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A/C low/high side equal pressures

Tiny
RDANNENFELSER
  • MEMBER
  • 2001 FORD RANGER
  • 3.0L
  • V6
  • 2WD
  • AUTOMATIC
  • 208,785 MILES
On an orifice tube air conditioning system that is not cooling and has rapid compressor cycling part of the time, what would roughly equal pressure readings of about 105–110 PSI on both the low and high sides indicate? These PSI pressures are when the compressor is not cycling and the clutch not engaged.

Attached is a short video showing the pressures on a manifold gauge set of just before and then when the compressor begins cycling.
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Saturday, July 25th, 2020 AT 4:07 PM

19 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Great video. That really helps. There are a number of reasons that a compressor will short cycle. The top two are it is low on Freon due to a leak or the evaporator is frozen.

However, equal pressures are showing you that the compressor is not operating. This may be due to the compressor if the prior two reasons are not the issue. If the compressor were no short cycling then we could just assume that it is not running due to no power however, we know that is not the issue so we can rule that side of the system out completely.

That leaves low on Freon due to a leak so we need to pull it down into a vacuum and make sure it holds a vacuum for about an hour. If it does, charge it properly and retest the system.

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

If that does not fix the issue, check the evaporator for freezing after you have it properly charged because low Freon could cause it to freeze as well. So that means we need to properly charge it to ensure low Freon is not the issue.

Here is a chart that will help figure out possible pressure issues. Let me know what you find with this and we can go from there. Thanks
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Saturday, July 25th, 2020 AT 4:56 PM
Tiny
ASEMASTER6371
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  • 52,797 POSTS
Good evening,

Is the compressor clutch engaged with those readings?

https://www.2carpros.com/articles/car-air-conditioner-not-working-or-is-weak

If they are, you need to replace the compressor, dryer and the orifice tube.

https://www.2carpros.com/articles/replace-air-conditioner-compressor

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

If it is not then we need to find out why.

I attached a wiring diagram for you to view. Do you have a test light for some testing.

https://www.2carpros.com/articles/how-to-check-wiring

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Roy

REMOVAL

CAUTION: When installing a new A/C compressor due to an internal failure of the old unit, you must carry out the following procedures to remove contamination from the air conditioning system:
If A/C flushing equipment is available, carry out flushing of the air conditioning system.
If A/C flushing equipment is not available, carry out filtering of the air conditioning system.
Install a new evaporator core orifice.
Install a new suction accumulator.

NOTE: Replacement of the suction accumulator is not required when repairing the air conditioning system except when there is physical evidence of system contamination from a failed A/C compressor or damage to the suction accumulator.

1. Perform the Refrigerant Discharging and Recovery Procedure.

imageOpen In New TabZoom/Print

2. Position the air cleaner outlet tube aside.
1 Loosen the clamp.
2 Disconnect the crankcase ventilation tube.
3 Position the air cleaner outlet tube aside.
3. Remove the accessory drive belt from the A/C compressor pulley.

imageOpen In New TabZoom/Print

4. Disconnect the electrical connector.

imageOpen In New TabZoom/Print

5. Remove the clamp nut on the compressor manifold and tube assembly.

imageOpen In New TabZoom/Print

6. Loosen the bolt and disconnect the compressor manifold and tube assembly from the A/C compressor.

imageOpen In New TabZoom/Print

7. Remove the bolts and the A/C compressor.
Discard the O-ring seals.

INSTALLATION
1. To install, reverse the removal procedure.
If a new A/C compressor is to be installed, the A/C compressor clutch field coil and the A/C clutch plate must be transferred from the old unit.
Lubricate the refrigerant system with the correct amount of clean PAG oil or equivalent. See: Refrigerant Oil Addition.
Install new O-ring seals lubricated in clean PAG oil or equivalent.
2. Evacuate, leak test, and charge the refrigerant system.
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Saturday, July 25th, 2020 AT 5:06 PM
Tiny
BMDOUBLE
  • MECHANIC
  • 1,139 POSTS
Low on Freon, check the front of the compressor for leaks, these trucks are bad about it.
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Monday, July 27th, 2020 AT 8:29 AM
Tiny
RDANNENFELSER
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  • 43 POSTS
Those equal, steady pressure readings of 105-110 PSI on both the high and low sides are with the compressor clutch not engaged. The clutch only engages during compressor cycling and while cycling the low side pressure drops and the high side increases.

As for electrical testing tools, I do own a test light and can either borrow or purchase a multi-meter.

And as for leak testing, I have a a single application 1.7 ounce aerosol can of UV leak dye. If I were to use this dye, would the A/C system need flushed afterwards before recharging?
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Monday, July 27th, 2020 AT 8:36 PM
Tiny
ASEMASTER6371
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  • 52,797 POSTS
Okay, I need the readings for when the compressor engages. I need to see how low the low side is and how high the high side is.

They are supposed to change when the compressor comes on line.

Roy
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Tuesday, July 28th, 2020 AT 2:54 AM
Tiny
RDANNENFELSER
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  • 43 POSTS
The low side pressure drops and fluctuates consistently between 20 and 40 psi during compressor cycling.

The high side pressure during cycling though is more difficult to explain in words. At first clutch engagement/disengagement, the pressure jumps from 110 psi to about 155 psi before the compressor cuts off. Cycling continues for about 8 minutes and as it does the overall pressure on the high side increases gradually until reaching about 215 psi. Pressure then begins to gradually decrease until dropping back to a steady 100 psi when cycling stops.

Like I said, the high side pressure is difficult to explain. The attached video shows the pressures over the entire cycling duration and even just skipping through it should provide better information than what I can give in words.
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Sunday, August 2nd, 2020 AT 1:37 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Based on that video, you need an expansion valve. The compressor is cycling because the low pressure goes below 20 pounds and the low pressure switch open at 20 pounds.

You have an orfice tube. I attached a picture of the tube and the tools required to change it.

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

Roy
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Sunday, August 2nd, 2020 AT 5:28 AM
Tiny
RDANNENFELSER
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Thank you. After changing out the orifice tube, should the accumulator be replaced and is there a need to flush the system before evacuating/charging?
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Sunday, August 2nd, 2020 AT 10:06 AM
Tiny
ASEMASTER6371
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Yes, anytime you open the system, the dryer should be replaced.

No, to the flush. Just make sure you evacuate it for about 1 hour.

Roy
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Sunday, August 2nd, 2020 AT 10:14 AM
Tiny
RDANNENFELSER
  • MEMBER
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As for the orifice tube replacement, RockAuto and O'Reilly list both fixed and auto adjusting. I assume I will need just a fixed, correct?
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Monday, August 3rd, 2020 AT 1:25 PM
Tiny
ASEMASTER6371
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That is correct.

The rock auto is the correct one.

Roy
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Monday, August 3rd, 2020 AT 1:28 PM
Tiny
RDANNENFELSER
  • MEMBER
  • 43 POSTS
One last question. After replacing the orifice tube and accumulator, for recharging the system after pulling a vacuum, does PAG oil need to be added or should just using refill cans of R-134A alone be sufficient? Also, should the cans of refrigerant I use be the type that already include lubricant or should I just use cans containing R-134A only with no additives?
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Friday, August 7th, 2020 AT 5:16 PM
Tiny
ASEMASTER6371
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You need to add 2 ounces of pag oil to the freon system before charging.

No, just use the R134 freon for charging. No additives.

Roy
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Friday, August 7th, 2020 AT 5:28 PM
Tiny
RDANNENFELSER
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  • 43 POSTS
I replaced the orifice tube, pulled a vacuum on the system which did hold, and recharged the system with the specified 30 ounces of refrigerant.

Initially, the system seemed to be operating normally again. The low and high pressures were in normal ranges, compressor clutch cycling ceased, and cold air was blowing from the vents again.

After about 15 to 20 minutes though of the system running after recharging, I heard a noise that caught my ear that I can't really explain in words. The low pressure had increased while the high pressure fell. I noticed an excessive amount of condensation on the accumulator lines as well as some condensation in the cab on the windows and on the thermometer I had placed in one of the vents. There was also a large amount of water that had drained on the floor beneath the vehicle from under the evaporator core housing. The air from the vents was not as cold as before and by the following day not cold at all. The compressor clutch has also began to cycle again.

Based upon all the details, what likely happened to cause the system to be operating normally at first blowing cold air and then shortly later experience a low pressure spike/high pressure fall, discharge an excessive amount of water, and seemingly lose its refrigerant charge?
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Saturday, August 22nd, 2020 AT 11:40 AM
Tiny
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Okay, what are the pressures while it was running after the noise?

Roy
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Saturday, August 22nd, 2020 AT 5:39 PM
Tiny
RDANNENFELSER
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I'm not certain and wish I had paid closer attention to exactly what the pressures were, but trying to remember from a glance I believe the low side was around 70 psi and the high side around 100 psi. As of today though when I hooked up the manifold gauge set again I read zero pressure on both the low and high sides. I'm also not able to drawn A/C vacuum at.
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Sunday, August 23rd, 2020 AT 3:25 AM
Tiny
ASEMASTER6371
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You have a leak, a big one from the sounds of it if you have no pressure and cannot pull a vacuum.

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

Roy
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Sunday, August 23rd, 2020 AT 3:41 AM
Tiny
RDANNENFELSER
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That's what I figured. Despite that the system was working properly at first with the pressures in normal ranges, do you think it was likely the evaporator itself or a connected line that blew a leak due to the evaporator being too clogged/freezing considering the excessive amount of water that discharged from beneath its housing?
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Sunday, August 23rd, 2020 AT 2:11 PM
Tiny
ASEMASTER6371
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You are going to have to inspect each line for the leak. More likely the condenser or the lines.

Roy
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Sunday, August 23rd, 2020 AT 2:21 PM

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