A/C issues on a subaru

Scott Technician Chico, California Posted   Latest  
Question
HVAC
2015 Subaru Forester 2.5i 2.5L (FB25BA) (TR690)
Stops Cooling At Idle

Hey yall. got a real head scratcher that im trying to fix. this cars AC system works normally during any drive, compressor cycles the clutch normally without issue. the complaint is the customer likes to sit in the car for 10-20 minutes at idle with the ac for misc reasons. but after 10 minutes the system stops cooling, if you tap on the gas and rev it just a bit it will start cooling immediately. let sit for 10 ish minutes and stops. only at idle. idle speed is exactly in spec. this customer has already had the condenser, compressor, expansion valve and evap core replaced at the Subaru dealer. with subaru parts,TWICE. they used parts from known working cars and it still happens. My results with the pressure is when the system is working and blowing cold air. the pressures are 25/220. when it stops the compressor gets audibly louder and the pressures start to drop to 55/155. using a contact dual thermometer i have verified the condenser is dropping 30+ degrees in temp ac… the inlet and outlet at all times working or not. i have also used it to check restrictions in the lines where accessible (ie condenser to expansion valve are the same temp) at this point even i am not sure where to go next. this is a clutch style manual system, no variable compressor. the clutch stays engaged the entire time, heard even the Subaru engineers came to town and where unable to figure it out. wondering if yall have any advice for things i should check.

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Interesting
Freddie Owner/Technician
Houma, Louisiana
Freddie Default
 

does It have an evap core freezing sensor It may be faulty.

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Joel Diagnostician
Soquel, California
Joel Default
 

I AGREE That is the only control probably, the evaporator temp sensor any pressure swith?? . Those compressor are noisy they make some type of whistle ,noise

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JJ Technician
Quincy, Massachusetts
JJ Default
 

Do you lose your volume of air coming out of the vents? Like Freddie said, the evaporator may be freezing over. What speed is the blower on when this happens? With a new compressor we usually advise against idling on a hot day with the blower on high, people who ignore this advice are typically back with a smoked clutch. Put the blower on low and make sure the compressor will cycle normally…

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Scott Technician
Chico, California
Scott Default
 

I actually have not checked if it fails with lower blower speeds, I will try that tomorrow and see if the compressor will cycle or if it changes. I dont notice a airflow difference, its a strange fault as the right as you rev the engine just a bit it immediately blows cold again for 10 ish minutes.

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Clinton Diagnostician
Concord, California
Clinton Default
   

youtu​.​be/OU3HfTM3Dj4 check this out & see if it helps. moisture in the system could cause what you’re describing. it Usually is the result of performing a repair and not maintaining the vacuum long enough to boil off the moisture ingested when the lines are opened. I’ve used enthralpy charts to find issues otherwise missed by just pressure readings alone.

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Clinton Diagnostician
Concord, California
Clinton Default
 

Here’s an R-134a chart You can print it & chart out what’s going on. Good luck

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Scott Technician
Chico, California
Scott Default
 

Thanks! I have not seen this chart before. Good info.

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Joseph Diagnostician
San Antonio, Texas
Joseph Default
 

Subaru Senior Master Tech here. I bet the people who showed up were not engineers but the FSE (field service engineer); you don’t need to have an engineering degree to be an FSE. Shit you don’t have to be a tech to be an FSE. The 2015 Forester was plagued with A/C issues. Evap cores are known for leaking and there’s a TSB for the AC compressor clutch. TSB 10-84-16R. When it comes to Forester…

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Agree
Scott Technician
Chico, California
Scott Default
 

Full manual setup. The clutch works normally during the non cooling event. I will still c… it over and see if it matches tomorrow.

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Clinton Diagnostician
Concord, California
Clinton Default
 

youtu​.​be/bBw8UM7R97M sorry I attached the wrong video this is the one I meant to

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Tom Owner/Technician
Santaquin, Utah
Tom Default
 

I was just thinking what else cood be other than what has been stated. ? May be heater door opening and with a bit of throttle you wood have more voltage . to your mudule if it was a vacum could be loosing vacum i am not sure on this make.

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Albert Owner/Technician
Towanda, Pennsylvania
Albert Default
 

My first thought was the sensors. I'm looking forward to see what the fix is. I'm sorry I can't be of any more help seem like what has been said covers what could be wrong I guess if the TSB doesn't help you'll have to start thinking outside the box maybe the problem is in another system that is somehow connected to the A/C system. As an example : five volt ref getting pulled down because of…

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Kirk Technician
Glenwood, Iowa
Kirk Default
 

following

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Jim Owner/Technician
Charlotte, North Carolina
Jim Default
 

my 2c: Your reading 25/220 during the cooling event. Your reading 55/155 after 10 minutes, cooling stops, compressor making some audio. Clutch is engaged the whole time. Tapping the gas returns pressures/ system back to normal. No variable displacement valve in compressor [?] Based on the info you provided- it would seem likely that the problem would lean towards a compressor or expansion…

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Jason Technician
Lakewood, Colorado
Jason Default
 

Good Morning Scott - OK try this one! Find the resistance spec for the compressor clutch. Plug it into Ohms law to get a current spec, then perform voltage drop and current measurement on the compressor clutch. The clutch may be engaged but, if there is slippage occurring due to an inadequate voltage/current supply, it would make the noise you described, as well has having a drop in pressure…

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Mike Educator
Raleigh, North Carolina
Mike Default
 

Just a heads up. Your calculated value will be different than your measured amp value. When energized the coil will act like an inductor. Basically the magnetic field will create "working resistance". The v drop test will still tell you if the coil is dropping all of the applied voltage.

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Olle Instructor
Albert Lea, Minnesota
Olle Default
 

Not with DC it won't. The magnetic field will not create a working resistance. Only a changing magnetic field will do that.

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Randy Diagnostician
Glendora, California
Randy Default
 

Every body has over thinking . if you jump relay and command clutch on at relay and monitor computer command you will find you problem

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Jason Technician
Lakewood, Colorado
Jason Default
 

I understand that it will not be an exact spec. In my experience it will very plus or minus 20 %. But it’s better than no spec at all. the test is designed to answer only one question. Does the coil have the ability to keep the clutch engaged without any slippage? It will answer that question.

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Stephen Technician
Gallatin, Tennessee
Stephen Default
 

I would like to know what the in/out temp of the condenser and hi side pressure is when working and not. Also the readings for the evaporator in/out and lo side pressure. However, the 25PSI Is low enough to put the evap below freezing. I wonder if that compressor is Suction limiting variable displacement. Or is supposed to? Maybe it’s the wrong compressor?

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Roy Mechanic
Winnipeg, Manitoba
Roy Default
 

Following

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Hollis Technician
Boulder, Colorado
Hollis Default
   

Check out TSB's # 10-84-16R and 15-209-17. Reference part numbers and VIN ID's. They may not directly relate to your issues, but sometimes details are left out in TSB's or they will apply to models not listed due to not enough documented complaints. One TSB references an internal compressor valve issue and the other compressor noise. "Tapping on the gas and holding the Rev's up and it starts…

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Joseph Diagnostician
San Antonio, Texas
Joseph Default
 

I'm a Senior Master Tech with Subaru and would love to help with this complication. Attached is a TSB I want you to read. The Forest received a batch of faulty compressors, read the TSB section on how to decipher the serial number; ignore the VIN requirements, just decipher the AC compressor serial number. 1st: If the AC compressor is good then swap the AC relay with another relay in the main…

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Helpful
Roy Mechanic
Winnipeg, Manitoba
Roy Default
 

Do the newer Subarus disengage the compressor to decrease engine load if needed ? Not saying that is the problem here, but i now remember we had a vehicle last year that had a similar symptom. It was disengaging the compressor clutch to decrease load because the alternator output was low at idle.

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Joseph Diagnostician
San Antonio, Texas
Joseph Default
 

The AC compressor computer does monitor engine load but the compressor will only disengage at WOT

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Frank Manager
Pulaski, Tennessee
Frank Default
   

I would look at the idle speed when compressor stops functioning. Pcm will cut the compressor when the idle speed drops too low. Possibly it is easy as a t body clean. ck the pids for compressor permissions (subaru version) when the cooling stops.

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