Hot a/c in California

[wenchw/wrench]

Thanks for the wonderful forum!
I have a 1985 300 Turbo Diesel with 100,000 miles on the o/d. But my silver blue sedan has trouble in hot weather. The compressor clicks on, the system is charged (1st owner changed to R1-2-3, or whatever), but all I get is very hot air. I changed the in-dash temp sensor because it was cheap, then tried the ccu, and, as you all know, that was not cheap! But I still have hot air. I'm wondering what to try next. I've read many posts, but I'm not sure which part of the car to take apart next. I don't know if this is related, but the vacuum on the doorlocks is occasionally very slow. An overall vacuum problem?

I'm a semi-novice mechanic, having replaced the radio, fixed door locks, window switches, power antennae, water pump, odometer, brakes, etc. But I love success with my car projects, so now I'm hot and depressed. I'm looking forward to your ideas.

[joeym]

Hi Iwould check the pressures with a gauge if the compressor is workinf right feel for were the boil down is more then likley you will find a block at the drier or the expansion valve.joeym

[Palangi]

Time for a monovalve repair kit.

Paul is probably correct on this. Go to the firewall near the battery and you will see a valve with heater hoses connected and four screws on top. With engine cold and off, remove the four screws on top and lift up the cover. If it is flooded with coolant above the rubber diaphragm then get a monovalve repair kit. They used to cost about $35. Replace it and see that the cooling system is still full.

Good luck,

[joeym]

Hi If it was the mono valve he would at least get cold air for 5-10 minutes,it maybe a contribiuting factor,yet Iwould still make sure the a/c is ok.joeym

[wenchw/wrench]

My thanks for the suggestions, which I will follow up on. A really dumb question: in my friend's Ford the a/c compressor is cold, and water leaks from the bottom of the car as a/c should. My car is definitely NOT doing that. Originally I paid a real mechanic to charge the system. This is what he said was wrong. He sent me on my way with the soon-to-be hot a/c. No offence intended to him, but maybe it's not really charged, if there is no moisture and "cool running?"
I'm learning so much from you folk. Much appreciation.

[Johnhef]

I would go the monovalve route first since it is cheaper (about $70 now) but if that doesn't work, hook up the gauges and get a reading of your a/c pressures and go from there.

Don't buy a monovalve repair kit until you have checked it as I described earlier. There's no reason to buy parts without diagnosing first.

Good luck,

[wenchw/wrench]

Thank you, Mercedes mechanics! This weekend I will check out the monovalve, etc. (It's still too hot after I drive home from work to touch the engine.) Got a minute to answer my more recent dumb question about the lack of cold compressor and condensation? Might this be another monovalve symptom, or a symptom of a novice's lack of a/c knowledge?

[goertz]

where can you get a monovalve repair kit?

Click on Fastlane above if you don't want to take a trip to your neighborhood MB dealer.

Have a great day,

[jcyuhn]

It's real easy to tell if the compressor is running on your car. It's that thing on the drivers side of the engine; the bottom one. Has its own fan belt on your car.

Start the engine and see if its turning. Not just the pulley - that turns all the time - but the compressor itself. Look at the front face of the pulley - that's the compressor drive. It should be still with the a/c switched off, and turning with the a/c switched on.

That big metal pipe that runs across the front of the engine, just above the fan is the so-called low side of the a/c system. It should get cold and sweaty when the a/c is operating.

Larry is correct that you may have a mono-vavle problem; it's a common failure on this car. But if you don't have cold air for the first few minutes in the morning - before the engine warms up - then you have other problems too. Frankly, it sounds like you have a massive leak in the a/c system, and it has lost all its refrigerant. I expect you'll find it no longer switches on - the system detects when it is too low on refrigerant to safely run, and the compressor will not engage. My guess is that this is your problem.

- JimY

[wenchw/wrench]

Hello 300d a/c experts,
I am so excited! Following your considerable help: low and behold, when I unscrewed the monovalve cover, coolant came out the top. I pulled out the valve; it definitely looks "rough." The rubber gasket has a hole in it and some other metal rings are shredded. I ordered the kit. I'll put that in and see what happens next.
You guys are so great!