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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
    Commented Apr 6, 2022 at 11:18
  • I would also check the AC system related relay switches and replace if necessary. A leaky or clogged evaporator coil is also a good theory as suggested mostly. Visit the dealership for an appointment to checkup on the AC system components such as the gas pressure, leaks, temperature sensors, and relays. I do not know how good ford system diagnostic scanners are. But for mb star scanners unearth a needle in a haystack. Good luck.
    – Lawyer Aidroos
    Commented Apr 1 at 0:19

3 Answers 3

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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
    Commented 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
    Commented Apr 5, 2022 at 14:10
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    No, the heater is just a radiator with hot coolant flowing through it.
    – HandyHowie
    Commented 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
    Commented 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
    Commented 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
    Commented Jun 30, 2023 at 10:50
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Joined just to answer this even though it's old bc i had same issue and i couldn't figure it out or replicate for a shop and it drove me nuts.

I have an 05' ex with similar symptoms--ac works ok initially but after long trips turns into a loud roaring noise and you lose air out the main vents. I think you have a small vacuum leak that causes the vacuum pump to overheat/fail during long trips. Here's why.

As everyone knows if there is a large vacuum leak, the AC will just kick out of the defrost. But if there is a small leak, I now know the vacuum pump can almost keep up by running the whole time (you can't hear over the sound of the engine) so that you get 80% air from the front vents, but don't really notice that 20% comes out of the defrost. so i think over a long trip the pump overheats and you lose vacuum, which causes air to come out defrost.

my vacuum leak was a hairline leak in the grey 1/8 tube going into the heater core valve at the top, back, of the engine bay.

if it was my issue, check to see if their is any AC leakage out of the defroster. if so, i bet you have a small vacuum leak. repairing it should prevent the failure on long trips if it's what i dealt with.

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  • The AC works well to begin with, and if I cycle the AC off occasionally until it stops blowing cold, the problem seems to not arise. I figure this would be because ice would have an opportunity to melt off. Would that be enough to keep the vacuum pump from failing on long trips?
    – Alex Estrada
    Commented Oct 23 at 15:13

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