Need Help: A/C on 2000 C280 -- pinpointing component
 

The symptoms: A/C is blowing, but not cooling. Compressor clutch engages. Low pressure line refrigerant pressure ~30psi (2.1bar) -- supposedly "normal" -- measured w/gauge.
After searching the threads on A/C, and reading the codes, the only thing wrong I could notice was code 7 (compr. press.) parameter, having range of 4.8 to 5.3 bar.

Any ideas of what the most likely scenario is? Any other diags I could run?

Any advise is much appreciated.

Is it stuck in the Economy mode?

Len

UPDATE: Added R134 anyway... and fixed the problem. Apparently, low side's pressure was not that significant: after adding freon, low side pressure stayed at ~ 30psi, while high side immediately jumped up (to over 10 bar), and cold air started blowing.

Thanks to all.

You might want to have the system checked for a leak(s).

Knowing the low side pressure alone, is not nearly enough information for diagnosing or even charging an a/c system.

I'm glad you're cool again,

This car has a variable displacement compressor. Instead of cycling on and off to control the evaporator temperature, it just changes displacement. So the low side is always going to read ~30PSI. You have a freon leak somewhere. Don't forget to add PAG oil, as you're losing that too.

- JimY

Yup. You should check the system for leaks. They are sealed and don't require topping up. If it's a slow leak, you should be fine for a while, but odds are you'll be filling it again. It might be better to find the real problem and fix it.

And again, the variable pressure system works a bit different, and you should pay attention to "high side" pressure values, but they will be all over the map depending on the evaporator's requirements. They are an indicator, but only indirectly, of charge level. Today, my compressor is running (as these systems always do) but my pressure vlaues at 3-4bar thanks to the outside temp being 5C and there is little pressure required to keep the evaporator at 4C or so.

Jim, John, et al. -- thanks again! it was exactly an explanation like the one above that I was looking for... and no MB shop, including dealerships, would spell it out --- only the usual "bring the car in.."

Alex.