Subaru Air Conditioning Explained
Typical Subaru Air conditioning Problems explained.
The Air conditioning (AC) system in your Subaru is made up of the following.
A compressor, Condenser, Evaporative (Evap) core, Expansion valve, receiver dryer, hoses and lines, thermo sensor and the controls. Inside the car there are a series of ducting or blend doors and their respective controls. I am not really going to give a class on how the ac system works I will save that for another article.
Anytime you notice a situation where the Ac system isn’t blowing cold air, there is some sort of a problem with the ac system. Driving down the road at 60 mph brings in a rush of air that may feel cool to you, just like standing in front of a box fan in your house provides some temperature decrease. But if the ac doesn’t actually feel cold there is a problem.
When the ac system is in fact not performing as it should a diagnoses must be performed. When an ac system has a low charge the performance will most definitely suffer. But its also possible to have a ac system that has a full charge and not blow cold as well. The possibilities are many and in some circumstances the problem may be hard to diagnose or have more than one issue.
Adding to this is that it is normal to lose about 2 ounces of R134a out of an automotive system every year with no real leaks. So on the one hand the system could just be low enough to not function correctly after 4 years with no real problems or it can be low as a result of a leak.
I wanted to point out some of the current issues we see.
The 2000 to 2004 Legacy and Outback suffer from leaks at the 2 Ac hoses one from the compressor to the condenser and one form the compressor to the Evap core. This causes the system to run low or empty. It’s a very correctable situation and if not fixed properly will just cause the R134a gas to leak back out causing the problem you were trying to fix to reoccur. To find the leak test equipment is needed.
2002 to 2003 Subaru Impreza, ( all models and trim levels) has an issue where the Evap core can ice over as a result of a design issue to the system, Subaru has issued a service bulletin about it. The fix is a new thermosensor (which is located in the Evap core). This requires taking the Evap core out of the vehicle which is partially removing the dash components on the passenger side. I usually suggest replacing the expansion valve at the same time.
The 2001 to 2004 Outback with the H6 has some of the same leaky hose issues that plague the 4cylinder models.
The newer Ac systems (2005 and up) are smaller than they have been previously and even just a slightly low charge can affect the performance.
Typically speaking we only think about the Ac system when it isn’t working correctly, but the reality is, it really should be serviced at least every 4 years. As the system loses some of the refrigerant as part of what is considered normal, it is replaced with air, which creates moisture in the system, which periodically needs to be removed through a process called evacuation, which involves hooking up a vacuum pump and putting the system into vacuum, the system should than be re-oiled and recharged with refrigerant and this good maintenance can help ensure your ac system will work when you want it to.
Thanks for reading
Justin
In your article you state that the 2000 to 2004 Outbacks suffer from leaks at the A/C hoses from the compressor to the condenser and from the compressor to the evaporator which cause the system to run low or empty, and that 2001 to 2004 Outbacks H6-3.0 have some of the same leaky hose issues. I am the original owner of a dealer serviced 2002 LL Bean wagon with 100,550 miles.
I am wondering what the “…very correctable situation” is, and what the proper fix is to which you refer.
I am unable to locate any relevant TSB or recall on this issue and would appreciate an elucidation of your findings on this matter.
Hello Robert,
Very correctable means it can be repaired, it isn’t overly hard, expensive or difficult for a Professional Technician to take care of. It wont cost thousands of dollars, take weeks and be hard to figure out.
TSB’s cover less than 1/2 a percent of the issues we face on Subaru’s and are typically about Subaru alerting the Dealers when something is common to cut don’t on Warranty claim labor billed back to Subaru by the Servicing Dealer, so when things are learned after the cars are out of warranty you will never see a bulletin only safety recalls and a few notices if it affects a system that has the potential to be a safety issue.
On the H6 platform from 2001 to 2004 both the low and high side lines/hoses tend to leak. You can look for oil residue at the crimp fitting areas of the hoses or if you have test equipment you can test for the leak.
There are other issues we deal with such as climate control issues, leaks at the Evap core, compressor clutches that fail, relays etc.
Justin
I was quoted about $450 to replace the hose from the condensor to the compressor, $650 if I used any refrigerant with “stop leak” in it. The hose itself, from the dealer is $167!! That seems expensive to me.
Stop leak is a terrible idea. Do you mean dye? I cant imagine a Good Subaru dealer suggesting any form of stop leak in any system you car has.
As far as price, there is the ac service and the labor to replace the hose, not sure about the price on the hose either the MSRP went way up after the Tsunami in Japan.
Justin
My 2004 Legacy has A/C which is nice and cold until outside temp goes over 85, then it will blow warm. After a short stop it will once again run cold.
Dealer tells me it is the thermosensor. Trouble is it is on back order for over two months now. I think it is just that the clutch sticks when it is warm.
Help! Its been a hot summer for not having A/C.
Ward,
I really dont know with out looking at it what is wrong, it would just be a guess. But I really haven’t seen to many clutches work intermittently on Subaru’s.
Justin
Hello this forum is first rate.
“The 2000 to 2004 Legacy suffer from leaks at the 2 Ac hoses one from the compressor to the condenser and one form the compressor to the Evap core.” Our car is 2003 Legacy GT
This is my problem and talking to an AC mechanic mentioned you can replace o-rings vs the hoses. Do you agree? If not do you know the oem part # for the hoses to replace?
Thanks again
Hi Mario,
The Subaru Dealer can look up the part numbers by VIN Number. Or you can look it up your self at opposedforces.com. Because the hoses tend to leak where they are crimped to the metal lines, your guy needs to look on the bottom side of the hose for oil residue. You may get through this year with just the o-rings but it may also leak out in a month, in my opinion because the hoses are so problematic its better to make complete repairs that wont let you down.
Justin
If the a/c compressor is on with the a/c buttom off and the fan off,
What can cause that problem?
Hi Edwin,
The ac compressor also engages whenever the defrost mode is selected. If thats not the case then the switch could be at fault, the relay could be sticking or the compressor clutch could be gapped to closely and as a result not disengaging properly.
Justin
Hi Justin,
I’m installing a new receiver-drier in my 2002 Outback. The Haynes manual recommends adding ~10ml refrigerant oil to the new unit before installing. Does it matter which side I add the oil to (from condenser OR to evaporator)?
Thanks
in my 02 WRX, the refrigerant leaked out and line from compressor to condensor was leaking. I replaced both the line and the compressor and recharged with the 16oz can of R134A from Autozone. The clutch does not kick in on the compressor even though there is pressure in the system. When I manually force the a/c clutch to (give the wire +12v) the line from compressor to condensor gets super hot. What is happening here? should the system be bled or put on a vacuum machine? please advise.
Thanks
Ac repairs in the driveway are tough and most likely wont last, you do need to evacuate the air and moisture from the system prior to recharging it in most cases. You may have a pressure build from to much air or a pocket.
Justin
I have a 2003 Impreza Outback. I have been having a problem with the ac cutting out after driving for a while on hot days. The ac was left on, even though the fan was blowing warm air. The coolant temp spiked and then cooled off after turning off ac button. The ac works after car parked for a while then cuts off again after heating up. The rad is full. Both fans are working. Any ideas?
The Ac system needs to be evaluated locally there is a TSB for the Evaporative core freezing on the Impreza Platform of that Era and some updated components, it is not a DIY repair.
Justin
Hello! The A/C on my 2004 Legacy cuts out after 10 minutes or so of driving. I just had it serviced, there are no leaks, the freon and everything was replaced. The problem remains, when the engine is warmed up and you open the throttle, the pressure in the system decreases and the compressor turns off and stays off until you reset the A/C and wait for another 5-10 minutes. The A/C works fine at idle for a while, kicks off as soon as you start driving.
Mike,
There are many possibilities there is just no way for me to guess from here. There is no Freon its R134A, and an AC service doesn’t include everything, typically its no more than a preventive maintenance service like changing your oil. Overcharge can cause your symptom but so can a failed compressor clutch, I could go on like this for a page of could be’s, your’e just going to have to go back and have a proper diagnoses and take things from there.
Justin
I replaced the high side hose in my 04h6 recharged the system and drove about 700 miles parked for 2 days and the system was empty. I drove home replaced the o ring and added some teflon type tape to the threads at the fire wall and drove it problem free for a month. I just drove 300 miles with the ac on worked great parked for 2 days and it was doa on the return trip. I understand the leaking hose idea but why when it works fine for a month will it leak out after a long trip?
The leaks are brought on by pressure and flex, the more those things happen the more it leaks out.
from this response it is implied that there is more pressure building up the longer you drive? that doesn’t make sense if that were the case then there would have to be a pressure release valve in the system and we would have to recharge the system like filling a gas tank.
Ok, so here are some of the aspects of the ac system you are not familiar with. You can go buy a set of Ac pressure gauges and hook them up to your vehicle you would have a better understanding of how the ac system in your vehicle works at various speeds and temperatures. Ill do my best to try and explain it, but Its hard to teach you in a few paragraphs something you should spend a minimum of a few months in school for just to learn all the aspects of the AC and climate control systems before you will have a real good understanding of how it all works than spend 5 years in the field gaining real world situations before you are really an expert.
Temperature affects pressure in your ac system just like it does in air your tire, which is why you always check and set tire pressure cold, as when the tire rolls down the road and heats up the pressure will increase do to the temperature increase creating expansion of the air.
In your ac system you have a gas called R134A, pressure is built up as the Ac compressor compresses the gas creating a temperature increase and then the pressure is dropped rapidly the sudden drop in pressure is what actually creates the cool air, AC is NOT making something cold, its creating pressure and temperature and than drastically removing both.
While driving down the road at a higher rate of engine speed the Ac compressor WILL build more pressure than at idle or driving around town. The Ac compressor will engage more frequently creating more instances of pressure build up, the car driving down the freeway at higher speeds will FLEX more than at idle while at a stop light.
PRESSURE & FLEX CAUSE THE HOSES TO LEAK.
There is a high side pressure relief valve that will cause the system to “vent out” the dangerous gas that is R134a but only when the system reaches a pressure that is to excessive, this pressure value is much higher than the normal operating pressures of an AC system. Typically only overcharging or a defective Expansion valve will allow the pressure relief valve to engage. The primary reason the Relief valve is there is to prevent explosion under extreme pressure, and since part of the AC system is in the Cabin of the car with you it would be bad to let the evaporator core explode while you were in the cabin with it , and in older cars could at the worse kill you. With out a relief valve pressure would continue to build and vent or explode out which ever was the weak spot in the system, and that could vary by the car.
Again higher pressure at higher speeds is a Rule in an automotive AC system. But not above a specification to the point of Vent out just higher gauge readings and more frequent compressor on times.
If you have a slow leak in a tire do you think it will leak out faster with more air in it or with less?
The first thing you learn at tire store (if its a good one) is that when looking for a slow leak that is difficult to find, first inflate the tire to the Max PSI to find it, which poses no risk as long as the tire is not mounted on the vehicle and driven, and a cage is used if a split rim. As a leak wil show up more clearly at 50PSI than 30PSI, it has no choice its a a rule of pressure.
Because R134A is harmful to the environment, we really don’t want it to continue to leak out. An Ac system that is low can also lead to AC compressor damage as well.
I hope that helps you and any one else that reads
Justin
Hi Justin,
I recently had my 02 Outback AC system serviced (replaced receiver-drier and leaky discharge hose) and while the air is blowing cold and all seems fine, I’m now hearing a brief foghorn noise during operation and almost always when I turn the AC off. One suggestion is that the noise may be coming from the expansion valve. Any other possibilities? And if it is the expansion valve, can I live with it and the noise or must the valve be replaced ASAP (having to open the system again and replace the expensive drier, again!)?
There just isnt anything I can offer without hearing the noise, it could be one of many things
Thanks for replying Justin. Just tapped the outside of the expansion valve (like hitting the side of a television set) and so far, no more noise.
Hey Justin,
Thanks for the info. I have an 01 subaru legacy wagon. I drove it fairly hard for over two hours yesterday. As I was finishing my drive I pulled into a parking lot and scraped the bottom behind the front tire. I noticed a considerable amount of drip coming out of what looked like the frame on the passenger side of the vehicle just behind the passenger seat. It seemed to be water, no oil residue. I thought it may be a tube that was running down the beam and then I noticed a slight crack in the beam where the fluid continued to drip from. I left it at a mechanics in town and got a ride. Does the AC leak from a fabricated crack where the tube ends in the frame or is this something out of the ordinary that needs to be addressed. Thanks for any advice
Hi – I am really needing some guidance on my Subaru Outback 2005 A/C issue. During the span of one minute it will blow cold and then cycle very briefly to less cold or even warm (the hotter the day the warmer it blows), then back to cold. I have replaced the A/C fan as suggested by the mechanic, this did not fix the problem. It was also charged at this time and a dye was used to check for leaks. Nothing. The second time around the mechanic replaced the compression valve, stating that he too noted that the pressure would decrease during this warm cycle. He then also recharged it. Driving it today I can tell that it is better but when holding my hand up to the vent I can feel it cycling again – cold, then warmer, cold again. I anticipate that this problem will get worse as I lose this fresh charge. Which is exactly what happened the first time I took it in and got it charged. Any ideas?
Hi Alison,
I am afraid there just is not anything I can do from here, I need hi side and low side gauge readings and temperature values to try and diagnose an AC issue such as the one you have.
Justin
Hi Kane,
There are 2 hoses most likely the other one is leaking.
Thats just a guess based on the info provided.
Justin