Do you need to evac the old R-134a when you recharge it? I read the instructions on a couple different cans and it doesn't say anything about this. However, I found an old thread on here from 2011 where one person said you did need to and that if you didn't you were wasting the refrigerant. So is this actually necessary? If so, why is it necessary? I'm on a tight budget and really don't want to mess anything up. Thanks y'all!!

In a perfect world, you would fully drain the system so you know exactly how much freon and oil it has, and use a gauge set to measure the pressures. I would expect an a/c repair shop to do this. If you're just trying to add some freon to get it cycling again then I wouldn't worry about it. What's the issue, btw? Not as cold as you think it should be, the compressor cycling too fast (generally more than 10-times a minute) or not running at all?

Ah, ok. For a second I was thinking I was totally misunderstanding what "evac" meant. Thanks for that clarification. The issue is that it's not very cold. It's just cool. Pretty crappy as far as temperature to be honest. I read that when you do it you should have it on full blast, with the closed cabin setting, and the doors open. Why would you have the doors open? Have any tips?

I have no clue about the recommendation to have doors open. You want it on high so the compressor is cycling and helping to pull the freon out of the can. If you put it on high with the engine idling, is it cycling on/off a lot? Typically as it gets low, it will start cycling frequently. The pressure on low side of the compressor drops quickly due to the lack of freon and the low pressure switch cuts it off. If low, you'll hear it kicking in/out every few seconds. If the charge is too low to even turn on the low pressure cutoff, it'll stop cycling altogether. If everything has leaked out, it's not cycling at all, and you have gotten air in the system, it's usually a good idea to evacuate it (suck it down to a vacuum) to get any moisture back out.

I recharged it and now it feels colder on 1 half way in the blue as it did all the way in the blue on 4. That was certainly a $20 well spent. I went from no A/C at all this morning with a failing Blend Door Actuator to a working A/C that blows pretty darn cold thanks to the folks on this forum. I'm stoked. Now I just need to get that Grand Cherokee vacuum reservoir so everything is running 100% proper. I didn't have room to mount that giant ball reservoir anywhere so I just plugged the line. I got it up to 50 and the vents didn't start to divert improperly. Maybe faster on the interstate it will though.

And yeah it was cycling a lot until I got more in it.

If you want to dive a little deeper in auto AC, a set of gauges is worth the investment. . It will let you see the high side and low side pressures. I have used this: https://www.harborfreight.com/air-vacuum-pump-with-r134a-and-r12-connectors-96677.html . with a compressor to pull a vacuum and test for leaks. I have found that the gauges that come with the recharge kits are close enough as long as your system has not completely leaked all the refrigerant. The high side pressure will tell you if you have other problems, but as long as it's just low of R134a, just reading the low side will get you close enough. I have completely rebuilt the AC system in 2 XJs with these simple tools. AC works great and have not not had other problems.

Yes! Thank you. I was watching this Chris Fix video and he had the manifold gauges, but I wasn't sure which to get. Yeah, the gauge that came on the recharge didn't have the moveable face where you compensate for outside temperature so I just waited until the afternoon when it was under 85 and did it. It was even colder this morning for some reason. I had it on half temp and at 1. You have no idea how happy I am, hahaha. I'm having a blast learning all these new systems so thanks.

If you have a gauge set, you can reference charts and diagnostics if you are having problems. As you stated it varies base don the ambient temperature. http://rechargeac.com/how-to/ac-system-pressure-chart

I already a compressor and the investment in the gauges and vacuum tool have saved me a ton of money by not having to go to an AC shop.