Every two years I have to have a freon boost in my truck to keep it blowing cold. Now that its hit the triple digits here, its time again. Earlier this year I was cleaning out a rental property and found these gauges and a tank of freeze 12. Problem is I have no idea how to hook up the gauges or read them. Can someone help me out please? I see which scale to read the R 12 on, but thats about all I know.

TIA

Curt,
How you set the gauges up depends on how you want to use them. If you're filling, you need a third line or to plug one of the outlets at the bottom. If you want to read the high and low sides, you hook each up to the appropriate line and the outer two nipples on the manifold body (the thing the gauges are attached to). You would still need to plug the center fill nipple. Readings from each are dependent on vehicle type and charging system. I'll get back to you on "correct" numbers. I can also give you a more thorough walk-through when I get home from work, but there are several good walk-through videos on youtube as well. You will most likely need a couple more parts to get this working correctly. Or, HF has a decent complete set for like 40 bucks, if I remember.

-George

Ok, I understood that. I think. So, the red gauge is the high pressure side and goes to the valve closest to the accumulator?

Yes, theoretically. I can't tell if this is a 134A set though. 134 and R-12 have different size ends, and will not interchange. Also, a high side and low side are different fittings within each type of system too, so you can't get them backwards. On second look, I think the three dummy nipples at the top are what you would use to block a hose off. So all you really need is one more hose, if you're using it to fill. If not, you could also just use one of the cheapo fill kits from any APS and the kit just to check low/high pressure. The car needs to be running with AC on to get accurate readings, by the way.

Its an R 12 system

The three "dummy" nipples are where you connect the hoses when not in use (coils them up).

Red hose is generally hooked to the high pressure gauge.

Blue hose is generally hooked to the low pressure gauge.

A yellow hose is generally hooked to the center tap and is for filling the system from a can or ???

That said, you only need two hoses ... one to the low side and one to the can. The high side valve can be closed.

All pressures shown on the gauges are temperature dependent, so you need a pressure / temperature chart associated with the refrigerant you are using.

When filling a system on a hot day, we would generally have a blower to blow air thru the condenser. If we didn't have that, we would run water from a hose on it.

High side pressures with R12 can hit 400 psig. Low side pressure would be in the 40 psig range. The pressures, again, are dependent upon ambient air temperature.

Anyway, that's what little I remember from my A/C days.

If you put freeze 12 in it, be sure to label it somewhere obvious. It will contaminate an R-12 or R-134 machine and cost the next service guy MAJOR bucks. Most A/C guys won't touch that stuff.

The Cap'n

Ok, thanks guys. I'm an expert now! LOL. We have coolness. I need it, its 106 today. Weeeee!

Thanks for the heads up Cap'n. I'll make a tag to attach to the low side schrader. No one will be working on it but me, but I'll do it anyway.

See, I knew someone would clear up my inadequacies. Yeah, sorry its been some time since I've done any A/C work, but I taught myself. You only need two hoses if you're only filling and checking one side at a time. You will need an adapter with the needle valve on it to connect to the hoses, then the can itself. I think these fit both R-134 cans and R-12, again, available at most auto stores.

Be sure of two things:
If the system hasn't discharged already, PLEASE get it discharged at an A/C shop. Most of them do it for free since they can re-sell/recycle the coolant back to manufacturing companies. Its something like a 4,000-10,000 fine if you get caught venting it. And humor the tree-huggers like me, it makes me happy that we're not venting GH gasses out needlessly (we lose enough already from normal leakage in A/C systems).

You also want to vacuum the system out before refilling. Need a compressor and a Harbor freight vacuum inverter. They're cheap too, like 10 bucks. You hook it up to the compressor, then the gauge manifold and then the system. This sucks out any air and water vapor in the system. While the vacuum is still attached, you shut off the compressor and close the valve to the low side. Attach the can, and puncture it. Open the valve from the can to the manifold. Then, loosen the hose going into the manifold for a split second, which will purge anymore air/WV trapped in that line. Close it, then re-open the valve to the low-side with the car running. It should start sucking in the R-12. Can should be upright as much as possible, but in order to get it going, you might have to liquid-fill it with the can upside down for a bit, but NOT the whole time. Eventually the compressor will kick on and assist in the process.

Last note, if the system is running fairly well and you didn't replace any components, I'd suggest making sure you only buy straight coolant. If you get the coolant/oil mix, you're adding unnecessary oil to the system, which throws off the ratio. Too much oil, not enough coolant and you don't get cold air.