A/C pressure diagnosis - PeachParts Mercedes-Benz Forum

lutzTD · #1 07-19-2009, 08:18 AM

I flushed my system replaced the compressor, expansion valve and dryer and charged with freeze-12 2 weeks ago. all was good until yesterday coming home from work. on the way to work no problem, on the way home the lines arent even getting cold. I hooked my guages up this morning. it is 75degrees out with a cold engine. upon initial hookup I got 70psi both sides, at idle it was 70 low 120 high, at 1500-2000 rpm its 80low 120 high. doies this mean mu expansion valve is clogged or bad? I got a $20 one from advance auto because I forgot to order it when I got my parts from peachparts. any ideas?

LNGfish · #2 07-19-2009, 08:57 AM

Is clutch engaged on the compressor? When I checked mine last at idle I had 40# suction and 175# discharge with compressor engaged turning. Where did U got your 12 at? Mine has 134a and works OK. Did you check compressor fuse? It's #12 on mine.

nhdoc · #3 07-19-2009, 09:07 AM

Quote:

Originally Posted by lutzTD

I flushed my system replaced the compressor, expansion valve and dryer and charged with freeze-12 2 weeks ago. all was good until yesterday coming home from work. on the way to work no problem, on the way home the lines arent even getting cold. I hooked my guages up this morning. it is 75degrees out with a cold engine. upon initial hookup I got 70psi both sides, at idle it was 70 low 120 high, at 1500-2000 rpm its 80low 120 high. doies this mean mu expansion valve is clogged or bad? I got a $20 one from advance auto because I forgot to order it when I got my parts from peachparts. any ideas?

Clogged expansion valves would usually have very low-low side pressures (even to the point of drawing a vacuum) and maybe high-high side pressures. Yours seem to indicate an expansion valve that is open too wide or maybe you have a leak and lost some refrigerant and are low on charge. I am not sure what the correct "static" reading should be with freeze 12. If you can get access to the expansion valve, try tapping it with a screwdriver handle and see if the readings change. Maybe it is just stuck wide open.

lutzTD · #4 07-19-2009, 12:09 PM

Quote:

Originally Posted by nhdoc

Clogged expansion valves would usually have very low-low side pressures (even to the point of drawing a vacuum) and maybe high-high side pressures. Yours seem to indicate an expansion valve that is open too wide or maybe you have a leak and lost some refrigerant and are low on charge. I am not sure what the correct "static" reading should be with freeze 12. If you can get access to the expansion valve, try tapping it with a screwdriver handle and see if the readings change. Maybe it is just stuck wide open.

yes I will try that.

I had readings of 35 and 180 when it was cooling very well. I put shrader valves in and I think the low side shrader is laeking so it is possible the system leaked down, I did noy know the evened out pressure was a symptom of a leak I am still learning

clutch is definitely engaged although since it is not cooling I was afraid and disconnected the pressure valve to disable the compressor clutch for now.

got the freeze-12 on ebay. it was around $70 for 6 cans