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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.

Pᴀᴜʟsᴛᴇʀ2
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Alex Estrada
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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 06 '22 at 11:18

2 Answers2

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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.

HandyHowie
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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 05 '22 at 08:46
  • How does a vehicle with 2 zones affect this? The rear vents seem to still work. Thanks. – Alex Estrada Apr 05 '22 at 14:02
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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 -https://www.autocoolingsolutions.com/ac-block-off/2004-excursion-rear-ac-block-off-kit – HandyHowie Apr 05 '22 at 14:10
  • Oh, okay. So should there be a heating element somewhere on the fins that may be faulty? Is there a component that I could test? – Alex Estrada Apr 05 '22 at 15:17
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    No, the heater is just a radiator with hot coolant flowing through it. – HandyHowie Apr 05 '22 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 05 '22 at 18:04
  • Been there, done that. Yes, the more think about it, and a few troubleshooting websites listing the diminished airflow symptom, I too, think this is the issue. Hopefully, I can find time this weekend to clean out the fins on the evaporator, and check the drain. – Alex Estrada Apr 05 '22 at 18:25
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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 05 '22 at 19:56
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    I have had this same issue, and until it is properly fixed, found that you can reduce or delay the occurrence of it by running your fan at maximum from the start. The increased airflow helps to prevent freeze up from occurring. – Glen Yates Apr 05 '22 at 20:49
  • @Z4-tier, oh no, haven't used the AC but once this year yet, but didn't want to go into this next summer camping season with this issue again. – Alex Estrada Apr 05 '22 at 21:37
  • As a quick addition, I am not sure if Ford does things similarly, but I had this issue on a VW once. They actually have a sensor at the evaporator that detects when it's about to freeze up and throttles back the AC in that case. Apparently, the sensors design was faulty in my particular case, but of course it can also happen that the sensor just fails otherwise. VW had a revised design that fixed this issue. – PhilippNagel Apr 06 '22 at 13:15
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    A clogged filter can cause the coils the ice up. – Bob Jarvis - Слава Україні Apr 06 '22 at 15:30
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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.

Jupiter
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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 '23 at 10:50