Do you think I'm low on R-12? - PeachParts Mercedes-Benz Forum

Scott98 · #1 07-02-2011, 03:40 PM

Three or four years ago I installed a new AC compressor, receiver/drier, expansion valve and auxillary fan. I flushed the system, pulled a vacuum and filled it with R-12. My AC has worked perfectly until this summer. Just not blowing as cold as it used to.

I hooked up my manifold gauges which read 39-41psi low side and 215-220 high side. Outside temp is 86 degrees with 60 percent humidity. My hunch is simply that some R-12 has leaked out and it's time to add another can. However, I have no way of evacuating the system and weighing what's in there. I don't have a leak detection device and really don't want to invest in one.

What do you guys think?

Thanks,

Scott

leathermang · #2 07-02-2011, 03:51 PM

That you did everything right except for checking for leaks by using pressure with nitrogen and R22 and your refrigerant has leaked out... just as you suspect...
and that you are trying to do your own AC work with less investment in tools than it can be done DIY correctly.
Going by ' hunches' can cost a lot of money....and at some levels can ruin things which are perfectly fine right now...

Scott98 · #3 07-02-2011, 04:00 PM

Quote:

Originally Posted by leathermang

That you did everything right except for checking for leaks by using pressure with nitrogen and R22 and your refrigerant has leaked out... just as you suspect...
and that you are trying to do your own AC work with less investment in tools than it can be done DIY correctly.
Going by ' hunches' can cost a lot of money....and at some levels can ruin things which are perfectly fine right now...

I know you're right. Gotta invest in the tools if I want to do it right the first time. I was just a litte surprised that the low side pressure was still where it should have been. Had it been down around 20 I would have felt comfortable adding another can. I spent very, very little on this car. Just hate to invest all that money on tools I will likely not use again.

Scott

leathermang · #4 07-02-2011, 04:24 PM

I have found over my life that if I do invest in the special tool to do it right.... as compared to paying someone who may or may not do it right.. .that I almost always use the tool again at some time...
Perhaps you could farm out ... under your close supervision... just the pressure leak test... then go forth and finish the job... that would usually involve two times ..one to find the leak...one to make sure it was fixed ... and does not cover the fact that you do not have a way to capture what you have in the system AND clean it...

leathermang · #5 07-02-2011, 04:28 PM

Quote:

Originally Posted by Scott98

I know you're right..... I spent very, very little on this car. Scott

SOME PEOPLE would look at that last statement and say ' well, that means what you have saved so far should be available for the tools you really need to do this right '.....
There is Cheap..which I am ALL FOR... and then there is ' below minimum ability to be effective '.... which almost always costs more in the long run... sometimes a LOT MORE..

tyl604 · #6 07-02-2011, 08:16 PM

Don't you have a sight glass?

rscurtis · #7 07-02-2011, 08:30 PM

That was going to be my question. First, make sure there is no hot water flow through the system. It should not be necessary to E&R the system based on your pressures. Charge it until the bubbles in the SG are almost gone, then add another 6 ounces, and you should be good to go. I did this several weeks ago on my '83 300 and used a recovery machine(for its scale) and added 7 ounces of R12 that I had previously recovered. First attention in 4 years, I can't complain about that. I got to 38* on the center vents in 90* temps with a dew point of 72.

JHZR2 · #8 07-02-2011, 08:43 PM

+1 on the sight glass. If youre getting some cooling but not full cooling (and the compressor is cycling), then bubbles in the sightglass would be indicative.

engatwork · #9 07-02-2011, 09:00 PM

It does sound like you are low on refrigerant.

leathermang · #10 07-02-2011, 09:04 PM

I can not believe as many times in the last month I have posted that the FSM warns not to use the sight glass for filling purposes that yall have just posted that...
Most cars do not even have them anymore due to the potential ' add ' signal looking at the sight glass....
An AC system will work just fine at several oz less than its capacity....compared to ONE OZ over...
The only safe ways to put in refrigerant are weighing.. not possible in this case.. then the combo of pressures and vent temperature...
and even then the set up needs to be correct... which are listed many times in the AC thread at the top of the page...

tyl604 · #11 07-02-2011, 09:45 PM

Leathermang - I follow your posts and agree with you. However is it not correct that you can postulate low Freon if there are bubbles in the sight glass? At least that's what I remember from the good old days. My 81 300SD looks like a river current of bubbles going through the sight glass - and all the shops around here want to put Freeze 12 in it (not going to happen).

engatwork · #12 07-02-2011, 09:55 PM

tyl if you are ever on the way down I-16 and need some r12 I have some available for a good price

. Also have an automatic evacuate, vacuum and charge machine capable of handling r12 and 134 so we could determine exactly how much you would need to add. I'm within a mile of exit 71.

jusme · #13 07-02-2011, 10:02 PM

Check what the low side is reading at around 1100 rpm. In cars where they can over time develop fuel injector issues that influence idle speed, the drop in idle RPM that can happen over a few years will sometimes give you a false reading on the low side. Just raise the engine speed a bit while watching the gauge. No need to rev it up alot, just gently raise it a bit, and see if the pressure drops into the mid 20's. I had a 240D and 2 300D's that did this very thing. After the AC is fixed, maybe run a bit of diesel purge (in the isolated manner) through the injectors to help clean them up. But make sure to check your Idle RPM to ensure it's correct before adding refrigerant.

whunter · #14 07-02-2011, 10:17 PM

Quote:

Originally Posted by Scott98

Three or four years ago I installed a new AC compressor, receiver/drier, expansion valve and auxillary fan. I flushed the system, pulled a vacuum and filled it with R-12. My AC has worked perfectly until this summer. Just not blowing as cold as it used to.

I hooked up my manifold gauges which read 39-41psi low side and 215-220 high side. Outside temp is 86 degrees with 60 percent humidity. My hunch is simply that some R-12 has leaked out and it's time to add another can. However, I have no way of evacuating the system and weighing what's in there. I don't have a leak detection device and really don't want to invest in one.

What do you guys think?

Thanks,

Scott

You never mention which vehicle this is on?

If it has a mono valve, you must first check that the diaphragm has not failed = delivering heat.
It is a (cheap) common failure that gets overlooked.

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