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A/C compressor short cycling

Tiny
RDANNENFELSER
  • MEMBER
  • 2001 FORD RANGER
  • 3.0L
  • V6
  • 2WD
  • AUTOMATIC
  • 195,007 MILES
A/C system pushing out only partially cold air and compressor is short cycling.

Compressor cycling clutch engagement/disengagement every one to two seconds and pressure at the low-pressure port bounces/fluctuates between 20–40 PSI.

A/C system was allowed to run after engine start up on the MAX cab air re-circulation setting for a minimum of three minutes prior to the pressure reading being taken. Ambient temperature was about 75° with high humidity.

Considering that the pressure at the low-pressure port bounces between 20–40 PSI, would the poor cooling/compressor cycling likely just be due to the system being low on refrigerant and in need of a charge or would it be a safe bet to expect there to be other part/electrical problems involved?

Really just would like to get an idea of if I'd be wasting my time/money buying a can of R134A and shooting it in there.

Thanks for any help/input you can provide.
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Monday, July 1st, 2019 AT 2:03 AM

11 Replies

Tiny
STEVE W.
  • MECHANIC
  • 13,473 POSTS
Welcome back to 2CarPros. Short cycling could be from a low charge, however you really need to check the high side pressure to be sure. A high side blockage could cause the same symptom. I would start with a gauge set, if you don't have one they are a "loaner tool" at many of the chain stores. For the high side you want to see around 2.3 times the ambient temperature if the pressure is correct. So say you have a 90 degree ambient temperature, the windows down, AC set to max and the engine turning about 1,000 rpm's. With the clutch engaged you would see a low side pressure around 30-40 psi and the high side would be around 210-220 psi. If you see a high side lower than that it's likely low on R134A, if however you see well above that (300 or more at that temperature) you likely have a blockage in the system.
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Monday, July 1st, 2019 AT 3:38 AM
Tiny
RDANNENFELSER
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I used a professional A/C gauge set tonight from O'Reilly Auto to test the high-pressure port. The high-pressure port PSI is fluctuating between 145-165 while the low-pressure port is still fluctuating between 20-40 PSI. Ambient temperature was roughly about 85 degrees at the time of the PSI readings.

85 x 2.3 = 195.5

Safe to conclude the system needs refrigerant despite whatever reason at whatever point caused the partial loss?
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Monday, July 1st, 2019 AT 8:41 PM
Tiny
STEVE W.
  • MECHANIC
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Yep, you have a low charge in the system. It's not uncommon for a system to leak a bit from the compressor seal over time. Being this is an 01 that is likely the issue. I would probably recover the charge in it, then pull a vacuum and see if it holds. If it holds add in some dye and recharge the system. That would also let you look for leaks at a later time if things got worse. Or just top it up with some R134A that has dye in it until you get good pressures and cold air and call it done.
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Monday, July 1st, 2019 AT 8:59 PM
Tiny
RDANNENFELSER
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Thanks, Steve. I appreciate the help.
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Monday, July 1st, 2019 AT 9:13 PM
Tiny
RDANNENFELSER
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I shot a can of refrigerant into the system. A/C now blows cold, but only temporarily for roughly five to fifteen minutes before the air turns warm. Shutting the A/C off temporarily and then turning it back on does make the air blow cold again. Any idea as to the likely cause of this?
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Thursday, July 4th, 2019 AT 11:18 PM
Tiny
STEVE W.
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What are the pressures running? It sounds like it's overcharged now.
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Friday, July 5th, 2019 AT 10:50 AM
Tiny
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Can't check the high pressure since the gauge I used before was a loaner tool from O'Reilly Auto, but when I went to check the low pressure I realized that the compressor is still short cycling at times. Gauge on the low-pressure port is showing a fluctuation roughly between 25-40 PSI when compressor is short cycling and a steady 25 PSI when not cycling.
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Friday, July 5th, 2019 AT 12:41 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,643 POSTS
It sounds like you are low on charge again so you could have a leak. here is a guide to help you check:

https://www.2carpros.com/articles/air-conditioner-leak-detection

Please run down this guide and report back.
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Friday, July 5th, 2019 AT 1:05 PM
Tiny
STEVE W.
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I would get a gauge set and check it again. You either have a leak or something is wrong in the system.
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Friday, July 5th, 2019 AT 3:17 PM
Tiny
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Was finally able to use an A/C manifold gauge set again to read the high pressure. What the gauges showed this time is definitely above my knowledge level in understanding what it indicates.

With the compressor cycling, the high pressure fluctuated approximately between 155-190 PSI while the low pressure fluctuated between 150-250 PSI in the retard area of the gauge. I've attached a short video of the gauges showing this.

Also, I checked the high and low pressures with the A/C manifold gauge set around 10:30 yesterday morning. Later on in the evening I decided to hook up just a basic Interdynamics gauge to read the low pressure just out of curiosity and the gauge showed a fluctuation between 25-40 PSI with the compressor cycling.
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Friday, July 12th, 2019 AT 8:40 AM
Tiny
KASEKENNY
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Just to offer some suggestions on this as this is a common issue when you either have an overcharged system or there is a restriction in the system. We need to start with evacuating the system and pulling it into a vacuum to find out if it will hold a vacuum. Then when we recharge it, we need to find out how much freon it takes. If it takes the proper amount and still does not operate correctly then the compressor is most likely faulty.

https://www.2carpros.com/articles/re-charge-an-air-conditioner-system

Take a look at the chart below. This shows that when your low side is high what the possible cause is. However your system is not relieving the pressure on the low side which tells me you most likely have a restriction in the system.

Prior to putting freon back in the system, use about 20 PSI of compressed air and blow through all the lines and components except the compressor just to find out if this will pass air through them.

Please let us know what you find with this.

Thanks
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Wednesday, August 4th, 2021 AT 5:32 PM

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