I have a 2.3L mazda3 with climate control. The A/C works very well in general but when I am highway driving for long periods (more than 2-3 hours), the A/C begins to deteriorate. By that I mean the the fan speed begins to slow down (even tho the gauge reads top speed) and the temp begins to warm up to the point where there is virtually no A/C. Turning it off for 10-15 minutes helps for a few minutesbut it soon deteriorates again. Setting the temp down to minimum (60) doesn't help). Dealer checked it out late last summer and could find nothing wrong but of course, it was operating correctly when I brought the car in.
The problem has repeated on our last long Interstate trip but of course it was Sunday so I couldn't bring it to the dealer while it was still malfunctioning. Outside temp at the time was 85-90. Anyone heard of this problem on A/C with auto climate control.

 

So, you have a GT w/auto climate?
I don't know for sure, but it sounds like the expansion valve may be freezing up causing ice to form and everything else to not work properly in the system.
Either way, it should not be acting this way for you. But as someone who used to work at a dealership and had customers that complained about "intermittent" problems, believe me when I tell you that it is often frustrating for the Service department too.
I suggest, making an open appointment w/your service manager, then driving the car for as long as it takes to act up, then dropping by your dealer. I know this sounds like a lot to go through, but it may be the only way to get satisfaction... unless the symptoms start become more regular.

 

I agree. It's awfully difficult to troubleshoot a problem that's not manifesting itself. Hopefully, the next time it occurs I will be near an open dealership. Thanks for your feedback.

 

FYI....AC systems will cycle on/off in order to avoid freezing up.

 

Unless it's not.....?

 

Same issue here. No climate control on mine though. It has done this 4 times, always after about 2 plus hours of driving, same symptoms. I have had it in a couple of times, but it is obviously almost impossible to fix when you can't reproduce the issue.

 

I agree the dealer should address.

I'm skeptical of the icing theory.The ACsystem is in your engine compartment (obviously), which is very hot ... if you shut the system down for 10 minutes, all the ice would melt and the system would warm up ... I don't see how it could ice up again in just a few minutes. It soundsmore likely tomethat a sensor in the system is reading an overload somewhere (a temperature overload, or a pressure overload), and shutting the AC off.

If your driving for a few hours corresponds with it getting much hotteroutside (ie. you left in the morning, it was only 75, but after a couple hours, it was 90), it would make sense the change in the outside temperature would be the cause, since the load on both your cooling system and AC system would be greater the hotter it is outside.

 

UB, To explain: The icing wouldn't happen in the engine compartment but inside the evaporator housing. The expansion valve is usually mount in, or near the housing and is supposed to regulate the flow of coolant as it's temperature changes up or down. If that is not working correctly and therefrigerant temp gets too cold the evaporator will ice over as moiture in the air is drawn to it. This reduces, or makes air flow past it impossible.Due to the housings insulation itcan take quite a while to for it to thaw.

 

I understand the mechanics of what you are saying. My 2 cents is ...

A dusting of frost on the exterior of the expanion valve (from moisture in the air) wouldbe extremely unlikely to have anyaffect on the valve's functioning. The moving part of the valve is completely enclosed and sealed from the outside air - a littlefrosting on the housing would not touch any moving part. The internal moving part is constantly being lubricated by the refrigerant moving through it.

If the valve was just plain faulty, it would tend to be faulty all the time (since valves are not human, they don't have moods - they either work or they don't).The system would not work fine for several hours, and then stop, due to a faulty valve.

If anything freezes up due to being too cold in auto air conditioning, it is typically the Evaporator. Evaporators need air circulation and drainage (for condensation)to prevent them from freezing. With this in mind:

1) In some cars, there is an Evaporatorcondensation drainage line, that can become clogged. Ifthe M3has such a line, it should be checked to make sure it is completely clean.

2) Is anything blocking the needed air circulation around the Evaporator?

If it's not the Evaporator freezing, then my hunch is its a sensor that is reading a shut off condition (maybe a faulty reading, or maybe a legitimate condition).Something is happeningafter a couple hours of functioning to create a shut off condition.

 

Good .02.
However, it is possible for an expansion valve to work for a time then quit. I'd seen it in the Volvos, and some GM cars using the venturi system(R12 systems) of my youth.
Actually I think you and I are on similar pages, just looking @ it in different ways.
I particularly agree with this statement and what I too was trying to express, "If anything freezes up due to being too cold in auto air conditioning, it is typically the Evaporator. Evaporators need air circulation and drainage (for condensation)to prevent them from freezing."
In modern cars, it might very well be a sensor. billm from the Ms3forums might know since he'sdeveloped a timed bypass for this to help eliminate the "weak A/C" situation.