AC not working - how to troubleshoot?

[rayhennig]

Moderator edit: Cleaved this posts off a thread discussing a slow leak from the service port (link).

My 300CE-24 aircon was brought back to life in 2017 by a highly respected independent in the UK. It's worked ever since, even during last year's roasting summer.

But this year it has decided to give up. And I'm a bit dense when it comes to how all this works.

Symptoms? No cooling. When I hit the EC button, I hear and see the revs drop slightly so something is being triggered. That's about the limit of my knowledge.

We have a garage about 8 Km away and they advertise aircon re-gas, etc. Should I just go to them for an assessment.

Any comments/advice would be much appreciated.

Best to all.

RayH

 

[gerryvz]

Hope I'm not hijacking this thread.

My 300CE-24 aircon was brought back to life in 2017 by a highly respected independent in the UK. It's worked ever since, even during last year's roasting summer.

But this year it has decided to give up. And I'm a bit dense when it comes to how all this works.

Symptoms? No cooling. When I hit the EC button, I hear and see the revs drop slightly so something is being triggered. That's about the limit of my knowledge.

We have a garage about 8 Km away and they advertise aircon re-gas, etc. Should I just go to them for an assessment.

Any comments/advice would be much appreciated.

Best to all.

RayH

You should check the pressure in the A/C system. That will immediately tell you if there is enough refrigerant in the system, at least to trigger the compressor on. It's easy to do this by just putting an A/C gauge on the high side and low side ports of the system, and they should be able to tell in 5 minutes if there is enough refrigerant in the system.

If the refrigerant has escaped to the point where pressure is too low to turn on the compressor, a "Re-gas" is a band-aid -- it will work in the short term to give you cool air, but it will leak out (sooner or later) depending on the severity of the leak, and where it is.

So, the proper thing to do would be to have them put refrigerant with dye in the system, or add dye after they re-gas it, which will (used with an ultraviolet light) tell you where the leak is occurring by presence of the dye. Most often this is at hose connections and/or the valves at the high side or low-side ports. Hoses themselves generally tend to be fine in the middle, but can leak at the ends where the fittings attach to the hoses (where they are clamped to the hose).

Occasionally compressors can leak, as well. Sometimes this is a mechanical issue, and sometimes it's just in need of replacement of a green o-ring at one of the fittings or atop the compressor at the manifold.

On many cars, MB no longer sells the A/C hoses. This is generally not a problem, as any competent hose shop or mechanic shop with good A/C experience can custom make a hose based on the original hose length/pattern/fittings/spec. Generally this is also pretty cheap.

A thorough and methodical diagnosis is the way to go with A/C. They all leak sooner or later.

If the system is not showing any leaks, then it's likely a control issue, either with the center console control, or an electrical connection at the compressor itself. But I'd start with checking system pressure and re-gassing, and looking for leaks.

Good luck !