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A/C compressor/low pressure switch location needed

Tiny
2HS
  • MEMBER
  • 2015 SUBARU FORESTER
  • 2.5L
  • 4 CYL
  • 4WD
  • AUTOMATIC
  • 74,000 MILES
Hello,

Newbie and first time posting. Hoping to get some help with A/C issue.

Vehicle listed above is a Limited.

Does anyone know where the A/C Low pressure switch is located on this car or if there's even one? I found the high pressure switch but don't see the low pressure switch. I've removed all the A/C lines and flushed the evap and lines but there is no low pressure switch to be found. Replaced condenser (due to a visible evidence of major leak) with Spectra Premium 7-4302 from AutoZone as well as the TXV. Drained compressor oil (not even close to 2.7 Oz that it calls for) and filled with 4 Oz of PAG 100 oil. Pulled vacuum and holds - confirmed no leak.

Trying to fix initial A/C issue where it blows warm air. The passenger side vents does get a little bit cool (60-70 degrees with ambient 85+) but the driver side vents stays warm. It does get a little cool after when car is moving/driving. But it never cools down to typical 35-40 degrees at the vents.

As I stated above, I've replaced the condenser, TXV, and flushed the evap core and lines. Vacuumed and Recharged but same issue. I am down to replacing the compressor as the last logical culprit and looking for some feedback from the group.

Some detail from troubleshooting:
- Ambient temp 85
- Static pressure is similar to outside temp on both Low & High side
- At idle, pressure readings: Low - 60psi / High - 275 with only about 12 Oz charge of refrigerant (total calls for 16-18 Oz). Compressor clutch does engage and stays engaged at all the times - never cycles. Both Low/High pressures continue to increase as more refrigerant is added so I stopped at 12 Oz. I believe the compressor may be weak and is unable to perform proper suction and compression. Can anyone concur?

Before I replace the compressor (looking to get a used unit from eBay), I want to confirm pressure switches are good and also check if anyone can concur that compressor is bad.

Also, does anyone have test procedure to properly check/test the switches?

Any help is greatly appreciated.

Thanks
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Saturday, July 11th, 2020 AT 1:50 PM

16 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,867 POSTS
Hi,

I have a question. I read through your post and noted that both high and low side pressure seem good. The are slightly higher than what I would expect at the ambient temp, but by no means indicate a bad compressor. It could actually be slightly over charged. At 85° F, pressure should be:

Low side - 45psi - 55psi

High side - 225psi - 250psi

Are you sure it has nothing to do with the blend door actuator in the vehicle. Here is what I suggest. Remove one of the actuators and see if it is working. If it isn't, that could be the entire problem. It sounds like the system is working properly but the cold air isn't getting into the vehicle.

Let me know.

Joe
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Saturday, July 11th, 2020 AT 7:03 PM
Tiny
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Hi Joe,

Good evening and thanks for responding.

The pressures you listed, I assume those are at idle and not revving at 2000 - 2500 rpm, correct? As I've stated, I've only charged 12 Oz of refrigerant (min 16 Oz and max 18 Oz on the sticker) and it already at the 60 / 275 psi and I figured it was getting too high so I stopped. How can that be an indication of over charged already when it is short of 4-6 Oz of the spec? All the info I've found and videos of auto A/C troubleshooting indicate pressures typically should be at Low: 35 / High: 175. Some also say High 250 psi is like the "red" zone. Hence, I am very concerned with my pressure readings. Is there a fail-safe way to test the compressor? The compressor is the last mechanical device in the A/C system that I've not replaced and I figured that would be the logical explanation for the high pressure readings.

I will check into the blend actuators as you suggested. Do you have any instruction/diagram/video on getting access to the blend door actuator? By the way, I assume this is different from the air flow directional vent control (top, bottom, top and bottom, defrost, etc.), Correct? The directional air flow all seem to work properly.

Also, do you know if there is a low pressure switch on this car and how to check/test these low/high pressure switches?

Thanks again.

-2Hs
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Saturday, July 11th, 2020 AT 7:55 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,867 POSTS
Hi,

The pressures are with the compressor engaged and at idle. As far as the pressure, understand that they are affected by ambient temperatures. The 35 / 175 would be typical at an ambient temp of around 75° F give or take. If Ambient temps reach 100°F or above, it isn't uncommon for the high pressure to reach over 300 psi.

If the compressor was the issue, you would not see that variation in pressure.

Here is a rule of thumb I always follow:

If the low side is low and the high side is high, there is likely a blockage such as an orifice tube or H block.

If the If the low side is high and the high side is low, then I would suspect a possible compressor.

If both are low, then add Freon

If both are high, normally it is over charged.

__________________________

If you look at pic 1, it is straight from the manual if both are high.

Next, the pressures switch on this vehicle is referred to as a triple pressure switch. It controls high, medium, and low pressure.

Here is the test procedures for checking it. The attached pics correlate with the directions.
_______________________________________________________
Pressure Switch (Triple Pressure Switch) - Inspection
Vehicle Sensors and Switches Sensors and Switches - HVAC Refrigerant Pressure Sensor / Switch Testing and Inspection Component Tests and General Diagnostics Pressure Switch (Triple Pressure Switch) - Inspection
PRESSURE SWITCH (TRIPLE PRESSURE SWITCH) - INSPECTION
INSPECTION
1. Connect the manifold gauge to the service valve on the high-pressure side.

2. Disconnect the connector.

3. Start the air conditioner, and check the operating pressure of switch by turning the compressor assembly (magnet clutch) to ON/OFF. Operation of each switch is as follows.

See pic 2

See pic 3

Note:
High pressure switch turns the compressor assembly (magnet clutch) to OFF when the refrigerant pressure becomes extremely high to prevent the evaporator, air conditioner piping and expansion valve from getting damaged or frozen, etc.

The middle pressure switch is used to effectively control the radiator fan output by judging high load/low load in normal pressure range.

The low pressure switch detects a refrigerant shortage and deactivates the compressor assembly (magnet clutch) if the refrigerant pressure is abnormally low. (Because any further compressor assembly operation in such a state may lead to compressor seizure)

____________________________

The last pic I attached shows the location of the pressure switch.

Let me know if this helps.

Joe
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Saturday, July 11th, 2020 AT 8:26 PM
Tiny
2HS
  • MEMBER
  • 8 POSTS
Hi,

Thank you for the info on the switch and diagrams/pictures.

Based on my troubleshooting thus far, I think I can automatically rule out the following:

1) Blockage: I've removed lines and did a flush. Replaced Condenser and Expansion Valve. So blockage is not the issue.
2) Low side is low.
3) High side is low.
3) Both are low.

Therefore, it leaves 2 possible options, either:
1) Both are high -or-
2) Both are within acceptable pressure.

So, based on these 2 options, would you concur and which would you think is likely accurate per pressure readings that I've provided? What would be the logical next step to continue troubleshooting the AC issue? I will still look into the blend door actuator.

Regarding rule of thumb, at ambient temperature 75 F, what pressure is consider:
- Low is low if reading is ___ psi.
- Low is high if reading is ___ psi.
- High is low if reading is ___ psi
- High is high if reading is ___ psi

Lastly, is there an absolute critical point for Low and High side pressures?

Thanks again.

-2Hs
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Saturday, July 11th, 2020 AT 9:13 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

At 75° F

Low pressure should be around 35 to 40.

High pressure should be around 150 to 170.

If the PSI is a few pounds either way, it is fine.

As far as the compressor, I feel it is fine. It may be over charged. I would check the blend doors and see if they are working.

Also, since the compressor is working, you should be getting cold air in the vehicle. That is why I am suspecting the door issue. Plus, you said one side is slightly cooler than the other.

As far as a critical point, it is all based on ambient temp. If pressure (regardless of temp) drops below approximately 25 psi, it's likely that the system will be inoperative. Under extreme heat (100°F and above), high pressure can reach up to 340 psi.

Let me know if I can help.

Joe
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Saturday, July 11th, 2020 AT 9:43 PM
Tiny
2HS
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Hi Joe,

I will check the blend doors. Yes, passenger side is cooler than the driver side.

I am baffled as to how the system could be over charged when I've only put in 12 Oz of refrigerant and the spec calls for minimum 16 Oz and max 18 Oz. I stopped at 12 Oz believing my pressures were getting too high.

Thanks,

-2Hs
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Saturday, July 11th, 2020 AT 10:03 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,867 POSTS
Hi,

Anything is possible. I understand your concerns regarding the amount of refrigerant you installed. It makes no sense to me as well.

Listen, if the blend doors are working properly, I will get in touch with the owner of the site. He lives in Southern CA, so he has done a lot with A/C. Perhaps I'm missing something he will pic up on.

Let me know.

Take care,
Joe
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Sunday, July 12th, 2020 AT 8:42 PM
Tiny
2HS
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Appreciate it Joe. I will not be able to get to work on the car again until the coming weekend, would you mind running the issue by the owner anyway? Just to get another opinion before I dismantle the dash console.

Thanks,

-2Hs
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Sunday, July 12th, 2020 AT 11:15 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,867 POSTS
Absolutely, I can do that. His name is Ken and he knows a lot related to A/C. Lets see what he says.

Joe
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Monday, July 13th, 2020 AT 6:45 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 48,289 POSTS
Hello,

It sounds like you have too much oil in the system. You can't remove all of oil with a vacuum down and recharge but to be sure turn the system on and wait 5 minutes then grasp the outlet tube (large tube) at the fire wall to see if it is cold. This guide can help us see whats going on:

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

Your pressures are good but it will act full with too much oil FYI. Please run down this guide and report back.

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Monday, July 13th, 2020 AT 7:07 PM
Tiny
2HS
  • MEMBER
  • 8 POSTS
Hi Ken,

Appreciate your time and help.

I did an A/C flush of the system, replaced the condenser, TXV, drained the compressor oil, and then added 4 Oz of PAG 100 oil before pulling vacuum and recharge. Do you think 4 Oz is not the correct amount? I got that amount from AutoZone and a post from another forum:

https://www.subaruforester.org/threads/a-c-compressor-failure-how-much-pag-oil-does-the-system-take-solved.805834/

One thing I did noticed was when I drained the compressor, there was not 2.7 Oz recovered. There was maybe about 1 Oz at most. I thought the oil may have been trapped in the evap core and the old condenser and would be cleared with the flush. Would that be the wrong assumption?

If you think I added too much oil to an empty system, what would be the best appropriate next step? Also, how much oil should I’ve added? I’ve read several articles and watch videos that even an evac and recovery of the system does not remove the oil. So sounds like I may need to do another flush of the system again?

Thanks for your reply and help.

-2Hs
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Monday, July 13th, 2020 AT 10:46 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
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Yes, the best way to tell is to vacuum the system down and open it, there should be some oil but it should not be dripping out. I would do the low side tube to judge. Can you please shoot a quick video with your phone so we can see what's going on, that would be great. You can upload it here with your response.
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Tuesday, July 14th, 2020 AT 10:45 AM
Tiny
2HS
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Hi Ken,

Would you please provide specific sequence of steps so I am perfectly clear. Assuming I’ve performed an Evac and recovery already and the system is ready for opening.

Thanks,

-2Hs
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Tuesday, July 14th, 2020 AT 11:32 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
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Once the system is empty please follow this guide:

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

Remove the lines at the compressor image below and video the inside of the compressor and refrigerant lines please. Upload the video in your response. Check out the diagrams (below). Please let us know what you find.
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Thursday, July 16th, 2020 AT 10:34 AM
Tiny
2HS
  • MEMBER
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Hi Ken,

Sorry for the delayed response. I don’t have an update for you as the vehicle has not been available for me to work on. If/when I get to work on it in the future, I will let you know how it turns out. I wanted to thank you and Joe for all the help.

Stay well and be safe.

-2Hs
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Monday, August 31st, 2020 AT 4:26 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
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Please let us know what you find. We are interested to see what it is.
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Monday, August 31st, 2020 AT 2:27 PM

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