Should be an easy one.

What should the high/low pressure readings be on my '73 280 SEL? I am getting the system topped off tomorrow at a friends A/C shop and since he isn't a MB tech I would like to have the proper readings for him. Best part is the cost will only be R-12 at his cost. Sure helps to have a friend in the business.

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Mike Tangas
73 280 SEL 4.5

Hi Mike,

The pressure is a representation of the tempurature, high side for the condenser, low side for the evaporator.

Here is a temp/pressure table:
http://www.delanet.com/~pparish/pt-table.htm

You want the evaporator as cool as possible without ice (ice starts at 32 degree), therefore, it should be around 30 psi. The condensor should be as cool as possible too, 140 to 160 degrees, therefore, around 210 psi. When the R12 is charging, I use to put a big fan in front of the car to cool the condensor.

Have a nice hot day.

David

If the system has a sight glass, it should go bubbles and then clear then bubbles and then clear. This is a normal cycle for the Mercedes. When the aux fan is on, you will have more bubbles than not.

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Benzmac:
Donnie Drummonds
1991 GMC Syclone
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

Thanks for the info Benzmac. I'll keep an eye on the sight glass. Right now I have steady bubbles at all times.

Thanks for the pressure tables David. I imagine that most A/C systems are pretty much standard, but I have come to not rely on standards when dealing with the Benz, unless it's Benz standards.

With our little heat wave, I can tell you it's mighty toasty inland. Easily topping 100 degrees every day for the past five. A fully charged A/C will be a nice addition .

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Mike Tangas
73 280 SEL 4.5

Just got back from the A/C shop. All I can say is "brrrrr....."

The system took a little over 1 pound of R-12, pressures of 30/230 resulting with 42 degrees output at the center registers, ambient air temp at the time was 82.9 degrees in the shop. We tried 30/210 but the aux fan never kicked in, at 230 it did. Sight glass is cycling between bubbles/no bubbles just as Benzmac stated (more bubbles when fan kicked on).

Making for a very enjoyable ride in 100 degree heat. Now need to fix a couple air leaks in the ducts, losing cold air thru the bottom of dash with low output to drivers side vent, passenger side has good flow.

Overall, the interior of the car cooled off quickly and in short order I was able to turn the A/C down to low to maintain a comfortable level. Even in the mid-day sun, the horn ring was very cool to the touch after just a few minutes and the entire steering wheel was cool by the time I reached the house.

Benzmac & David, thanks for the help.



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Mike Tangas
73 280 SEL 4.5

Mike

Where is your friends shop in Temecula? I work in Temecula and would like to get my A/C checked out. You can e-mail me at cporter@guidant.com if you would like.

Thanks
Charlie Porter

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Charlie Porter
'80 300SD 375K+ miles