DIY Air conditioning,trobleshoot an repair, where to start?

[rooster]

I have several cars that have AC that dont work, generaly if the ac quite working we didnt
get it fixed somewhere, I have had a buddy add freon to my pickup just to leak away a
few days later.

For fathers day the kids got me a Harbor fright  a/c manifold gauge set (R134A)! Sence
there cars dont have working AC I guess this made sence , if I knew what to do with it.

The instructions that came with the set dont say very much, but from what I can see the
guages will tell if there is freon in the system , and you can add freon with the use of the
set.  Input wanted.

[enjenjo]

You can use the gauges for more than that. They are useful as a diagnostic tool, the pressures can many times tell you what the problem is. There are several AC troubleshooting sites on the net that can help you decipher the pressure readings. The only other thing you might need is a leak detector.

[GPster]

Going back to the days of R12, I used to find that a system that wasn't running would egualize (same pressure on both discharge and suction of the compressor) at maybe 65#. wHILE IT WAS RUNNING THE SUCTION SIDE WOULD BE PULLED DOWN TO 35# (cap lock and I'm not going to re-type) and the dis-charge side would start running  at 150#. Most of the leaks I remember were at the crankshaft seal of the compressor and they would leak when the system was not running (65#) which would let the equalization pressure  be low and  make the running pressures be lower. Now if the equalization pressures were low or 0# when the compressor was run the suction side of the compressor would drop to a negative pressure and if it was the compressor seal where the leak was (and the crackcase of the compressor is usually the suction side of the system) running the compressor would have allowed the system to suck in air. Air doesn't condense under pressure like refrigerant does so discharge pressure may  climb to above 400# when the system is  trying to run. That would require pumping a vacuum on the system and starting over which should be done anyway with changing to R134. Part of the atmospheric problem with R12 is that it used to be so cheap                    ( commercially $.48 per Lb. in quantity) that it was just cheaper to throw itat the problem and  than figure out what the problem was. Like Frank says, the gauges will help you know that there is a problem but you should have a leak detector (halide torch?) to find out where the problem is. Now a lot of automotive systems have a safety on them to keep things from getting that bad. A low pressure switch to keep the system from running in a vacuum and sucking air into itself and high pressure switch to keep the system from blowing itself apart. There are people here that can hazzard a quess or make suggestions on what to do next now that you can tell them conditions and pressures. GPster

[rooster]

Im looking at doing 3 cars:

95 GMC pickup 134A
knowen to have leaked freon
Compressor does not kick in
I got zero reading from high and low side from gauges (not running)

94 olds cutless 134A
condition unknown
Compressor does not kick in (metal shaving in the compressor clutch area)
I got zero reading from high and low side from guages (not running)

95 Mustang 134A
I replaced the compressor last winter ( used junk yard compressor), replace oil and 0rings, did not re-charge system
I did not hook the gauges to the system for a reading!

None of the hoses show any sign of where it may have been leaking (greasy spot)

From here my best guess is to assume thay are going to continue to leak, is it best to replace the dryer and orfice, 0 rings then charge with 1 can of freon and use a detector before I continue any feather re-charge? Should I use a can with red die in it?

[tomslik]

Im looking at doing 3 cars:

95 GMC pickup 134A
knowen to have leaked freon
Compressor does not kick in
I got zero reading from high and low side from gauges (not running)



most likely a compressor case leaking

94 olds cutless 134A
condition unknown
Compressor does not kick in (metal shaving in the compressor clutch area)
I got zero reading from high and low side from guages (not running)


this'n sounds like the clutch took a dump and maybe got the seal, too.
(another compressor)

95 Mustang 134A
I replaced the compressor last winter ( used junk yard compressor), replace oil and 0rings, did not re-charge system
I did not hook the gauges to the system for a reading!

gauges ain't gonna help ya much with an empty system

None of the hoses show any sign of where it may have been leaking (greasy spot)

From here my best guess is to assume thay are going to continue to leak, is it best to replace the dryer and orfice, 0 rings then charge with 1 can of freon and use a detector before I continue any feather re-charge? Should I use a can with red die in it?

[rooster]

The wife came home with the 95 olds we have that has the AC still working, I hooked up the gauges to see what I could get , with the engine not running, I came up with +27 on the high and low side.

I havent found any info on what the reading should be under any test, I have looked under the hood and in the hayes manual. The directions hat came with the gauge set dont even show how to add a can of 134A.

Other news is a buddy down the street has a vacume pump and a leak detector. I have some more net searching to do, before I do anything.

Thanks for the input , keep it coming.

[58 Yeoman]

I've never used it, but they also have freon with a dye in it to help find leaks.  If you use an old style torch, don't breath the fumes, as it'll be phosgene gas.

[enjenjo]

Checking with the engine not running is of no use, other than to say there is something in there. The pressures with the engine running mean something. Generally the pressures with it running at idle will be about 20 to 30 psi on the low side, and 150 to 200 on the high side, but depending on ambient temperature, they may be higher or lower.

Also R134 is sensitive to overcharging, so it really should be charged by weight, rather than pressure. And of course to charge by weight, you have to know how much is in there to begin with. So a complete recharge is generally no problem, but "topping off" can be hard.

Technically you shouldn't charge R134 into a system with a known leak, it's against federal law. When I was doing AC work, we charged with nitrogen, and used a sonic leak detector to check for leaks.

http://www.autoacsystems.com/

http://www.icarumba.com/icarumba/resourcecenter/encyclopedia/icar_resourcecenter_encyclopedia_ac1.asp

[GPster]

I havent found any info on what the reading should be under any test, I have looked under the hood and in the hayes manual. The directions hat came with the gauge set dont even show how to add a can of 134A.

Your gauge set is probably somewhat standard but the gauges have a scale on them for R134 rather than other refrigerants. The outer reading on the gauge should be actual PSI and the other set of readings on the gauge face are actual temperatures. That scale is sometimes colored and the refrigerant that refered to on that scale is usually colored the same. The manifold that holds the gauges usually has 2 valve handles and three hoses. The center hose on the manifold usually is for the supply from a storage tank to the manifold. The left hose (sometimes blue for cold) is for the suction side of the system or the hose coming for the evaporator coil under the dash to the compressor. The gauge on the right side of the manifold is of a higher scale and is to show the discharge pressure of the compressor to the condensor, the coil in front of the radiator. The gauges will read with the valves closed if there is pressure to the hoses with either the valves open on the compressor or if there aren't any valves the ends of the hoses will/can compress tire valve like cores in the compressor gauge access fittings. I'd quess that that system is low on refrigerant and that the compressor may start but shut off as soon as it pulls the pressure down. 27 PSI should be enough to check for leaks  before adding any refrigerant and if a low pressure swicth is keeping the system from running than maybe it hasn't pulled air into the system. If you can find a leak and fix it and add refrigerant you would probably be adding refrigerant while the system is running to show on the gauge a coil temperature of 35 degrees or so and the suction line to the compressor getting somewhat cold. I don't know much about R134 but if the high side gauge reads a temperature much higher than say 130 degrees you may have air in the system. The more I type the more I can't understand myself so start with this and ask more questions. If I'm totally off the wall someone will correct me. GPster

[rooster]

Thanks for the info and great links!  Its still sinking in.

Joe the gauge set I have has a sight gauge built in it, from what I understand if you see bubbles in it , that would indicate you are low on refrigerant.

[GPster]

Thanks for the info and great links!  Its still sinking in.

Joe the gauge set I have has a sight gauge built in it, from what I understand if you see bubbles in it , that would indicate you are low on refrigerant.

A sight gauge will only tell you if you have flow through it. I could only think it would tell you if your refrigerant tank goes empty while you're trying to charge the system. If you have a sight gauge on the system and you see bubles in it when the system is running that would be an indication that the system is low on refrigerant but if the system is air-logged you can keep adding refrigerant and find yourself with 400 PSI of head pressure and still be trying to stop the bubbles. GPster

[Ed ke6bnl]

Thanks for the info and great links!  Its still sinking in.

Joe the gauge set I have has a sight gauge built in it, from what I understand if you see bubbles in it , that would indicate you are low on refrigerant.

A sight gauge will only tell you if you have flow through it. I could only think it would tell you if your refrigerant tank goes empty while you're trying to charge the system. If you have a sight gauge on the system and you see bubles in it when the system is running that would be an indication that the system is low on refrigerant but if the system is air-logged you can keep adding refrigerant and find yourself with 400 PSI of head pressure and still be trying to stop the bubbles. GPster

air will give you a higher head(high side) head pressure while the discharge will not get any hotter.  most have safetys for both high and low pressure.