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newbie a/c question


NAXJA Forum User
Ok, not a mechanical or Jeep newbie, but new to my 2000 XJ with them new-fangled airbags and air conditioner thingamabobs.

Anyway, I bought the thing and the compressor clutch won't engage. Trying to get a jump on summer, I bought a kit with 2 cans of r134a, a hose with fitting and gauge, with pistol type delivery.

I cranked up the engine, put on the a/c, attached the unit as directed, and put most of the can in, until I was in the "blue" or proper range on the gauge (it was pretty much empty when I started). At no time did the compressor kick on, and the accessory electrical fan didn't come on.

As for the a/c: what's the next step?
As for the fan: shouldn't that have come on with the a/c switch?

Any help, as always, is greatly appreciated.

Tom (I did not buy the a/c for dummies kit!)
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You need to locate the low pressure switch and jump the terminals to make sure the system still operates.With a/c on, truck running jumper the terminals (paper clip works good),a/c compressor and fan should kick on. Once you confirm the system is working you have narrowed it down to either improper freon charge or possibly bad low pressure switch.these switches do go bad fairly often.If the system was completely empty, put some dye in with your freon so that you'll be able to find the leak later on. If it has been empty for a while, it should be vacced down to remove moisture.also vaccing it down you may be able to hear a leak before you waste your freon.
Thanks. So I did it ass-backwards. I'm guessing the low pressure switch is located on the low pressure line somewhere. I'll take a look at it tomorrow.

If I do have to replace that switch, does it necessitate evacuating the refrigerant to do so?

thanks again!
Thanks again. Is it possible, since the compressor is not operating, that I still don't have enough refrigerant in there, since the system isn't pressurized?
Will the comp kick on when you jump the switch? Yes if you don't have enough freon it won't run but if you got it to take a whole 1lb can, I would think it should probably at least try to cycle.If its not the switch,Your best bet is to vac the sys. first. It will remove any moisture and the vacuum will help draw the new freon in. You said it was empty right? Unless someone took it apart to work on the vehicle,I would almost garantee you have a leak. Putting it under vacuum will give you a chance to see if it will hold pressure before you put freon in. Just vac it down for 15-30 mins. shut pump off let it sit awhile and make sure gauge hasn't moved.You can rent a vacuum pump if you don't have one, or with spring coming start looking for a shop running a a/c recharge special r134 won't be that expensive
Ok, I couldn't figure out which switch was which, and I didn't want to screw around...too much. I got the gauge back on the low pressure side and it was below optimum, so I decided to fill it to the upper limit of the "charged" zone on the gauge. The compressor started cycling. When it did, it would push the needle down; I kept adding until the can was empty. The cycling stopped, and so did the compressor! The air never blew cold, but I couldn't detect a leak inside the cabin or out with the black light. When I shut 'er down, the needle was firmly inside the "green" zone on the gauge, but no compressor activity. Does sound like a monster leak, and from all accounts I should bet on evaporator, but I didn't see a yellow leak anywhere.....
i would buy another can and add a little more. i had this problem when i bought my 97 and it took a whole can right off the bat and still no cold air, and the compresser would cycle. so i got another can and it took half of that, compresser stays on and wal-la cold air. aint had problem since.
Also, when servicing with the little 1lb cans, its good to have a bucket of very hot water.

The can will only empty as much that will equalize pressure between the can and system. It takes as much as an hour for pressure to equalize just in the AC system when its off, and pressure in the can only increases as the refrigerant boils. So its possible, if you don't take your time, while the compressor is NOT running, that a lot of the refrigerant gets left in the can.

Drooping the can in a bucket of very hot water helps boil the refrigerant and increase its pressure and get it into the system faster.

Once you get the compressor running, the pressure on the low side drops to ~27PSI, and pumps thru the new refrigerant so pressure doesn't build and prevent it from flowing out of the can, even then, a bucket of hot water helps get as much out of the can as possible.

Without the compressor running, it can take an hour with a bucket of hot water to get the can to empty most of its refrigerant.
From one who has a 98 and had problems from day one when it was new. The dealer topped off my A/C 3x and it took about 5 months to leak down. After the warranty was over and I had to do it myself I found the leak, the leak is in the evaporator in the heater box and I need to replaced it.
However I did live with the leak for about 4 years just topping it off every spring till it reached a point it would not take any more 134a, there was air in the system. I vacced the system down with a sun a/c station and refilled with 134a with yellow dye in it, refilled it twice before we found the leak, we could see yellow dye coming out of the drain pipe on the firewall but it took a few weeks, I imagine the evap is probably coated with the dye. It's going to get done next month. The entire dash has to come out so I'm also going to replace the heater core.
97XJ Jeeper said:
i would buy another can and add a little more. i had this problem when i bought my 97 and it took a whole can right off the bat and still no cold air, and the compresser would cycle. so i got another can and it took half of that, compresser stays on and wal-la cold air. aint had problem since.
Thats the funny thing about r134. Not enough and it will blow warm (provided the low pressure cut off switch hasn't kicked in). Too much, and it will also blow warm. Gotta hit it just right, and it's real picky too. Doesn't take much variation to throw it off.

Had to recharge mine last year, and it held it's charge fairly well through out the summer. I did top it off once before I went on a 4 hour ride to the beach in 100* weather. A/C worked pretty good considering the situation (high ambient temp, no tint on windows at the time, 2-3 people including myself, and 90% of everybody's crap loaded down in the back). Will be interesting to see how it does this summer now that I have tinted windows.