Signs of a Bad or Failing AC Compressor Relay | YourMechanic Advice

Car air conditioner works intermittently

Car Air Conditioning / May 3, 2020

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.