AC recharge question - JeepForum.com
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post #1 of 29 Old 04-02-2020, 11:01 AM Thread Starter
KiloWatts
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Hi all, I'm hoping someone can steer me in the right direction here. My AC clutch was not engaging. I jumped it at the plug and it works fine, so I believe it's low on refrigerant.

When I hook up the gauge to the low pressure line while the compressor is running, it reads 0. I crank the refrigerant can to full blast and it barely moves the needle. When I shut off the compressor it reads about 40psi. I don't want to overfill it, but I'm unsure if I should be letting it continue to fill or not (the line gets incredibly frosty - I don't know if that's supposed to happen or not).

After I added a bit, the clutch does automatically kick on and it blows cold air, but it only kicks on for a few seconds at a time. I need to know how long this process usually takes, and if I should pull up a chair and leave the can connected for a while.

Any advice would be helpful. Thank you!


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post #2 of 29 Old 04-02-2020, 10:20 PM
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How much does a proper A/C recharge cost there in the USA? If the system is empty enough for the compressor to not run at all, vacuum pull is needed to remove any air & moisture from the system - and preferably also replace the receiver/ dryer.
Doing the vacuum pull shows any larger leaks so you know if it's even worth filling up the system. If you want to do a proper leak test, use compressed nitrogen and fill up to something like 300PSI and use soap water to check for leaks. You can't check the evap core though..

Full system charge for a ZJ A/C system IIRC is 26oz or 28oz and 7.5oz PAG100 oil; however you only add the amount of refrigerant oil that comes out with the vacuum pull. There is a chart in the FSM that shows how much PAG oil you add into each new A/C component when replacing them.

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post #3 of 29 Old 04-03-2020, 12:01 AM
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0 psi on low side when compressor on & some reading when compressor off could mean you have a blockage in the system. You need to get a proper gauge set that reads the high side as well and do not add any refrigerant at this point. If pressure is through the roof it would be normal for high side pressure switch to shut off the compressor. See what happens on both sides.

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post #4 of 29 Old 04-03-2020, 07:44 AM
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When I replaced my A/C and recharged my system I followed the FSM and I used my vacuum pump and gauges to verify zero leaks when the vacuum is maintained.


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post #5 of 29 Old 04-03-2020, 12:09 PM
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When the compressor is OFF, it should read up around 80-100 psi. Add until the compressor stays on and then maybe another squirt and call it good. Add for a couple seconds at a time. It takes longer, but its more accurate. Make sure your low side cap is tight. Hand tighten as much as possible and then I usually give a LITTLE more with a pliers. Make sure the plastic cap on the compressor is tight also.
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post #6 of 29 Old 04-03-2020, 12:22 PM
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The last time I had my A/C system vacuumed and refilled from completely empty it cost me ~100 - which is about 110$.
How much do refill cans cost there in the USA, or how much do shops usually charge for an A/C refill with an "idiot machine" (plug in the lines, press the run button and it does the job)?

We don't get to buy refill cans at all at auto part stores, they are illegal here so all air conditioner refills/ service personnel need to have a license to perform any type of work on the system. Sort of stupid, with the fairly low prices I don't really see it being an issue.

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1990 XJ Limited (4-door), 4.0 I6, AW4, NP242, ***rolled and totalled @ 165k miles***

***Under construction***
1990 XJ (4-door), 4.0 I6, AW4, NP242, PBR 42" tires, Unimog 404 portal axles, 110" WB, full cage + uniframe completely rebuilt, front 3-link + panhard / double triangulated 4-link rear,... ***SOLD***
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post #7 of 29 Old 04-03-2020, 12:54 PM
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Quote:
Originally Posted by StPaul59 View Post
When the compressor is OFF, it should read up around 80-100 psi. Add until the compressor stays on and then maybe another squirt and call it good. Add for a couple seconds at a time. It takes longer, but its more accurate. Make sure your low side cap is tight. Hand tighten as much as possible and then I usually give a LITTLE more with a pliers. Make sure the plastic cap on the compressor is tight also.
He could have a stuck TXV valve/orifice tube and the pressure will never equalize between the low and high side. The low side should never go to zero! If he keeps adding without monitoring the high side, he can burn up the compressor or burst the discharge line.

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post #8 of 29 Old 04-03-2020, 01:04 PM
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It would suck having to sit on the Group W bench, next to the father rapers, for having purchased a can of R134a. I got four cans of DuPont Suva R-134a A/C refrigerant for $18 four years ago.


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post #9 of 29 Old 04-03-2020, 04:34 PM
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He could have a stuck TXV valve/orifice tube and the pressure will never equalize between the low and high side. The low side should never go to zero! If he keeps adding without monitoring the high side, he can burn up the compressor or burst the discharge line.
I assumed it was zero because of years of it not working. Mine was when i bought it 7 years ago. It sounded like the pressure came up as he added to the system. I figure if anything blows, it needed to be replaced anyway.

The correct way is to have a shop recharge the system, but there are cheap ways to get it working.. Problem is when you don't know where it's leaking you never can keep it working correctly, and finally out of insanity to crack and turn to a professional to fix it.
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post #10 of 29 Old 04-06-2020, 05:13 PM Thread Starter
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you never can keep it working correctly, and finally out of insanity to crack and turn to a professional to fix it.
Ah, my modus operandi!

I managed to get it up to 20psi after two cans. Something's still not right, but I have cold air again. When it stops again I'll take it in, provided the plague is gone by then.

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post #11 of 29 Old 04-06-2020, 06:26 PM
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Ah, my modus operandi!

I managed to get it up to 20psi after two cans. Something's still not right, but I have cold air again. When it stops again I'll take it in, provided the plague is gone by then.
Depends how big the cans are. The ZJ holds a lot of refrigerant. Most cans are 10oz. The zj is up around 28-32oz I think. It should say above the radiator what the capacity is. You're probably a can short. How warm is it there?
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post #12 of 29 Old 04-07-2020, 08:27 AM Thread Starter
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It was 65-70 yesterday. The Haynes manual says 28oz and I put in two 12oz cans. Still, I never really saw the needle move during the process. During the first can fill it hovered around 10psi. Then I turned off the car and gave it a break. When I put on the new can, the needle showed around 20psi and stayed there the rest of the time while I emptied the 2nd can. All of this was done while the compressor was on - I jumper-wired the plug.

So, not quite how I expected it to go.

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post #13 of 29 Old 04-07-2020, 08:35 AM
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Was the system evacuated of air, water vapor and other contamination as the first step?

Was the evacuated system verified to hold / maintain a vacuum, as an indicator of no leaks, for an extended period as the second step?

Is a standard two-gauge manifold set being used to perform the hi side / low side readings?


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post #14 of 29 Old 04-07-2020, 09:41 AM
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Originally Posted by KiloWatts View Post
It was 65-70 yesterday. The Haynes manual says 28oz and I put in two 12oz cans. Still, I never really saw the needle move during the process. During the first can fill it hovered around 10psi. Then I turned off the car and gave it a break. When I put on the new can, the needle showed around 20psi and stayed there the rest of the time while I emptied the 2nd can. All of this was done while the compressor was on - I jumper-wired the plug.

So, not quite how I expected it to go.
Don't jump the wires, it will kick on when there's enough pressure. It's designed NOT to run if pressure is low otherwise you could burn up the compressor. Keep in mind you will only get about 80% of the contents out if the crap cans. Youre still low. To be safe just add enough to get the compressor to stay on, that's the safest most accurate hack way of doing it.

I would strongly recommend replacing the dryer/accumulator before the shop fills it after everything checks out.
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post #15 of 29 Old 04-07-2020, 09:43 AM
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Originally Posted by wingless View Post
Was the system evacuated of air, water vapor and other contamination as the first step?

Was the evacuated system verified to hold / maintain a vacuum, as an indicator of no leaks, for an extended period as the second step?

Is a standard two-gauge manifold set being used to perform the hi side / low side readings?
Nope. He's just trying to get it running and eventually he'll take it to a shop.
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