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Old 07-07-2002, 08:45 PM
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Join Date: Jan 2000
Location: PA
Posts: 5,440
300sdl Ac

I took the '87 300SDL out of my garage on a hot day last week and AC didn't work: air coming out of vents only slightly cool. It is probaby low on freon since it sit unused all winter.

What are good gage readings when I rechange it. I mean the high and low readings on the charging device gages. It still uses freon R12 as the coolant.

One other thing, I couldn't get any air to come out of the center air vent. Is this because the air was only slightly cool or is there something else wrong? Maybe I should get the air cold before I worry about the center air vent.

Thanks in advance for any help.

P E H

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Old 07-08-2002, 07:45 PM
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Join Date: Aug 2001
Location: Evansville, Indiana
Posts: 8,150
PEH:

My experiences with the 300SDL AC:


check the fuse -- if it is blown (or just corroded and breaks) you get only windshield air flow.

Check for vacuum -- you can use a Mitivac and pump down the green line in the engine compartment -- if the AC now works properly, you have a vac problem. If you can't pump it down, you have a leak somewhere. Low vac will send the air up the windshield instead of out the center vents. Very annoying.

For everything else working, but no cooling (200 psi high side or less, 50 psi low side), clamp off the hose to the monovalve (by the battery) -- if you then get cooling, replace the monovalve, it is sticking open or leaking. The heater core is in front of the evaporator, and if the monovalve is stuck open, the AC is working fine, just unable to lower the temp enough!

Proper readings are 250 psi high side or higher (depending on oustide temp -- cooling fan should start up at about 325 psi, cut off at 300). Low side should be about 34 psi, maybe slightly higher, again depending on outside temp. Really hot, and you won't get it down to regulated temp (expanstion valve all the way open). Low side reads degrees F as pressure (32 psi - 32 F) -- if it is lower, you have a restriction on the suction side or the air is very cold going into the evaporator and the expansion valve is closed.

Check pressures before recharging -- if the monovalve is stuck, you'd be putting excess freon in.

We've had all three of these on the 300D and/or 300SDL, both 87s.

You may also have crud in the evaporator, but I would be very surprised if that were the case since you are still using R-12. Crud in the system is usually only a problem if you blow a compressor or "black death" from ester oil and R134a.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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