AC consult needed

The AC in the Jeep works great when you're at speed but barely cools in town. Gauge readings at 90-95F look like this:

Am I correctly reading this to say it has 70psi on the low side and 375 on the high? Like its massively ovefilled?

I am not an a/c expert.

If you are running R134a it look like  20psi on the low side and ~82psi on the high. 

those numbers are actually *C+20 and *C+82 according to the gauge face (if I'm reading it right), so 52psi and 114psi respectively at 32*C...but that would mean the high side gauge isn't able to read the 250psi that is expected at 32 degrees C...?

I don't know about the pressures, but working fine on the road and poorly at idle sounds like it needs more airflow across the condenser.  Does the Jeep have a secondary AC electric fan?  Is it working?

Single mechanical fan, full shroud, new thermostatic fan clutch. 

Here's a close up of the gauge. The markings are unlike the others I've seen. I think the psi readings are the the center black scale, right? 

That's the most overcomplicated gauge set I've ever seen. It looks nothing like my harbor freight set. I'm not certain of this without consulting a table or doing the thermo calcs, but I think they're trying to deduce the refrigerant temperatures from the pressures. If that's the case then your low side pressure, which is actually pretty high at ~70 psi, would give you a refrigerant temp going into the evaporator of about 20C or 68F, which is also much higher than it should be. By the same logic the high pressure side would be 82C or 180F. No idea if this is correct though. I agree it looks like it may be overfilled or having some kind of airflow problem.

Also can you quantify "works great"? Maybe with vent temp readings or even better if you could get temps of the evaporator under various driving scenarios.

In reply to freetors :

Okay, your assessment matches up with what I thought I was reading. I don't have any temp readings on the vents but when cruising it's painfully cold. Because the heater core is disconnected all I have is full cold if the ac is on, and it gets uncomfortably cold after a while.

The back story is that I found out the quick connects on my gauges were blocked up and I think I was adding freon based on bad readings. I replaced the QCs and these are the readings now. I suspect I overfilled it.

The trans cooler does leak on the ac condenser out front and attracts dirt, so I do need to check and see if its clogged. But I'm about to replace that cooler, and I'll clean it all well when I do.

If the compressor is running in those pics you are overfilled.  General  hillbilly consensus is set the low side PSI to ~35 and rock on unless you want to evac the whole system and charge by weight.  

Low side pressure in PSI with R134 correlates pretty close to evaporator temp in degree F - so set it slightly above freezing for some ice cold A/C.  If you set it on a 95 degree day, expect some icing and poor performance on a humid 70 degree day.  

You can also charge till the inlet to the evaporator in the engine bay is "beer can cold" and the clutch stops cycling.  That will get you pretty close.  

Update. I recovered a bunch of freon from the system. The gauges now read 55/250 with the compressor running and a 90*f ambient temp. And the interior vents blow lukewarm, much warmer than before. It barely cools at all even when on the road and moving. I did check my wife's car and verified the gauges are reading correctly. 

I see 3 possibilities. 

The ac clutch is slipping. Doubtful, I replaced it last year and it seems to lock up as it should. Any easy way to test it?

The compressor has failed in some unusual way.

The orifice tube is blocked.

What do you guys think?

55 is still pretty high for the low side.  Do you have the factory service manual for the ZJ?  The pressures in their charts are not the same as on most generic charts.  If you need a copy of the FSM, let me know.  

I'm swooping in for the hijack. 

I just decided to play with trying to make the AC on my '71 Galaxie wagon, which I acquired in December, work. The PO reported that the system had been converted to R134A, and it has a quick disconnect on the suction side of the compressor. I currently have installed approximately 56 ounces  of 134 into that hole, and the el-cheapo gauge on the trigger valve doodad says that the suction side pressure at idle is 25. The pressure drops at increased RPM. The green range is 25 to 35, and the indicators on the twisty lens thingy seem to indicate that it wants more refrigerant. The sight glass hasn't shown a bubble yet. The vents blow slightly cool at any ground speed, probably because this bitch has a solidly mounted fan and a full shroud. 

Should I keep adding 134? Should I run away screaming? Please advise. 

rslifkin said:

55 is still pretty high for the low side.  Do you have the factory service manual for the ZJ?  The pressures in their charts are not the same as on most generic charts.  If you need a copy of the FSM, let me know.  

I actually remembered I had those manuals and printed out the HVAC section. Tonight it was 80 degrees outside and my pressures were reading dead in book spec - 40/240 - but the interior vent wouldnt get below 60.  It's a moot point. I went ahead and ordered everything in the system except one hose. Checking the kit box on Rock Auto got me compressor, clutch, tube with integral orifice tube, dryer, and O-rings for under $200. Added a condenser for anothe $60. Living in GA makes that a small proce for ac.

snailmont5oh said:

I'm swooping in for the hijack. 

I just decided to play with trying to make the AC on my '71 Galaxie wagon, which I acquired in December, work. The PO reported that the system had been converted to R134A, and it has a quick disconnect on the suction side of the compressor. I currently have installed approximately 56 ounces  of 134 into that hole, and the el-cheapo gauge on the trigger valve doodad says that the suction side pressure at idle is 25. The pressure drops at increased RPM. The green range is 25 to 35, and the indicators on the twisty lens thingy seem to indicate that it wants more refrigerant. The sight glass hasn't shown a bubble yet. The vents blow slightly cool at any ground speed, probably because this bitch has a solidly mounted fan and a full shroud. 

Should I keep adding 134? Should I run away screaming? Please advise. 

I'd add.  

To the original poster's point, i think you probably have a condenser problem. It could be airflow related, such as a fan issue or an air blockage like you mentioned.  Pressure and temperature are related and your high side reading can be pushing up your low side readings even if the system is not overcharged simply because the refrigerant passing the orifice into the low side of the system is hotter than it should be. I would spray the condenser with a water hose while the system is running and see what your low side pressure does in that situation. You may find that once the condenser is actually shedding enough heat that the low side pressure will drop to normal or below-normal pressure (maybe undercharged now as you said). If your running pressures are goofy, you can still use static pressure (when the compressor is off for a while) to ballpark whether you've got a proper charge. At the 90+ ambient temps you mentioned, you should have something like 100-110psi static pressure when the system is off.  Just keep in mind the ambient temp in the engine bay where the ac system lives is higher if you've just turned the engine off and it's radiating a ton of heat. Under those circumstances the static pressure may show 110+ and drop as the engine cools, so it's easiest to look at static pressure when the engine is cool.

Static cold pressure is about 100psi. I think you may be right about the blockage. But I since I ordered all the parts I'm less concerned about diagnosing which ones the issue, lol.

In reply to ultraclyde :

Funny, mine behaves the same way (can't get vent temps much below 60) but still cools the Jeep down decently and makes plenty of condensate (and that's after replacing most of the system).  I'm pretty sure in my case that the temperature select door in the HVAC box isn't sealing and is letting some air through the heater core (as the A/C is colder before the engine is warmed up).  

Huh. The truck cools down out on the road, but if you drive across town after work in traffic it never really does.  Although my heater core is bypassed, so not actively hot.  I've got the heater core, ac evaporator, and blend door actuator motor coming as part of the rebuild so I'll check the seals while I'm in there if I can. Very weird, but that's kind of typical in an old system. At least I'll know it's as good as it can get when I'm done.

Does yours run auto climate or manual?

EDIT: you know, I think it was pulling low 50's on the vent before it warmed up come to think of it. Strange that I get the same symptom even when the heater core is bypassed. I wonder if insulating that low pressure line on the psg fender would make a difference?

I'm auto climate.  And yeah, insulating the low side lines would probably help.  The rubber one to the receiver / dryer runs pretty close to the headers on mine, so I'm sure that doesn't help.  The dryer gets baked a bit too.  I should give that a try at some point.  

A/C being weaker at idle is normal due to lower compressor RPM.  Yours will be a bigger difference than mine, as you've got a mech fan (which moves less air at idle), while my fan is electric.  

Edit: Thinking about it, insulating the low side might help engine cooling slightly.  It'll reduce the amount of heat the condenser has to get rid of, reducing the temperature of the air going into the radiator.  

Well, my problem has self-corrected. My high side vapor line blew out. The static pressure was below a hundred, and the low side pressure was 35. The vent temp was 56°, as measured with my Longacre tire pyrometer stuck in the vent. Now I need to get a hose made, etc. 

I'm actually thinking about taking it to an AC guy, making sure it's squared away, and having it charged with R-12, just like Ford intended. 

Don't go the r12 route. Cost and availability on that are ridiculous last time I checked. You WILL have leaks eventually,  it's an old car, but you wont be able to touch it if it's got r12.

Honestly, I'm not sure the hard parts for an R12 system are available anymore.

Sucks that it blew the hose but at least now you've got an opportunity to sort it out correctly. 

I put the thermometer in the vent while driving around today. At every traffic light it went up to 75-80 degrees and while driving it would get down to 63-65 then go back up to 75ish, then down,  then up....That just screams low fill to me but I haven't put the gauges back on it.

snailmont5oh said:

Well, my problem has self-corrected. My high side vapor line blew out. The static pressure was below a hundred, and the low side pressure was 35. The vent temp was 56°, as measured with my Longacre tire pyrometer stuck in the vent. Now I need to get a hose made, etc. 

I'm actually thinking about taking it to an AC guy, making sure it's squared away, and having it charged with R-12, just like Ford intended. 

Redtek will go into an r12 system and work at the same pressures I believe. It’s available on Amazon. Mostly propane I think. 

A couple pounds of propane pressurized in a leakage-prone system in an enclosed space with a hot lump of metal running hundreds of spark driven gasoline explosions per second sounds like a great plan. No unintended consequences there.