Low side or high side A/C charge port

Tiny
EDSEXTON81
  • MEMBER
  • 2010 CHEVROLET MALIBU
  • 2.4L
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 75,000 MILES
I am trying to add a small can of r134a Freon to our car. In the picture which port is high side and which one is low side? Any help is appreciated. Thanks!
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Friday, July 11th, 2014 AT 5:08 PM

6 Replies

Tiny
CARADIODOC
  • EXPERT
I am at an old car show and the wireless internet is not working very well. The photo did not show up. Regardless, the low-side port is on the compressor or the line coming to it from the firewall.

Be aware that refrigerant can cause frostbite and blindness. Professionals wear gloves, safety glasses, and a face shield. The ports are different, so if you get the wrong one, the fitting on the hose will not fit.

You should not be low on charge with such a new vehicle. There is no way to know how much refrigerant is in the system now without recovering all of it, then adding a measured amount. Too much overcharge can allow liquid refrigerant to slosh into the compressor and lock it up or damage it. That also moves where it changes from a liquid to a vapor. Where that happens is where it becomes cold, and you want that to be in the evaporator in the dash, not in the hose under the hood going to the compressor.
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Friday, July 11th, 2014 AT 7:47 PM
Tiny
EDSEXTON81
  • MEMBER
Thank you for your response Caradiodoc! I am re-posting the picture just to make sure I have the right ports. If I am correct the bottom port is the low side and the top port is the high side. Is that correct?
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Saturday, July 12th, 2014 AT 5:18 AM
Tiny
CARADIODOC
  • EXPERT
That appears to be right. The top pipe that winds around the strut tower should be coming from the condenser in front of the radiator. That would be the high side. The lower fitting should be on the pipe going to the compressor.

Be sure to reinstall the black plastic caps on the ports when you are done. Those valves will leak. Their job is only to hold the refrigerant in while you're putting the caps on. The caps have the o-ring seals that stop any leaking.
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Saturday, July 12th, 2014 AT 8:30 PM
Tiny
EDSEXTON81
  • MEMBER
Thank you so much for your help. I just needed to make sure I was going to use the right port. I have recharged several of my own vehicles and can usually gauge or determine what the issue is but in this case I am not so sure. My wife's car went from one day having great cold air to practically hot the next day. I got a small can and used the low side port without a pressure gauge so I did not know how much to use. So after like two minutes of rotated the can. The compressor kicked in but it makes a kind of weird noise or I will call it a rotation. I can plainly see the clutch engages but it almost immediately kicks back off and it keeps doing this over and over and every time it does it is pulling a lot of electrical power. I am assuming from when the clutch engages. The lights in the car dim more than they have usually in any other vehicle I have had. So anyways, I bought a gauge yesterday at Advance and the gauge while car is running and air fully on reads like 180 or so. It was in the red part. Have any ideas or is that normal? Would that go down if I start to try to fill it?
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Sunday, July 13th, 2014 AT 4:52 AM
Tiny
EDSEXTON81
  • MEMBER
90 psi not 180 sorry. Lol!
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Sunday, July 13th, 2014 AT 7:44 AM
Tiny
CARADIODOC
  • EXPERT
90 psi on the high side is low and indicates low charge, but I am not good at judging performance based on gauge readings. The problem is the low and high side gauge readings will stay fairly constant from a half pound under-charge to a half pound over-charge. The system is filled partially with liquid and partially with vapor. Adding more refrigerant just changes the locations of where it changes between the two states.

Also, the pressure of refrigerant under pressure with the system at rest will be very close to the air temperature around it. If it is seventy degrees in your garage, you are likely to find close to 70 psi on both gauges. If you were to release one pound to the atmosphere, some of what remains in the system would turn to vapor and expand, and the pressure would go right back to where it was. No matter how much you bleed off, the remaining liquid will keep expanding and vaporizing, and the pressure will stay the same, until it is fully vaporized and there is no liquid left.

I prefer to use a thermometer to verify the system is has the correct charge, (after I have added the measured amount). The pressure is regulated to not go much below 40 psi in the evaporator because that equates to about forty degrees. Any colder and you risk getting below thirty degrees at which point the condensation would freeze into a solid block of ice that would block air flow. The goal of the AC system is to only lower the air temperature about twenty degrees. It is the removal of the humidity that creates the comfort. Lets face it; sixty degrees is not comfortable when you are sitting still for long periods.
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Sunday, July 13th, 2014 AT 10:50 PM

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