OK earlier in 2007 I paid an AC service for a can of R12 to be added to my system. I have a small leak. Watching the process I thought "I could do this myself". Since then I have gotten my EPA card and now have R12. I have the manifold and the can tapper. I'm ready to go. Wellll, its been a year and a half and honestly I forgot which side is the high pressure and low pressure side. I've got two fittings on the acumulator (Low pressure ?), does it matter which one I connect the low side gauge to. So which is the high pressure side? Thanks

 

Can you put the gauge on either one STATIC, and then start the motor to see if it goes up or down? Check with Suncr A/C guru...

 

Some of the replacement accumulators have two low pressure test ports because they are made to fit a variety of vehicles. You can use either port. On your car one of the ports is probably blocked by the radiator. Always charge through the low pressure port.

If you look at the condenser on the passenger side you'll see two metal lines. One comes from the discharge port of the compressor. The other line is a small diameter steel line. If you follow that line it goes to the evaporator core. Not to far from where that metal line attaches to the condenser is the high pressure test port. It should have a small cap screwed over it. You may need the proper adapter fitting to attach the high pressure hose from your manifold gage to the high pressure test port.

 

I did notice that one acumulator fitting was facing foward toward the radiator. I didn't notice an adaptor for that fitting, I will check into it. I figured that smaller line was the high side. Thanks

 

You shouldn't hook them up backwards and that's why the fittings are different sizes. You'll need an adaptor for your high side and remember to keep the High Side Valve on your gage set CLOSED at all times.

 

Thanks, will probally jump on it this weekend. I will post pressures when I'm there.

 

In General, One Simple way to see which is the High pressure side vs the Low pressure side.. is the size of the hose and tubes.. High pressure will be the smaller size hose and tubes. Low pressure will use the later size tubes and hoes.

 

Also if its running, the high side is HOT, and the low side should be cool.

 

The reason you DO NOT charge through the high side is that the high pressure from your AC system is much higher(~200psi) than the pressure from your charging station(R12 can), result being that your R12 can cannot overcome the higher pressure and will not get into system, with the possible chance of exploding your can of R12.

When charging on the low side, there is still pressure coming from this port(~50psi), which is about 4 times less than the high side. To facilitate the process of charging an AC system, I always set the can of R12(or R134) in a pot of very hot tap water to increase the internal pressure in the can. You can empty a can of R12 into your system much faster this way. I usually "dip" the can of R12 in and out of the hot water at first, until most of the R12 is "pushed" into the AC system. When the can of R12 is about 3/4 empty, I just leave the can sitting in the hot water until completely discharged into the system. (also, by this time, the "very hot" water has been cooled down by the R12 can. This "coldness" comes naturally from the disharge of the refridgerant from the can into your AC system.)

 

Too much bad information. The fittings on the older R12 systems are the same on high and low sides. And true, if you get it wrong, the hose will likely blow. In my bad experience, the hose will blow before the can.

On my 86, there are two fittings. One on the drier and one on the high pressure return line. To determine what is what, keep in mind 3 places/things and the process. The three points are inside car, the compressor, and a radiating unit in front of your coolant radiator.

The R12 is gas coming from the interior of the car, is compressed into a fluid, is cooled a bit by the radiating unit at the front of the car, travels to the interior where an expansion valve allows it to become gas again. When it goes from fluid to gas, it becomes much colder. The gas is then returned to the compressor and around we go. The low pressure side is usually larger tubings, more rubber, less metal tubing, will be cold when the high side is hot. On mine, the low side is on the "drier" a large cylindrical unit.

In any event, the low side will be on the line running from inside the car to the compressor that doesn't include the cooling radiator at the front of the car. I think that radiating unit is called a condensor but I don't know why, it doesn't condense as much as it cools the fluid by radiating heat just like your radiator.

 

The fittings are not the same on the high and low sides. The hoses won't
blow up at high side pressure. The condenser does condense the hot high
pressure gas to a high pressure liquid. Did i leave anything out? benny

 

I think you could blow a hose - particularly if you're using something from a Discounter (which I do from time to time - only they start leaking at the joints usually after one or two charges and I have to chuck them out). And the hoses are the same threads, but the high side fitting will need an adaptor if you want to get a hose connected to it. Anyway, the low side pressure is 50 psi or higher at rest (assuming there's something in it), but once running, it's going to be half as much AND the low side is the suction side. That's a really big reason for charging through this port. The high side is pushing liquid - the low side is sucking gas back towards the compressor. Get it running first; ie, don't open up the low side valve until it is running - then let the system pull in what's in the can. After you get a can in it, close the valve, let the system stabilize and check both the low and high side pressures. Oh yeah, disconnect the fan switch (if '89 or below) to keep the main fan on. For '90 and above, make sure they're both cranking before checking pressures and get the throttle propped open so that it's running at 1200 rpms. Your compressor isn't at max efficiency until it's spinning at this number (actually it's going about 5 times as fast) and everything is fairly meaningless unless there is air across the condensor and the compressor is doing all that it can do. Finally, if the charge is low and the compressor is cycling, jumper the low pressure switch with a paperclip. It's isn't going to work if you don't - it'll simply suck it in and when the compressor turns off, push it back into the can.

 

Although the low side is often referred to as the "suction" side, this is a misnomer and it is never truely a suction port at any RPM, as it always maintains postive pressure at the low side valve. The reason the R12 is able to to be discharged into the low side is because the pressure in the R12 can is greater than the opposing pressure at the low side fitting(~50psi < low side < ~25psi depending on ambient temperature and RPM, or rate of compression). It is true that at higher RPM, the low side pressure decreases, which makes it easier for the R12 can to dispense the refridgerant into the system. But to call it a "suction" line would infer that your gauge would go from let's say 50psi(positive pressure) to below 0psi(vacuum or "suction") at the low side port. The entire AC system is closed and is positive pressure at any point in the system; the high side, low side, condensor, evaporator, condensor, either side of the expansion valve or oriface tube....or where ever....

I think that back in the day, someone must have coined the term "suction side" to make it easier for the laymen to understand where to put the refridgerant charge. It is an easier "concept" to view the low side as a "suction" side, as oppossed to what is really happening which is a higher pressure system(R12 can or station) overcoming a lower pressure system(low side valve on any AC system).

 

Burst pressure on a decent refrigeration hose is 4000#. I think the belt will
slip before that. Yes, the hose ends are the same. The fittings on the car
are different to keep people from harm. I wasn't questioning SunCr,
Chatmans post had some mis-info. benny

 

The hose that I reported bursting with my bad experience -- several years ago -- was the hose running from the can of r12 to the AC fitting. I assumed that it was a safety feature.

 

Whoa! Didn't know this was going to be physics course. Scientists will tell you there is no such thing as "suction" but a/c guys find it quite convenient to use that word along with pull down and a couple of others. Yes there's positive pressure on both sides, but you can't deny that a lower pressure tends to pull things toward it and the issue was that the compressor is pulling that lower pressure gas towards it in order to start the vapor/compression cycle. Without that, the pressures will reach equilibrium and nothing is going to happen - which is exactly what takes place when the compressor shuts off. I'd rather leave the real science out of this (and from some of the statements made, someone might want to retake Physics 101) - keep it simple for the rest of us - all we want is cold air!

 

PS: Negative pressure is used (what a/c guys call a vacuum) to charge a virgin system. In that case, the system is "pumped down" with a "vacuum pump" and when the appropriate negative pressure is achieved, you let it "pull in" the first can or pound without turning on anything. I think our member is starting with something in it, so we can save this discussion for when someone is starting over.

 

Uncle.....you win....now I'm off to my Physics class..