April historically is the time of year that our focus shifts from the work the cold weather drives, to work the warmer days of summer brings to our shops. At the top of the list is A/C work, and more than one of our readers has made the observation that car owners who typically have no money to spend on safety related repairs seem to have no problem spending money to stay comfortable. And even though the air conditioning systems on newer platforms are experiencing fewer failures than ever, there are still plenty of older systems that need work.
Oh, help me, but I do love A/C work! It’s relatively easy, and the associated flat rates generally are very kind to the A/C technician.
A common concern during A/C season is, “My air conditioning doesn’t work, it’s just blowing hot air.” If you’ve done even a little bit of A/C troubleshooting, one of the first things you do is verify that the interior controls are all working: air flow is controllable from the floor vents to the defrost, the recirculation control does indeed close off the flow of outside air, the temperature door allows the air flow to move from the evaporator core to the heater core before entering the cabin, and the blower is operating across all speeds.
With the system set up to provide “Max” cooling, you expect to feel some coolness coming from the center ducts. If not, it’s probably time to take a peek under the hood to see if the compressor is spinning.
What do you do if it isn’t?
A conventional clutch-driven compressor might not be engaged for a number of reasons. Often, a low system charge is to blame but before we jump to that conclusion there are other causes to consider. How about a bad compressor clutch relay? Or a faulty pressure sensor not allowing the Engine Control Module (ECM) to activate the clutch? Or a mechanical failure in the clutch itself?
These are just a few possible causes. With any diagnostic problem, you start looking for the solution by following a process. First, familiarize yourself with how the system operates and reviewing the schematic. All OBDII systems rely on the ECM to turn the A/C compressor on, and the ECM won’t do that unless it sees that the proper operating conditions are met. Next, a check for Technical Service Bulletins (TSBs) is in order to see if there is a software or component issue the factory already knows about.
Last, I like to check repair databases like the SureTrack system Mitchell 1 has incorporated into their ProDemand service information system. SureTrack consists of a database containing millions of confirmed, real-world fixes that even breaks it down by part replaced and average age of the failures. Users can also post tips or ask help from other community members. Certainly a better alternative then relying on a simple “Google it” approach where the online expert is anything but.
In the April 2015 edition of The Trainer, we’ll show you how to narrow down the list of possibilities using current draw in the clutch circuit. Not only does this technique work for the compressor clutch, it can also be applied to any circuit that is controlled by relay.
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