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I have a 2004 Ford Excursion with the 6.0 powerstroke. Most the time, the AC works fine, but after a long drive in hot weather, the front AC barely blows out of the vents. The rear works fine, in fact, my wife and I try to point those towards us, but that is underwhelming.

I have already replaced the blower, which made no difference. In fact, I can hear the blower motor ramping when we crank up the fan. It seems as if the air is being caught within the dash. It doesn't make a difference whether we have it blowing at our feet, face, or defrosters. I don't even know if I could really take it in into a shop, since it works initially. We don't typically take it on long drives, unless we are camping, so troubleshooting is pretty difficult. One time, when it happened, we had to sit in a line waiting our turn for the RV dump, and it eventually came back.

None of my factory gauges indicate overheating.

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    It's a long shot, but years ago my car's A/C was misbehaving in a similar fashion and eventually the mechanic found that there were leaves that made it into the vent system and would intermittently block the air flow.
    – MetalMikester
    Apr 6, 2022 at 11:18

2 Answers 2

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The evaporator is the component of the AC system that gets cold. It is located after the blower in the passenger cabin. As it cools the air that is passing over it, moisture condensed on the cold surface and drips out of the system from underneath the car.

Ice can also start to build up on the evaporator, which can start to block the flow of air through the evaporator. This could be what is happening to your system.

Some AC systems have a periodic cycle of heat to stop the ice building up.

When this happens in your car, you could try switching the AC to heating for a while to see if this fixes it.

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    This is the most probable answer. But I would add that that cause of this condition may be a faulty expansion valve.
    – Jupiter
    Apr 5, 2022 at 8:46
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    @AlexEstrada It believe that the rear has its own evaporator and expansion valve on this vehicle, so it is possible that only the front one is freezing up. For example, you can get a kit to block off the rear evaporator -autocoolingsolutions.com/ac-block-off/…
    – HandyHowie
    Apr 5, 2022 at 14:10
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    No, the heater is just a radiator with hot coolant flowing through it.
    – HandyHowie
    Apr 5, 2022 at 17:07
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    You can freeze up a residential/commercial AC unit, too, so it's highly likely that this is the cause. I'd suggest looking for blockage in the evaporator drain system. If the water is dripping out, it likely won't freeze, but if the drain is blocked, water sits and starts to freeze up.
    – FreeMan
    Apr 5, 2022 at 18:04
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    @AlexEstrada running the heater for a maybe 15 minutes continuously after the AC becomes weak is the test. If doing that restores the AC back to normal operation, then this is very likely the answer. That is assuming your heater works OK (and since you're running the AC in early April, I'm guessing the heater doesn't get much use where you live).
    – Z4-tier
    Apr 5, 2022 at 19:56
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Another answer but less likely the solution is that the inside temperature sensor is faulty or being obstructed causing the system to think it's already cool and turns the fan down and temperature up. Or another possibility is the mode door actuators are faulty. HandyHowie has the most likely answer though.

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  • (I'd think this is of course only for systems controlled by a set numeric temperature, really common in fairly new models, rather than the older systems where you manually set the magnitude of temperature change and blower strength? And you'd hear the difference with the fans ratcheting down?)
    – JeopardyTempest
    Jun 30 at 10:50

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