Need A/C help - PeachParts Mercedes-Benz Forum

burford · #1 07-06-2010, 10:54 AM

First let me tell you what I have done. Over the years I have repaired, maintained the a/c systems in my cars and in my home. So, I do know a little about how they work. I have a 1984SD 300 in excellent condition. I love the car and would like to keep it. Here in south central Florida it gets very hot so I need a good working a/c. Now let me tell you what I have done.
Using the fine article on Diesel Giant web site. I did everything exactly as on the web site . I took every thing apart, flushed the condenser, evaporator, and all the lines. Blew everything out several times. Installed a new R4 compressor, dryer and expansion valve. Drained the new compressor poured in 4 oz of synthetic oil and 4 oz in the dryer. I wanted a R12 valve but could only get an R34a. Vacuumed it out for an hour and ½ filled it with some R12 I had. Checked the vent temperature at 60 degrees blower on high. Put blower on low, vent temp went to 59 degrees. Engine rpm @ 2000. Ambient temp is 95 with high humidity. Air will not come out of the center vents unless I move the vent lever to the center of its range. This may be important I don’t know.
My pressures are low side varies from 35 down to 20, high side 210 to 240 due to the expansion valve working. Inside at the evaporator the temp at the input right above the expansion valve is 60 and the out put back to the valve is also 60 degrees??? The high side input to the valve is barely warm. At the condenser the input is 127 deg. And output is 98 deg. What is going on here? Looks like the evaporator is starved. When I blew air through it there was plenty of volume. How could this be? I checked the coolant hoses from the monovalve and they are cool so I don’t think it is a heater problem as the vent temp at start up is 60 degrees with a cold engine. The does compressor does not cycle either.
Because I don’t know where to go from here I am going to change out the climate control with one I have I know is good.
I don’t want to be like gpracer on the forum who sold his Mercedes because he had the same problem as I do. All help will be greatly appreciated.

zeke · #2 07-06-2010, 11:33 AM

Don't know, byt one thing you didn't mention is whether you have checked the dash temp sensor tube.

I think you have to remove the glove box and find the foam tube that connects to the little vent on the dash. You can replace it with some pipe insulation.

Cr from Texas · #3 07-06-2010, 11:47 AM

Quote:

Originally Posted by burford

Vacuumed it out for an hour and ½ filled it with some R12 I had.

You only vacuumed for an hour? All of your results are for a 1/2 filled system?

leathermang · #4 07-06-2010, 12:19 PM

If you could not find a full load of R12 why did you not just install R134a ? Are you failing to tell us what the rest of your plans were with regards to getting the rest of the R12 you need ?
What are you expecting out of a half filled system ?

zeke · #5 07-06-2010, 12:52 PM

Quote:

Originally Posted by leathermang

If you could not find a full load of R12 why did you not just install R134a ? Are you failing to tell us what the rest of your plans were with regards to getting the rest of the R12 you need ?
What are you expecting out of a half filled system ?

Good catch I missed that!

47dodge · #6 07-06-2010, 07:10 PM

Although the grammer is a bit sloppy,(not that mine is a lot better) I took what he meant to be; vacuumed for an hour and a half, then filled with r12. He needs to clarify which is true.

leathermang · #7 07-06-2010, 07:19 PM

Well, that could be true. Hope he stops back by soon and clarifies...

I also feel that one and one half hours on the vacuum is not enough to ensure that any moisture present is boiled out...

If there had been an " and " after the 1/2 it would sound more like a full charge of R12..
as is seems like that went with the R12 end of the sentence...

Yak · #8 07-06-2010, 08:31 PM

Dudes - read the post. And check your own "grammer" at the door.

In order: byt = but; extra space between system and the question mark, grammer = grammar, etc. If you ain't gonna help, then don't post! And spelling and grammar corrections ain't helping!

At least CR from Texas asked constructive questions to clarify ambiguities in the admittedly poorly edited synopsis from the OP. He was trying to be helpful.

Pertinent questions for the OP:
How much R12 into the system, in pounds or kg please, not "2 cans."
Vacuumed for 1 hour, or 1.5 hours?
How long did you wait to see if it held vacuum after the pump was removed?
Synthetic oil? Not "synthetic PAG" hopefully. Ester, perhaps?
Any indications in the sight glass - bubbles, streaks, foam?

I'd recommend he read here, and see if that helps:

http://www.aircondition.com/tech/questions/82/

I don't know enough about A/C to offer specific advice based on the details, or I would.

vstech · #9 07-06-2010, 08:59 PM

98 out 127in with 95 ambient is just fine, but I'd need to know what the line pressure is to know how your charge is. The temp could be a result of the center vents not opening, and you reading a mix of interior and exterior air. are your windows open during this? are you in shade or sun?

burford · #10 07-06-2010, 09:49 PM

Sorry about the grammer but I had alot of info to type.
2.9 lbs of R12 or as close as I could get.
Vacuumed for 1.5 hrs.
Held good vacuum for 20 minutes.
I used BG's Frigi Quiet 2 synthetic oil.
Some bubbles in sight glass.
I was in my garage in the shade.
I let it set over night so I could check vent temp with a cold engine to see if outside air was a factor.
Thanks for everyone's input.

airedale2 · #11 07-06-2010, 09:53 PM

Just finished redoing my ac as well. New compressor works compressor, mineral oil, new expansion valve (r134), new dryer and es12a. 58degrees at idle. Your high side pressure seems a little high. My temps while on the road are down to 47 with a digital thermometer. I need to refill my fan clutch with oil which should bring me down to the high 30s. Really need to check your fan clutch.

vstech · #12 07-06-2010, 09:57 PM

my 83SD requires 3.3 lbs R12...

burford · #13 07-07-2010, 09:03 AM

Quote:

Originally Posted by zeke

Don't know, byt one thing you didn't mention is whether you have checked the dash temp sensor tube.

I think you have to remove the glove box and find the foam tube that connects to the little vent on the dash. You can replace it with some pipe insulation.

I looked for it before but did not see it. I will look again.

#14 07-07-2010, 10:45 AM

I'm not familiar with the 126 cars. Do they have a foam tube to the temp sensor as do the 123 ACC cars?

burford · #15 07-08-2010, 10:36 PM

I don't know yet but I will post soon. I had a big fan blowing on the condensor so I could simulate road conditions as best I could. I see others on the forum with 126's have the same problem. I will road test tomorrow.
The cabin air sensor on my 126 chassis is above the rear mirror. The way you can test the tube is to turn on the air and put a small piece of tissue over the sensor and the air flow will keep it there.
The fan clutch is good.