Short cycling but not low on 134a

Edward Owner/Technician San Antonio, Texas Posted   Latest   Edited  
Question
HVAC
2003 Jeep Liberty Limited 3.7L 4-spd

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.....

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Christopher Technician
San Antonio, Texas
Christopher Default
   

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?

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Edward Owner/Technician
San Antonio, Texas
Edward Default
 

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

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David Owner/Technician
Red Springs, North Carolina
David Default
 

Make sure you have proper air flow through the condenser. What is your ambiaint temp?

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Edward Owner/Technician
San Antonio, Texas
Edward Default
 

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

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David Owner/Technician
Red Springs, North Carolina
David Default
 

The fans may operate, yet you can still have an airflow issue. Restricted condenser and or radiator.

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Edward Owner/Technician
San Antonio, Texas
Edward Default
 

Thanks David I will double check and isolate this before moving on

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Anthony Technical Support Specialist
Kirkwood, Pennsylvania
Anthony Default
 

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

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Edward Owner/Technician
San Antonio, Texas
Edward Default
 

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

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Ray Diagnostician
North York, Ontario
Ray Default
 

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.

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Edward Owner/Technician
San Antonio, Texas
Edward Default
 

Hi Ray I will double check to make sure 👍

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Paul Mechanic
Harvey, Illinois
Paul Default
 

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.

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Edward Owner/Technician
San Antonio, Texas
Edward Default
   

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

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Jim Curriculum Developer
Frederick, Maryland
Jim Default
 

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

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Edward Owner/Technician
San Antonio, Texas
Edward Default
 

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

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Jim Curriculum Developer
Frederick, Maryland
Jim Default
 

What Service information are you using and what are the performance test specification for the vehicle?

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Edward Owner/Technician
San Antonio, Texas
Edward Default
   

Hi Jim IAM using prodemand and identifix they don't state a spec.

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Jim Curriculum Developer
Frederick, Maryland
Jim Default
 

Identifix shows a spec under the Motor Specifications for A/C Refrigerant. It agrees with what I found in MotoLogic.

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Edward Owner/Technician
San Antonio, Texas
Edward Default
 

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 👊

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Paul Mechanic
Harvey, Illinois
Paul Default
 

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.

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Edward Owner/Technician
San Antonio, Texas
Edward Default
 

Hello Paul Interesting point so I would verify the cycling input signal or transducer signal....there a schematic posted

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Paul Mechanic
Harvey, Illinois
Paul Default
 

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

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Edward Owner/Technician
San Antonio, Texas
Edward Default
 

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

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Jim Curriculum Developer
Frederick, Maryland
Jim Default
 

Update?

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John Instructor
Beaver, Pennsylvania
John Default
 

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.

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Paul Mechanic
Harvey, Illinois
Paul Default
 

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.

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Jim Curriculum Developer
Frederick, Maryland
Jim Default
 

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.

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Edward Owner
San Antonio, Texas
Edward Default
 

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...

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