A/C High low reading Low high reading - PeachParts Mercedes-Benz Forum

ashedd · #1 06-18-2010, 05:55 PM

On my 300TD I have replaced the comp, drier, expansion valve and removed/cleaned the condenser/evap followed my flushing out the lines.

I charged with R-12 and I get a LOW reading of 55-60 psi and a HIGH reading of 50 psi. Coolish air out of vents. Comp run continuously and I have the aux fan blowing. It's about 85 outside right now. Only an occasional bubble in the sight glass. I vacuumed the system for 1.5 hours yesterday. Oil was added and one leak was found and fixed.

My A/C book isn't much help.

Any thoughts?

The comp is/was making a little noise and it's new not remain. The new comp had a brass "plug" on the back that looked to have a hole in the center of it but it was covered with tape/sticker. The comp instructions didn't mention the plug so I didn't remove the tape. Dunno if it needs removed or not.

Cr from Texas · #2 06-18-2010, 06:16 PM

I don't know the answer, but I do remember reading what problems could produce this type of readings. Do a search - I think you'll find the answer.

ashedd · #3 06-18-2010, 06:38 PM

I just confirmed the comp is making noises it shouldn't. I am recovering the r-12 now..... I am a little uneasy about watching my new 4 cans of r-12 get sucked into a recovery machine and not being able to see it or hold it in my hand(can).

ashedd · #4 06-18-2010, 09:22 PM

well I switched back to the old compressor and purged/charged. Got about 35psi LOW and just under 50psi HIGH... still kinds cool air out of the vents.

High side blockage? Blow out lines again? I can't get my old white industries recovery machine to recycle.... perhaps not enough freon in there. I hope my 4 cans of r12 are not full of water and air from the machine..

ashedd · #5 06-18-2010, 09:26 PM

I have some r134a.... think I should trouble shoot with it? I used the same synthetic oil ad dieselgiant so compatibility shouldn't be a problem... have no way to recover r134 though.

ashedd · #6 06-18-2010, 09:35 PM

POOP!

I went and checked my gauge set, it's raining outside now so I brought it inside.

I had the red hose backwards.... no shraider nipple on the end.... had it attached to the gauge side. It's funny cause I did the same thing yesterday with the yellow hose but caught it. And I already recovered the freon for a second time.

Will go out tomorrow and check again.

ashedd · #7 06-19-2010, 02:29 PM

I now get 36 psi LOW and 225 psi HIGH. Static pressure is 100 psi for both low and high. Few bubbles in sight glass NO leaks and coolish air from vent.

My a/c book has a scenario that matches this although the high is 200 not 225.... it says moisture in system. Before charging I had the vacuum pump on for 2 hours while I put the dash back in.

I believe my r-12 has moisture in it because of my recovery machine. It's an upright white industries recovery/recycle machine and I barely know how to use it. I have not been able to get it to recycle. It says to hold down a button and wait for the sight glass on the machine to change colors... I never see anything in the sight glass.

At this point I think I may leave the r-12 in the machine and fill back up with r-134a that I have in the garage, after a vacuum of course. This is the only way I know the freon is not contaminated with moisture.

Any ideas?

funola · #8 06-19-2010, 04:07 PM

Quote:

......The comp is/was making a little noise and it's new not remain. The new comp had a brass "plug" on the back that looked to have a hole in the center of it but it was covered with tape/sticker. The comp instructions didn't mention the plug so I didn't remove the tape. Dunno if it needs removed or not.

Any tape on the port(s) in a new compressor is to keep dirt out and must be removed before use.

ashedd · #9 06-19-2010, 04:14 PM

Well I charged with r134 and I am clear of moisture.... sight glass looks great. I get about 40 psi or so on the LOW and 225 on the HIGH. Vent temp seems cool.. I need to find my thermometer.

My aux fan does not run on it's own.. I suspect it has something to do with a circuit I disconnected from a fuse, don't remember which one. About a year ago I was having problems with this fuse blowing, it would take out the horn and servo, maybe turn signals? I figured out that something in that circuit was pulling too much current so I took it off the fuse... I did keep the servo hooked up since I needed warm air and not air from the surface of the sun.

Anyway that is a small issue I need to track down.

Does 40-45 psi sound too high for the LOW side with r134?

ashedd · #10 06-19-2010, 08:09 PM

I put 3 cans(12 oz each) of r134a in there.... I think it was too much. I have since got the LOW side down to 25 psi when revved up... about 35 at idle. 200 psi or so on the HIGH side. Seems good enough for now. Now I just need to return the new compressor for a new one.