Auto Techs, help

[SpinnerBait_Nut]

Ok, you auto tech gurus out there, I have a a/c question.<br /><br />I have worked on cars/trucks the biggest part of my life, but not much on A/C units.<br /><br />I just got a 1996 Jeep Cherokee and noticed the a/c was not working.<br /><br />It is the R134 system.<br /><br />I thought maybe it was low on R134 so went out and got some, added one can, but still no compressor kick on.<br /><br />I unplugged compressor and hook a jumper from battery to it and it came on and started cooling.<br /><br />I disconnected it right away cause I did not want to do any damage to it.<br /><br />Now, I checked all the fuses/breakers it has for a/c and all were good.<br />Even checked breakers with ohm meter to make sure none were open and all checked ok.<br /><br />Now, what should I look at next?<br />Pressure switch or what?<br /><br />Thanks in advance.

 

[SS MAYFLOAT]

Re: Auto Techs, help

SBN, First you need to know what the capacity your system holds. Usually a sticker somewhere around the engine compartment. It is possible if your system was completely empty, 1 can may not be enough to raise your suction pressure high enough to kick on you compressor. You need to find out where your low pressure switch is. Unhook it and take a contunity check. If it is closed then the pressure is high enough to kick it on. Open reading means it will not allow the comp to kick on. Usually indication of low refrigerant. <br /><br />Now if your system has leaked out all of the gas, you need to find the leak and make repairs. If it has a real slow leak that takes a year to leak out, a recharge can get you by again. But you will need to pump the system down with an evacuator (vacuum pump). If it has a filter drier, it should be changed also. R-134 is natorius for absorbing moisture in the oil. SUCKS. Refrain from having the lines open for over 15 minuets. The oil is that bad for attracting water. It will freeze in your expansion valve and keep it from working.<br /><br />But you must pull a vacuum on the system. If you don't, you will cause a very high pressure on your high side of the system. Can blow "O"Rings, lines, and even the condenser. A set a guages tells ya alot on what your system is doing.<br /><br />If I waa in your area, I would drive over and give ya a hand. Hope this helps....SS

 

[bubbakat]

Re: Auto Techs, help

SBN I would say check the expanson valve<br />put a wet rag over thevalve and kick it on and let run that will tell it

 

[SpinnerBait_Nut]

Re: Auto Techs, help

Let me say something else about this.<br /><br />When I look in the site glass, I can see some movement in there even when the compressor is not on.<br /><br />It's not like it's plum empty.<br />That is why I thought maybe it just needed a little add on.<br /><br />Thanks

 

[SS MAYFLOAT]

Re: Auto Techs, help

Sounds like it was empty to me SBN. The movement that you see is the gas you put in earlier. The gas will equalize and move around as the outside air temp changes.

 

[SpinnerBait_Nut]

Re: Auto Techs, help

I.m sorry SS, that was before I added any without the compressor running, I seen movement.<br />My bad

 

[SS MAYFLOAT]

Re: Auto Techs, help

I still think your real low. But not having guages on the system it is hard to say. Need to know what your pressures are......SS

 

[SlowlySinking]

Re: Auto Techs, help

Hi SBN, try<br /><br /> http://www.aircondition.com/ <br /><br />Lots of info, good luck, Ken

 

[JasonJ]

Re: Auto Techs, help

I have a 93 Grand Cherokee Limited, and all my R134 leaked out. I got one of those gauges and it took three big cans to get it up to the proper pressure, and it has been fine ever since. The Jeeps are notorious for losing the R134. They are also notorious for the ECM going out. I just spent $1200 for that little gem. Stock radio blew up, speakers died. Brakes warp all the time too, and we won't even get into the leaky transfer case. Thats okay, the Jeep belongs to the missus, my Ford F150 has worked just fine, just fine......

 

[SpinnerBait_Nut]

Re: Auto Techs, help

Well this '96 has got just over 86k miles on it and I got it from the original owner, but he never said anything about tha a/c

 

[Skinnywater]

Re: Auto Techs, help

Without guages your chasing your tail. Continueity checks on pressure switches is great as long as you know what pressures you have in the system.<br /><br />The pressure switch is but one item that commands the compressor clutch. Since you've fired up the compressor you've eliminated the clutch or compressor as faulty. However, you've bypassed everything else in the compressor command. A/C switch, thermostat control, evaporator temp sensor, A/C relay, low/high pressure switch, wiring and fuses all have been bypassed.<br /><br />A couple things I can suggest.<br />Carefully follow the system visually. Pay particular attention to hose connections/fittings and high side components and the expansion valve.<br />Look for oily greasy stains as this will indicate the likely source of a leak. The compressor may have clear light oil hanging off the bottom of it. The condensor will have a greasy dirty stain on it.<br />A set of R134 guages can be had for $75 if you shop around. However, simply charging an empty system without evacuating creates inefficientcy, overheats the compressor and corrosion and will ruin a system internally.<br />Don't be adding oil to the system unless you replace a major component, compressor and drier or condensor.<br />As with an engine or transmission, the A/C system will be far better off slightly low on oil then slightly overfilled.<br /><br />BTW, checking A/C compressor command on a lot of systems in defrost mode will bypass most sensor chains, helping in diagnosis.

 

[SpinnerBait_Nut]

Re: Auto Techs, help

Thanks all.<br />I have checked all the fuses and breakers for the a/c system and they are ok.<br /><br />It does not matter if on a/c mode or defrost mode, the compressor will not kick on.<br /><br />I will check other switches tomorrow and see what I find.

 

[backdraft]

Re: Auto Techs, help

Spinner, The compressor will not come on until there is sufficient freon in the system. This is to keep the compressor from burning out. You need at least 3 cans. When you look through the sight glass, and it is properly charged , you will see small bubbles passing by the glass. A lot of bubbles means still not enough freon. Very few bubbles usually means overcharged. There is a pop off valve which will go off scaring the crap out of you on some units.nevjb

 

[SeaMasterZ@aol.com]

Re: Auto Techs, help

SBN, get you a kit (19 oz cannister) with a guage attached, run ya 22 bucks at Schlep Boys or AutoZone, whichever chain ya gots down thar - that will give ya low side pressure, which should be 25 or so<br /><br />but really you should get her sucked down and dried out, then tank er back up<br /><br />the system wont fire without sufficient pressure<br /><br />good luck!

 

[SpinnerBait_Nut]

Re: Auto Techs, help

Well, guess I will take it the experts.<br /><br />I checked and all continuity(sp) is fine.<br /><br />I am getting no voltage from the pressure switch plug on either side.<br /><br />I guess it's back up the system further.<br /><br />I'll let them find it.<br /><br />Maybe the switch in dash itself.<br /><br />Dunno, but it blows real cold when I kick it on manually.<br /><br />Thanks guys.