Short cycling but not low on 134a
Hello guys working on a Jeep Liberty Limited 3.7L that short cycling but its not low on Freon. The compressor,dryer, low pressure switch,and orifice has been replace they are all aftermarket parts. When i hook up my gauges my static pressures 86 low side and 84 high side, Vehicle running low side at 38 psi and 150 psi high side, then it starts short cycling so performed a evacuation and recharge with 1.37lbs of freon recheck pressures same issue short cycling, so i check the cycling switch removed it for inspection didn't fine any issues i believe the switch is a normally open and the pressure will close it. So i decided to bypass the cycling switch to check if my compressor would stay on and what kind of pressure i would get. I notice the low side went down to vacuum and high side around 175 psi in the 5 sec running..... Maybe i have a restriction some were in my evaporator or dryer also notice the cycling switch is mounted right on top of the dryer.....
Assuming you have good airflow through the evap, it does sound like a low-side restriction. Have you checked the txv or orifice tube (not sure which is equipped) for clogs and/or proper operation? Do you have a FLIR you can use to check the lines for an unexpected temp change?
Hello Chris I checked the orifice tube which is permanently installed in the liquid line side. I the line was replaced with a four seasons line. But I will recheck for temp change arcoss the line thanks for the input
Make sure you have proper air flow through the condenser. What is your ambiaint temp?
Hello David Yes I was thinking that I might not have proper airflow but the fan cames on and goes full operation if my high side goes up. My Ambiaint is around 81
The fans may operate, yet you can still have an airflow issue. Restricted condenser and or radiator.
Thanks David I will double check and isolate this before moving on
Hi Edward: If you want to be lazy and prove effective fan operation, spray a garden hose on the condenser while watching your pressure readings. BTW, is this one of those condensers which can be installed upside down by mistake? HTH, Guido
Hey Anthony I have not try that on this vehicle like David said I need to isolate this before moving on. The condenser has been replaced with a aftermarket unit it can only be installed one way.... thanks for the input
Your weight scale might not be accurate. Add half a pound of R134A to see if the high side pressure goes up and the cycling should slow down if the system was undercharged.
Hi Ray I will double check to make sure 👍
Are you seeing the compressor cycle off at 38 psi? Is the switch controlling clutch or pcm looking at pressure? Have you connected a scanner to monitor whatever modules maybe involved in ac operation? You may have a faulty switch/sensor as well as a suspect compressor given you can lower pressure into negative territory, but your high side doesn't reflect the appropriate increase.
Hello Paul Looks like the switch is PCM control as a input for the clutch to engage. Let me ask you when I bypass the switch the low side went to vacuum in about 5secs I feel like there's restriction between the accumulator and evaporator...but I need to be sure in my diagnosis
What were you trying to fix? Original Complaint? What are the results of the A/C performance test as outlined by the manufacturer? How was the system charged and with what equipment? Does the equipment use charge compensation or hose compensation or both? Which one was used? What service information system? Any TSBs? My SI shows 1.63 pounds for the vehicle you specified so your charge of 1.37
Hello jim That's interesting the 1.37 lbs is right off the label on the vehicle could you confirm that's correct 1.63 pounds that would confirm why IAM chasing my tail...1J4GL48KX3W674722
What Service information are you using and what are the performance test specification for the vehicle?
Hi Jim IAM using prodemand and identifix they don't state a spec.
Identifix shows a spec under the Motor Specifications for A/C Refrigerant. It agrees with what I found in MotoLogic.
Wow Jim I will confirm if this fixes the issue being the last shop and I also went off the tag on the vehicle. Thanks for the help brother 👊
If it's pcm controlled, you need to view the data pid for the pressure, it may be lower then you gauge reports. While I agree going off of level affixed to vehicle, you may want to check another source. Regardless of amount of charge, you have to confirm the pcm pid agrees with gauge.
Hello Paul Interesting point so I would verify the cycling input signal or transducer signal....there a schematic posted
Unfortunately, the schematic is not displaying correctly on my phone, but I did see the the low side opens up at 25 psi and resets at 43. Perhaps your gauges are suspect. One of your measuring devices may be incorrect. You need to verify all before you continue with diagnosing system performance and possibly wasting time replacing parts. If you are low on charge, the gauge readings may be
Paul I was informed that 1.37lbs is not correct charge will be revising that to 1.63lbs and checking pressure at this baseline. Will post on what I fine...thanks again
Did you try to measure the surface temperature of the components to see if you can locate a restriction? There should be a temperature change right after a pressure change.
I find it a bit weird that he was all over this on Easter Sunday, but can't seem to get a response during the work week, unless his choice of worship practice prevents him from testing/responding at this time.
I was really hoping to hear a resolution on this as well. Otherwise it is not an opportunity for others to learn anything from the exercise. The fact that it has been left hanging for weeks is disappointing.
Hello Jim Sorry for the delay, the customer is driving the vehicle at this time I was hoping to resolve this issue quickly unfortunately they will be bringing back there vehicle in a few weeks. I will do my best to the complete this case study...