R12 A/C pressure....Low side issues - PeachParts Mercedes-Benz Forum

ps2cho · #1 02-07-2011, 04:37 PM

78F outside today
Something is definitely wrong...

A/C clutch engages (sometimes), but its just ambient air coming out of the vents.

6 months ago I replaced Evaporator, Receiver/Drier + expansion valve. All lines were flushed and everything was working amazing until recently.

Static

A/C On -- Clutch Engaged (vent temps are not cold. A/C not functioning

There seems to be no pressure at all on the low side

As soon as I turn the A/C off, high+low return to static pressures.
What do these pressures tell me? Just low refrigerant or something else?

fdanielson · #2 02-07-2011, 05:15 PM

It's probably low refrigerant. If your car has a sight glass on the receiver/drier you will see foam instead of liquid. If the refrigerant is that low the compressor will usually cycle on and off and you will see the pressure go up and down with the compressor cycling. Don't run it with refrigerant this low as it's a good way to damage your compressor.

This probably won't sound very friendly but if you are unsure of what is going on with your air conditioner you should find someone who is. I'm sorry if that sounds harsh. How did you get that gauge set connected to your R12 system?

engatwork · #3 02-07-2011, 05:25 PM

If you have access to the machine remove the freon and vacuum it down. Try to find the leak, repair as necessary and then recharge with the proper amount of refrigerant. Looks like you may have a leak.

leathermang · #4 02-07-2011, 05:33 PM

Good advice already given.. and not harsh at all... safety and frugality are important to most of us...

Remember after you have put it back together having cured whatever leak you might find..

the best way to check for complete cure is to use pressure... since some orings will seal with vacuum but leak in pressure mode... and pressure mode is where you want them working correctly..

The EPA allows you , AS A TEST medium WHICH you CAN VENT to the atmosphere, Nitrogen and four ounces of R22... which will show up with an electronic sniffer... very important since dye and soap bubbles are pretty much useless finding a leak in the evaporator ( do not ask me how I discovered this )...... and you might as well test the WHOLE system at one time..

There are some really good threads in the archives available by using the search function.. most AC experts are hibernating right now...

vstech · #5 02-07-2011, 08:20 PM

nahh. I'm not hibernating at all!

good advice so far. in addition to my sniffer, I like the ultrasonic testers. they are just plain wonderful at finding any size leak, anywhere!

those pressures indicate your system is very low on refrigerant, or it's really cold outside. since you stated 78F outside temp, I'm going with low charge. you've got a leak, if it's this low in 6 months, you should not have issue finding the leak with a sniffer! no point removing the charge yet. use it to find the leak with the sniffer!

ps2cho · #6 02-07-2011, 09:04 PM

Quote:

Originally Posted by fdanielson

It's probably low refrigerant. If your car has a sight glass on the receiver/drier you will see foam instead of liquid. If the refrigerant is that low the compressor will usually cycle on and off and you will see the pressure go up and down with the compressor cycling. Don't run it with refrigerant this low as it's a good way to damage your compressor.

This probably won't sound very friendly but if you are unsure of what is going on with your air conditioner you should find someone who is. I'm sorry if that sounds harsh. How did you get that gauge set connected to your R12 system?

The only thing I'll be handing over is my wallet... I'm looking to learn.

I have a feeling it could be leaking from the gasket at the compressor (that big rectangle one). When I refreshed the system and back-converted from r134a to r12, I forgot that particular gasket as I did not know where it went.

I was just concerned that the compressor could have failed and was not functioning anymore, but if you guys believe that it is simply a low charge, I feel much better and will look towards finding it.

How did I get the gauge set to work? The included hoses are R12 compatible...

leathermang · #7 02-07-2011, 09:51 PM

Being low on refrigerant can cause the compressor to fail because it is lubed by oil which is mixed with the refrigerant and circulated through the system... ( particularly if someone has the Delco R-4 .. which I assume you do NOT have ) ...
So " Simply " low ... is not what we are communicating...
and the chances are some oil was lost in the leak.... .
but the bad thing is that there is no test for determining how much oil you do have in the system... thus to be safe and sure as to amount ( and too much is also a problem ).... you have to evacuate the system and measure the amount you add...

vstech · #8 02-08-2011, 12:40 PM

close... simply evacuating the system will NOT remove but the slightest amounts of oil from a system. the only way to get oil out of a system is by flushing each component. both coils, all 4 hoses, replacing the dryer, and installing a NEW compressor... no way to know how much oil is in the compressor, and it's a really bad idea to flush a compressor...

compu_85 · #9 02-08-2011, 01:05 PM

Can you just leave the compressor on end for an extended period?

engatwork · #10 02-08-2011, 02:04 PM

Quote:

close... simply evacuating the system will NOT remove but the slightest amounts of oil from a system. the only way to get oil out of a system is by flushing each component

Flushing each component and replacing anything that may be suspect to being stopped up is, in my opinion, the best way to insure you have a quality a/c system when you finish. You know exactly how much lube and freon are in the system.

I rebuilt one on a Honda a few years ago that was full of these little balls. I'm assuming it was some kind of leak stopper. I ended up replacing EVERYTHING on that system. It was interesting seeing the relief valve on the compressor lift.

leathermang · #11 02-08-2011, 02:06 PM

Quote:

Originally Posted by compu_85

Can you just leave the compressor on end for an extended period?

Can you restate that question.. not sure what you are asking...
' On end' .... ?
Do you mean just leave it in the system without taking it out.. if not using it ?

compu_85 · #12 02-08-2011, 02:12 PM

No, remove it from the car, and place it in a catch can with the ports on the bottom so the oil runs out.

-J

leathermang · #13 02-08-2011, 02:30 PM

Quote:

Originally Posted by compu_85

No, remove it from the car, and place it in a catch can with the ports on the bottom so the oil runs out.-J

Which compressor do you have ?

Is this for the purpose of ' flushing' ?

What do you consider " an extended period of time " ?

engatwork · #14 02-08-2011, 02:32 PM

Hold it where the hose connection ports are the lowest part and spin it in the direction it normally turns to remove the oil from it. There is no way to get 100% of it out.