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Discussion Starter · #1 ·
How long should it take for low and high side pressures to equalize after vehicle is off?

Having AC issues and it takes 120 minutes for high and low pressure to equalize. Initial Static pressure is 100 psi on both sides. At startup low goes to 35 psi and high to 200 psi. Vent temp mid 47 deg F. All good. Shut off vehicle for 10 minutes to run into shop and no cold air. Running Pressure now 27 and 210 psi which shuts off compressor due to low pressure according to the service manual.

Shut off engine and read pressure at 10 20 30 60 90 120 minutes. Pressures Did not return to equal until 120 minutes. Rapidly equilibrate first 50 psi in 10 minutes then more slowly afterward.

Is this normal or do I have a bad expansion valve?

Thank you in advance.
 

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Discussion Starter · #2 ·
Here are the data that I collected while I was troubleshooting. All pressure are psi and all temperature are in Fahrenheit units. Both radiator/condenser fans were running. Front and back water was dripping under the vehicle. Time 0 was a 10 minute run after vehicle had set overnight. Time 1 was after a 10 minute rest following Time 0 run. Likewise Time 2 was after a 10 minute rest from Time 1. Rest 10-120 was static pressure engine remaining off, following the 10 minute run T2. Time 3 was a 10 minute run following the 120 minute rest following Time 2.

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Those are symptoms of overcharged, restrictions in the condensor or discharge line. Dirty or damaged fins on condensor would also cause high vent temps, but wouldn't effect your equalization. My guess is the condensor is restricted.
 

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Discussion Starter · #4 ·
Thanks @Slvr7. So my first path is to pull coolant out of the system and ensure the correct amount is recharged. If that doesn't fix the issue, then work on the condensor (not the evaporator, nor the expansion valve, which I wasn't looking forward to) and discharge line. Where is the discharge line? I know old tractors and other makes of pickups, but am a novice Piloteer.
 

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Yes, I would verify charge, although I don't believe it's your issue. I think you have a restricted condensor, there is a filter at the bottom of the drier( round tube on the side of the condenser), I would check the filter and make sure the desiccant bad hasn't ruptured. The discharge hose is the hose between the compressor and condensor.
 

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mmm, for 75F ambient, even with high humidity, at idle, high cabin fan, RECIRC and front doors open, I'd expect a LOW side 40-ish psi and HIGH side150ish if both radiator fans are blowing normally. Wouldn't suspect condenser restriction as my first guess--you can check the condenser temp variation across and down the fins using a cheap IR gun, or a DVM with temp probe. The rear air unit has its own evap, I think. Is the duct temp abnormal at the middle console ducts when the compressor is running? If those temps are good, then I'd lean to a dodgy front expansion valve.
 

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mmm, for 75F ambient, even with high humidity, at idle, high cabin fan, RECIRC and front doors open, I'd expect a LOW side 40-ish psi and HIGH side150ish if both radiator fans are blowing normally. Wouldn't suspect condenser restriction as my first guess--you can check the condenser temp variation across and down the fins using a cheap IR gun, or a DVM with temp probe. The rear air unit has its own evap, I think. Is the duct temp abnormal at the middle console ducts when the compressor is running? If those temps are good, then I'd lean to a dodgy front expansion valve.
That's also a possibility, and they mimic each other on many of the symptoms. Without line temps and temp in and out of the evap/condensor, little tough to pinpoint. I have put 1 expansion valve on that body style, but many condensors that were internally restricted with the same or similar symptoms.
 

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Discussion Starter · #11 ·
Thank you @AVC and @Slvr7 . I will check mid-seat vent temperature. Also will check temperature down the condenser and line temperature (good excuse to purchase an IR gauge). Will also check the volume of water dripping and compare to my Subaru. Will keep you posted.
 

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Discussion Starter · #12 ·
@AVC and @Slvr7 . Here is some more data for you to consider. Happily the problem repeats and it cycles over the course of 3 hours very nicely. Also good that it was 90 degrees and humid in central Illinois. I compared the 2011 Honda Pilot with our 2016 Subaru Outback and got the attached data. Right on schedule, when Low pressure drops below 28, the compressor is kicked out (but the clutch is still engaged). It takes 150 minutes to equalize the pressure on Low and High side. The rear vent always performed better than the dash vents. I collected water from the evaporator and measured at the end of each time course (in milliliters so it could be measured). The temperature of the Low line going into the firewall of the Subaru was always colder than the Honda. The left side low hose (looking at the firewall from the front) versus the right side low hose at the firewall relative temperature is recorded.

After I finished, I let both cars sit outside in the sunshine for 2 hours to check if evaporator is frozen and would thaw. Just like the T60-T150 time, there was no excessive water release so not thinking that is the problem.

So the question remains, is the expansion valve or condenser the culprit? Thanks in advance for your thoughts.

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Since your cleary willing and able to get data. Measure your front vent temps left, right, and center, if they all match no need to add to the chart. Please add cabin temp to the chart during running conditions. Different points in your data chart point to different issues some indicate a restricted condenser, others indicatea bad expansion valve. Have you verified your refrigerate charge, being low would definitely cause most of the symptoms.
 

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Discussion Starter · #14 ·
@Slvr7 . Will do. In your opinion, which data suggests condenser and which suggest expansion valve? Do the different temperatures of the low side hose across the firewall suggest expansion valve? Does the warmer overall temperature of the HVAC system compared with the Subaru suggest a condenser? I wanted to do this test before pulling the refrigerant in case it was pretty clear the issue, then I wouldn't need to do it twice - once to check charge and again to evacuate the system for the repair.
 

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What were the condenser temps, down and across? You can also put a piece of masking tape on the evap inlet and outlet lines (most IR guns are not accurate measuring off bare metal) and read temps. And using a K-type probe and a temp meter is more accurate.
 

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Discussion Starter · #16 ·
An update - I replaced the expansion valve which was no small feat and took about 3 hours. Recharged the system and it has worked well for the past 2 weeks. Vent temps now holding steady at 46 F. Thank you to @AVC and @Slvr7 for your input and help. This YouTube video helped a lot. Not a fancy video but effective. Be sure to have a magnetic phillips head screwdriver with a long reach. Attaching the blower assembly back onto cowling around evaporator took the most patience.
 

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KenD-

Glad to hear you've "cooled off", lol. As an aside I've got a first gen 2006, 119K miles, that I had A/C problems with in the past that are now fixed, addressed in another thread. On those first gen models with automatic climate control, the A/C system uses input from various sensors such as outside temp, inside temp, blend door position, output temp, etc, to control the A/C system and tell it when to turn on and off (i.e., compressor). There is actually a very simple and useful on-board diagnostic that can be accessed through the A/C controls on the dash for first gen Pilots, unknown if it applies to your 2011. I found it extremely helpful to rule out any electronic issues regarding the climate control system; I believe I put links to info for that in my prior posts here.

Greg
 
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