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Unread 01-13-2009, 09:19 PM   #1
mailforjon
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WJ: someone with A/C low/high side pressure expertise?

ive been having difficulty with the defrost lately (not defogging well) and assumed i had a bad heater core, broken recirc. door or something like that.

i bought a nice set of A/C manifold gauges and hooked them up with the blower on full blast, and the A/C and RECIRC buttons on. ambient temp. was 30F.

readings start:

LOW: 20psi
HIGH: 100psi

simultaneously and slowly (over 15 seconds or so)
LOW: increases to 35psi
HIGH: decreases to 50psi.

then, the compressor clicks (on/off?) and:
LOW: decreases slowly back to 20psi (creates a vacuum?)
HIGH: side slowly increases back to 100psi.



can anyone with experience with A/C pressures diagnose what is going on?

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Unread 01-13-2009, 09:41 PM   #2
sadass
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a little info for you, sounds low!
This is a complicated thing. The high pressure side will measure in excess of 250 psi, but that's not important. When filling 134a, you only need to watch the low pressure side.

When the compressor kicks on (which it will only do when the pressure is above 40 psi) the pressure will drop. If the lines are full enough, the pressure will remain around 40-45 psi while it's running. When the compressor kicks off, the pressure will rise to 90-100 psi., as the high and low pressure sides even out in the expansion tank.

If your lines aren't full enough, the compressor will either not kick on at all, or it will kick on for a second, and the pressure will drop to 20 psi or less, and it will kick off. If the lines are empty enough, it will do this on and off, on and off, pretty frequently, like every 5 seconds or less.

Be sure to hold the cans up-side-down and high in the air as you release them into the system. Otherwise, they will release much slower, as you will be releasing only what gas has expanded. NEVER connect the cans to the high pressure side. They will explode in your hand, not only removing your hand and eyes, but will also freeze your skin instantly.

Just keep applying cans until the pressure remains at 40-45, depending on your vehicle(it will find this pressure on it's own. you will see it remain there and not drop past a point. if it has not found it's point, it will never stop dropping till the compressor kicks off.) Do this a little at a time, stopping to watch the pressures.

Once you reach this steady pressure reading, finish off the can, and you can probably add another can or just a half a can. You don't want to add too much, or else the pressure will build up too much on the low side. If this happens, (and only if you have 134a) you can release the excess pressure from the valve just like you would emptying a tire. Be sure you do this on the LOW side, and do it while the vehicle is running, so you can watch the pressure. Be careful, and wear leather gloves if you have to remove some, because what comes out will freeze your skin.
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Unread 01-13-2009, 10:17 PM   #3
Spankee
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expansion valve could be faulty if your refridgerant level is good.
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Unread 01-14-2009, 04:52 PM   #4
mailforjon
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does it matter that it was 30F when i did this pressure test?
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Unread 01-14-2009, 05:25 PM   #5
spenc
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when the compressor is idle the pressures will "equalize" at 30 deg outside temp you would expect to see around 25 psi with nothing running, if idle long enough they shoud be the same, only when the compressor is running, will you get the pressure differential that it needs to cool, at such low ambient temps, it is normal for the compressor to run and kick off, this keeeps the evaporator from icing up, be carefull adding too much when it is this cold outside,when it gets hot you could flood the compressor and ruin it

Last edited by spenc; 01-14-2009 at 05:35 PM.. Reason: more info
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Unread 01-14-2009, 06:22 PM   #6
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ussally u check the Level when it's warm dont u? got somebody with a heated garage?

yea if the Regfridge or PUREON now called isnt warmed up the compressor gets a big nasty shot of chunky fluid.
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Unread 01-14-2009, 06:31 PM   #7
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All refrigerant cans have the warning to dispense in upright position only. Reasoning for this is you don't want the compresser to get hit by a slug of liquid and hydrolock.....vapor only, it takes time......

Klaus Cook
Houston, Texas
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Unread 01-14-2009, 06:39 PM   #8
xJoshxx
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Quote:
Originally Posted by CaseyC View Post
All refrigerant cans have the warning to dispense in upright position only. Reasoning for this is you don't want the compresser to get hit by a slug of liquid and hydrolock.....vapor only, it takes time......

Klaus Cook
Houston, Texas
WHICH IS WHY U WAIT FOR UR JEEP TO WARM UP BEFORE BLASTING THE DEFROST!
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Unread 01-14-2009, 08:27 PM   #9
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Quote:
Originally Posted by CaseyC View Post
All refrigerant cans have the warning to dispense in upright position only. Reasoning for this is you don't want the compresser to get hit by a slug of liquid and hydrolock.....vapor only, it takes time......

Klaus Cook
Houston, Texas

agreed, right side up is probably better. Besides, when it is up side down, the top of the can is still filling with vapor at the same pressure as the liquid. it will only fill the ac system until the can and low pressure port are at the same pressure, and this pressure will be the same not matter the position of the can. I would rather take a bit longer than risk killing the AC system
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I am not one to be changing lanes at 70 mph on a lifted truck on 33's, but since I am in Miami, I have to be prepared for the continuous influx of new drivers whose previous ride was a bicycle with wooden wheels.
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badger, badger, badger, badger, badger, badger, badger, badger, badger, badger, badger, Mushroom!!! :D
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Unread 01-14-2009, 08:28 PM   #10
elmer_fud
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also, I would check the heater core and doors before worrying about the AC to much. Vehicles without AC still have defrost and it works fine once the engine starts to warm up.
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Quote:
Originally Posted by Speedycat View Post
I am not one to be changing lanes at 70 mph on a lifted truck on 33's, but since I am in Miami, I have to be prepared for the continuous influx of new drivers whose previous ride was a bicycle with wooden wheels.
Quote:
Originally Posted by FPKites View Post
badger, badger, badger, badger, badger, badger, badger, badger, badger, badger, badger, Mushroom!!! :D
Quote:
Originally Posted by ZeeJay1997 View Post
Or just tie a 12 lb fish to a one foot pipe.
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Unread 01-15-2009, 10:23 AM   #11
mailforjon
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Quote:
Originally Posted by elmer_fud View Post
also, I would check the heater core and doors before worrying about the AC to much. Vehicles without AC still have defrost and it works fine once the engine starts to warm up.
i thought you needed a functional A/C system to have an effective defrost?

dont you need a working evap to pull the moisture out of the air?
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Unread 01-15-2009, 02:57 PM   #12
elmer_fud
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Quote:
Originally Posted by mailforjon View Post
i thought you needed a functional A/C system to have an effective defrost?

dont you need a working evap to pull the moisture out of the air?
no, you do not need a functioning AC.

As air warms up it can contain more water. The defrost heats the air so it can pick up water off the windshield.

The AC makes the defrost more effective for the first few minutes it is on, but after that it doesn't do much. The defrost blows hot air on the windshield to heat it up a bit and dry off any moisture. Hot air can store more water than cold air, so this is why defrost heats up the air.

The AC makes the defrost more effective when the engine is cold because it cools the air first making the water seperate from the air.

My ZJ doesn't have working AC ( I disconnected it) and the defrost still works fine once the engine starts to warm up slightly. this is because the heat from the engine is transferred to the air. The heat makes the air dryer and removes moisture from the windshield.

does this make since? I am not sure how well I explained it.
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Quote:
Originally Posted by Speedycat View Post
I am not one to be changing lanes at 70 mph on a lifted truck on 33's, but since I am in Miami, I have to be prepared for the continuous influx of new drivers whose previous ride was a bicycle with wooden wheels.
Quote:
Originally Posted by FPKites View Post
badger, badger, badger, badger, badger, badger, badger, badger, badger, badger, badger, Mushroom!!! :D
Quote:
Originally Posted by ZeeJay1997 View Post
Or just tie a 12 lb fish to a one foot pipe.
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Unread 01-15-2009, 04:01 PM   #13
spenc
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the most important question I can think of is: did the a/c work last summer, if so DON"T mess with it!!!
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Unread 06-20-2015, 05:45 PM   #14
Andrewc135
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So, what should be my step from here on
Clearly i want to release pressure
but from there on?
From what i see the clutch doesn't engage at all...
Had my head gasket redone about 3k miles and 2 months ago...
img_8779-1-.jpg  

Last edited by Andrewc135; 06-20-2015 at 06:14 PM..
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Unread 06-21-2015, 07:36 PM   #15
Oldfrog
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BTW, this is a 2009 zombie thread.
You need to engage the clutch to get a reading. Do this by jumping the high pressure switch.
The low side will go down when the clutch engages. My guess is that it's low on r134. Add some and the clutch will engage without jumping the connector.
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