep in the bowels of no-man's land...

Thanks,

DL

__________________
1995 E300 146,000 miles "Celia"--sold
1993 300sd 131,000 miles "Konstanze"--with Mom in Tampa
1987 300sdl 225,000 miles "Frau Grau"
1980 300sd 164,000 miles "Old Yeller"--sold

If it was not reconditioned properly... well, there will be issues. Wrong o-rings, incorrect oil, etc, etc.

You need to start at the top. Visually see if the compressor is turning when the climate unit is turned on. If not, you'll have to verify the climate unit works. Then the Klima relay. Then the speed sensor.

Also check pressures, this tells everything.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

You may hear the compressor engage when you operate the buttons on the dash.........but.........how long does it remain engaged? Sometimes they engage properly for about 45 seconds before the Klima takes them offline for some reason. It's not an instantaneous fault.

So, watch the compressor and see if it remains turning for at least five minutes. If so, and you still have poor cooling, you've got issues with the amount of freon in the system or a problem with the compressor or the expansion valve.

All the above is good advice but I would like to add my way of checking the basics. Turn on the A/C. Make sure the compressor is running. Feel the LOW (big) A/C hose at a metal section. It should be cold, like maybe 35 to 40 degrees. If it is cold than you have a problem inside the car like the devert valve or monovalve. If the hose is not cold then feel the line coming out of the condenser going to the expansion valve. If it is just warm, then you are probable low on freon, If it is very hot then you may have a restriction. Now is the time to hook up the gauges and see witch it is.. The initial test only takes a few seconds but will save you a lot of time in the long run.

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84 500 SEL (307,xxx miles)

Maybe we can start a mutual aid society......

Bought car in Feb 2006. Relatively low mileage (about 90K miles).

Problem symptom is that the climate control seems to heat the cabin too much and delivers roasting air to the cabin regardless of the temperature setting on the CCU dial. Also regardless of CCU push button setting.

Over the past year the problem has grown from being occasional and intermittent to an almost solid hard fault situation. This weekend I drove for a 200 mile round trip and actually got the climate system to operate properly in cooling mode for 30 minutes of the entire trip. When it works AC works fine....

Each CCU setting has seemed to fail progessively from right to left!!! AC alway worked fine with reasonable temp control on the left most setting (solid up and down arrow) until two weeks ago when it began to roast the bejesus out of us too.

I replaced the mono valve insert and the in cabin temp sensor last summer.

ONE MAJOR THING THAT CONCERNS ME IS THAT WITH THE CCU SWITCHED OFF AT SPEED, ROASTING HOT AIR IS DELIVERED TO THE CENTRE AND SIDE DASH VENTS. No fan action - just ram effect from vehicle motion.

I thought my CCU was fried and am about to replace it, along with the vacuum pod buried behind the CCU at the same time. However this "heat with CCU off" issue has me worried that I have a jammed monovalve as well. Does the valve not close and shut off hot water flow with the CCU off?

Can I test this by simply disconnecting the mono valve power leads?

The monovalve needs 12V to close. See if you can test for 12V when the problem occurs. If the CCU fails to close the circuit to the monovalve (I believe that the ground is controlled), then you'll get unlimited heat.

So, the problem could simply be a bad CCU.

However, I have a similar problem on the '87. I replaced the CCU and I'm not fully convinced the problem is completely eliminated. It can still provide too much heat at times.