jcloudm

I have a 2009 C300 4Matic. I am experiencing a problem where in high heat (95-100 degrees F), after my car has been sitting in direct sun, the air conditioning does not work reliably. On many days, it goes from blowing cool air to very hot air, oscillating back and forth.

Last week I actually captured video of this with a digital thermometer, and over the course of 5 minutes it went from 75 to 85, then back down to 72 and then all the way up to 95 degrees, then back to 78 and all the way up to 95 directly out of the vents.

The dealer is struggling to reproduce the problem, as we don't have that many hot days here in Colorado. Has anyone experienced this, or have any ideas what could be causing it? Thanks in advance.

sudhanshu3

are you running the A/C in auto mode? if yes try without auto mode.

MBRedux

These are classic symptoms... you need to have the system checked for low refrigerant. The system will cool for about an hour tops, then the Evap coils will start to freeze up and the system will blow hot air instead. You have a small leak. You need to inject UV dye and a black-light to find it. Replace the faulty part and recharge. End of story. There is a compressor solenoid that shuts down when it detects a low 134a level.

jcloudm

Thanks, but they have repaired a leak that was causing effectively zero AC. The problem doesn't happen after an hour - it's immediate. (Within five minutes of turning on).

MBRedux

Then you need to throw on a set of gauges to see the pressure on both the low and high side. If that's ok, then check to see that the compressor is actually engaging when you turn on the AC. You can tell by the inner pulley rotating as the clutch engages. Have someone turn the system on and off as you observe. If it's not, and you have ok system pressure, then its a bad solenoid on the compressor. If not, they didn't fix the leak properly. Good luck.

jcloudm

That's a great idea. Non-car guy question: where in the engine compartment is the compressor?

cal1

Your getting some great advice here. I just wanted to add that pin hole leaks can be a ***** to chase down. A leak may have been identified and repaired, but there could be more. Slapping a set of gages back on the system will tell the story.

RLE

There is no clutch since the compressor is a swashplate design and changes flow slowly. MB went to this type more than ten years ago. My MBs before my W203 did have compressor clutches but no more.

MBRedux

The compressor is located usually along the front bottom of the engine, sometime on the left or right at 5 and 7 o'clock. It will have black belt running it and look something like this.



This is a swashplate compressor. Simply, do you see the pulley on the compressor? Now see the center plate with the three small rings on it? When the compressor is not engaged, that center plate is stationary but the outer pulley is rotating with the engine. When you turn on the AC, that center plate will now turn in unison with the pulley. Have someone turn the system on and off while you observe to see if this is happens. If not, either the solenoid is broken, or the system lost all it refrigerant once again. It sounds like this may be above your comprehension. Unfortunately, you will need to have it looked at by a professional shop.

RLE

Your description of somebody's compressor has nothing to do with our W204s since you are describing a clutch. It looks like you haven't looked at your own compressor which is undoubtedly just like mine as seen at the lower right in the photo. We have no small rings and the pulley of the compressor is fixed to the shaft by the large nut shown in the picture which turns whenever the engine is turning regardless of AC on or off.

BTW, notice the glossy paint recently polished and sealed (by random orbital, Menzerna Nano-polish and Sealer) as I continue preparing the car for the MB Car Show on 8/12.