jcgraff

I have a 1998 ML320 with manual controls for cabin temperature, that is I don't select a temperature. My problem is my A/C works intermittently, and my mechanic tells me he doesn't know what else to do since it is cooling properly when he has assessed it. I've reviewed multiple posts on A/C issues on MBWorld, but did not find others reporting intermittent issues like mine.

The technician says he has "hooked it up to the computer" and it checks fine, has checked freon level, etc.

The problem has only been noticed since the arrival of Spring. This ML 320 had its compressor replaced about two years ago. I was told at the time that there was an issue with the fuse box that commonly occurs as a result of the compressor failure, but they were able to repair the fuse box rather than replace it. Two years ago, I was told if future issues with the A/C cropped up that they might have to replace it. I may need to remind them of that. I wonder if that is my next step, but hate to start shot-gunning replacement parts without a best guess at the cause.

On some trips it works immediately on starting the vehicle and continues to work for the duration, which is typically 10 miles to work or back. On other trips, it does not cool at all, and I don't feel the compressor cycling when I am at stop lights. On some trips it doesn't come on initially, but does start cooling abruptly after driving a few miles. I can tell immediately when it starts running by temperature and humidity of the conditioned air, and feeling the compressor cycling.

Could this be due to borderline freon level causing the system to only intermittently allow the compressor to run? But, they've told me the freon pressure was tested and is fine. Is it an intermittent electrical connection that is causing the compressor not to cycle?

When the compressor was replaced two years ago, they put fluorescent dye in the AC system to help find leaks future leaks. Last fall I was beginning to notice the AC not cooling as well as it had earlier in the year, but it would cool every time it was turned on. I took the truck into the shop last January to get the A/C working for the coming heat, and they found that the A/C condenser was leaking. They also found the radiator was leaking. The A/C condenser, receiver/dryer, an A/C pressure line, and radiator were replaced per the parts list. I don't know if the AC worked after these repairs as it was a cold time in winter, and I didn't have a need to run it for a while. Then with the increasing number of warm days, I noticed the A/C was only working intermittently.

I planned to take it in for the intermittent AC, but before I could, a new issue arose with the air duct motor that controls the outside air/heat mixing door. I had that replaced, and that control is working well now. While there for the mixing door issue, I asked them to check the AC. They said they could not replicate an intermittent lack of A/C, but on the trip home my wife said it would not come on. It worked the next 4 drive, then did not come on, and works intermittently as described above since then.

There are no other shops for import repair within 90 miles, and I believe the technician is competent. What should I ask the technician to do/check next to troubleshoot the intermittent issue?

Thanks for your assistance,

Justin

C.P.

Hello,

Did you ever resolve your A/C problem? My 2000 ML320 is displaying the same problems.

Thanks