Model: Grand Cherokee Laredo
Engine Size: 4.7L
Refrigerant Type: r134a
Ambient Temp: 101
Pressure Low: 40
Pressure High: 225
Country of Origin: United States
2003 Grand Cherokee Laredo 40K Original Owner
Ambient Temp: 101ÃÂ°
Initial static pressure readings: L=115 H=110
Initial readings after starting and running at 5oorpm were L=55 H=2oo with a vent temp of 60ÃÂ°
Somewhat stable idle pressures at 500RPM were L=40-45 H=225-250
At 1500RPM Low pressure dropped to between 20-18 and high was 225. When the pressure dropped to 18, the compressor cycled off and pressure on the low side jumped to around 50. The fans came on and the pressure dropped on the low side to around 20 to 25.
I shut the system down and after 5 minutes the static pressures were both at 125
After the system was at rest for about 20-minutes I started to add some r134a. At 1500RPM the low side came up from 20 to 40. The high was stable around 250, but the vent temperature rose to over 80 and wouldn't come down. I shut off the r134a and turned the system off. Static pressures returned to around 125 on both low and high. After the vehicle sat for a while I restarted it and the vent temp came down to around 59ÃÂ°.
I have been having some problems with this system, sometimes its pumping out cool air (50ÃÂ°vent temp) and then it just stops cooling. The evaporator was replaced when the vehicle was about a year old and the system hasn't been checked since. Vehicle has 40K on it and I am the original owner.
I also bled the charge line before opening the low pressure side to charge.
At times the system acts like its just a low charge. Other times is acts like there is blockage somewhere, but there isn't any indication of this on the gauges. This system used to freeze you out (38ÃÂ° vent temp)but now it's just barely comfortable. This GC is also a Laredo and not a Limited so I don't think blend doors are an issue. I can turn the manual temperature control to hot when the a/c is on and it changes to hot air and back to cold when changed back to cold. The compressor shutting off when the low pressure side reached 18 seems normal and that's what I believe it should do with a low charge to protect the compressor. But what I don't get is why the air temp would increase when trying to do a charge?
Any thoughts? At his point I am about ready to evacuate the system and do a recharge, but don't want to have to turn around and start replacing additional parts.
Maybe someone has encountered this before?
Thanks in advance for any insight!
I tend to agree with you that the system was probably undercharged initially. When you added some R134 your low side pressures seem better than your 80 degree vent temps would indicate. Several explanations possible. Gauges inaccurate. Heater valve leaking hot water to heater core/airbox. I would probably evacuate and recharge with dye added so that you know were you are and can detect potential leaks.
Those pressures are awfully low for 101F, especially the low side. The compressor should not be cycling at that ambient unless the blower motor has come to a stop, or the interior of the vehicle is cold enough to hang meat.
I'm thinking you have a problem with your expansion valve. With the engine running a 2,000 RPM, the A/C on high blower, and all windows open, allow the system to stabilize and record your pressures. Now partially cover the condenser to obtain approximately 350 PSI on the high side (be careful). If the low side pressure also rises, the TXV is suspect.
You can also try alternately hitting the head of the TXV with extreme heat and cold (be careful). If the pressures do not change, or change very little, the TXV is probably.
Are the suction lines sweating excessively? If so, with those low humidity readings, that is likely an indication of a flooded evaporator - again TXV.
Thanks for the replies!
JJM: Hydraulic fans are working fine and coming on when they should. So that problem has been eliminated. Interior blower motor also working okay. I took a drive yesterday afternoon when the temperature was 111ÃÂ° outside. Air coming out of the a/c vents never dropped below 60 and most of the time was around 65-70. It seemed at higher engine RPM's the compressor would kick out. Couldn't really see and didn't have a gauge set connected so there is no way of knowing. There is never at any time any sweating of the suction lines.
I still find it odd that while trying to add r134 the vent temps would rise to above 80ÃÂ° and the low and high side pressures rose to where they should be with the high temps and low humidity. I am about ready to replace the TXV, evacuate and recharge.
I don't find it odd if the TXV weak. Refrigerant pressure overcomes the ability of the diaphragm to control superheat. Before tearing into the system, perform the quick simple tests as described for more confirmation. Hate to just throw parts a problem.
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