Diagnosing air-conditioner problems

Being an old geezer, I remember what itwas like to drive the Central Valley in summer from S.F. to L.A. without A/C. Not fun. So I really like having A/C in our 2012 Honda Fit, and the A/C has worked well on short trips. However, the first time we drove the length of the Central Valley on a hot summer day, after a fewhours it no longer put out cold air, only warm. After a short stop (30 minutes [+/-]), it once again puts out cold air, but only for a short time, then back to putting out warm. When I got home, I changed the cabin filter, whichwas somewhat dirty, but not really bad. Ayear later, we did the trip again, and the same thing happened. But we noticed that it almost seemed to switch from cold to warm rather suddenly, rather than gradually going out. Seems like a real bummer to have the A/C no longer capable of putting out cold air whenyou need it the most. Thanks for any thoughts you might have on this problem. — Richard B

Richard, this will be a tough one unless we get lucky with a stored diagnostic code to point us in the right direction, or you have a heavy buildup of valley bugs or debris that could be inhibiting air flow through the A/C condenser (a large/flat, radiator-like device right behind the Fit’s grille) that is intermittently pushing high side pressure beyond limits. Clean as necessary. Codes would need to be checked within a week or so upon return from the trip. Your Fit monitors the status of many A/C functions and will store a code if something isn’t right. Since this kind of issue doesn’t raise exhaust emissions, you wouldn’t see an illuminated check engine light (check for codes anyway).

Another possibility is to try to goad the fault into acting up closer to home during hot weather, perhaps by running the system as long as possible and/or finding a hilly area to explore, to bring on more mechanical stress. Assuming you could induce a reoccurrence, stopping in a safe place and raising the hood for a visual inspection could really help. We’d want to see if the compressor is engaging, and/or if frost is accumulating on the A/C hose connected between the compressor and vehicle cabin.

At home, engine off, identify the front hub of the A/C compressor and the two hoses connected to it. This will require a good flashlight, as the compressor is the lowermost belt driven device on the front of the engine (right side/front of engine compartment). The front/center face of the pulley is the part we’ll want to later check while the system is running, the outer part of the pulley turns at all times. Now, with the engine running, and hands and flashlight well-back from rotating parts, observe the front face of the pulley with the A/C functioning, then not, to see the difference. Be sure to stay clear of the belt! When the compressor is engaged the entire hub rotates. When disengaged, the front/center part does not. Now you’re ready for a side of the road inspection!

It’s possible under certain conditions such as high temperature, high engine load, or unusual switch/input information, compressor operation may be terminated. Determining the compressor is idle as the fault occurs would be a great start in diagnosing the fault. If you should find the compressor hub is rotating as the system blows warm air, it’s possible the inner liner of the suction hose is collapsing, which may cause visible frosting.

I’m sorry to say the odds of a solid diagnosis and repair are low unless the fault can be duplicated, and a skilled service tech is available to assess the cause.