Air Conditioning Quits Blowing Hard at Highway Speeds

[Josh1986]

I'm wondering if anybody else has experience with this issue.
The air conditioning blows ice cold, but after a few hours of driving it doesn't blow hard anymore. The fan is still blowing at the same speed but the air isn't pushing out like usual, like the vents are closed but they aren't.

It's usually when we are traveling at highway speeds (65 MPH or above) that it happens. When you slow down to city driving again, it seems like the air conditioner can "catch up" again. Once again, this only happens after driving for at least two hours solid, we don't have issues on a 45-minute trip on the interstate.

I know there isn't a cabin air filter in the 1998 Expedition XLT, but any other suggestions?

We have a 1998 Expedition XLT, 4x2 with air ride suspension.

Thanks in advance!

 

[05_Expedition]

That sounds like the AC system has been over filled. Too much free-on will cause this, it doesn't have enough room to move freely.

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[stamp11127]

I'll go in the other direction, too little refrigerant lowers your evap temp and will cause the evaporator to ice up. One way to check is look for ice on the lines going to the ac by the firewall.
One other possibility is that you are on max ac the entire time, the cabin is getting very cold and the evap is icing up from the low temp in the cabin.

 

[Josh1986]

In response to stamp11127, we run the A/C usually on the regular A/C setting (not Max A/C) with the fan speed on one of the lower two settings. The rear A/C also runs.

I hooked up a freon refill gauge and the gauge shows its at the yellow "Alert" and red "Danger" divider line with 65 PSI. Assuming the gauge is correct with the vehicle running on Max AC and full fan speed.

I've owned the Expedition for almost four years and never refilled the freon. It has had this issue for almost the entire time, but we rarely drive it that long that it's never been an issue since it starts acting up when we're almost there.

We will be taking a 6-hour drive in a week. I will try to investigate this week locally if the freon is overfilled. If it's still doing the same thing after driving several hours, I will look for signs of ice near the firewall.

Whatever ends up happening I will report back as events unfold.

 

[1955moose]

Hook up r134 gauges, their are outside temp and pressure charts printed this week. Sounds like your overcharged. Try evacuating off a little, preferably safely with A/C recharge/ evacuate equipment. We never like to discharge ac refrigerant into the atmosphere.

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[stamp11127]

Before venting/reclaiming some of the refrigerant, hook up a set of ac gauges and note the outside temp, high and low pressure readings at idle. You may be able to borrow a set from an auto parts store. AC should be set on max with front and rear blowers running on high.

Your charge may be correct and the compressor is failing, letting some of the high side pressure bleed over to the low side. Or, you could have too much refrigerant in the system like 1955moose stated.

With 65psi on the low side it isn't freezing. Look at the pic below. The left gauge has multiple ranges on it. The center band is temp in F. The outer range is low side pressure. The low side pressure and temps fall pretty close to one another.

https://www.google.com/search?q=low...AUICygC&biw=1680&bih=919#imgrc=RSy1xKtE1eKPTM:

So we know your low side pressure, we need to know the high side also to determine what the compressor is doing.

 

[gregjenny9502]

The way I am reading this, sounds like a vacuum leak. Fan is still blowing hard (by sound) but volume of air coming out is restricted. Mine does the same thing. Works fine at idle and constant speed but at acceleration you can hear the fan still blowing but no air coming out of the vents. Let off of the gas and in a few seconds back to normal. I replaced the vacuum canister but no change. I now have to look for a vacuum leak somewhere else now.

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[johnboneske]

In response to stamp11127, we run the A/C usually on the regular A/C setting (not Max A/C) with the fan speed on one of the lower two settings. The rear A/C also runs.

I hooked up a freon refill gauge and the gauge shows its at the yellow "Alert" and red "Danger" divider line with 65 PSI. Assuming the gauge is correct with the vehicle running on Max AC and full fan speed.

I've owned the Expedition for almost four years and never refilled the freon. It has had this issue for almost the entire time, but we rarely drive it that long that it's never been an issue since it starts acting up when we're almost there.

We will be taking a 6-hour drive in a week. I will try to investigate this week locally if the freon is overfilled. If it's still doing the same thing after driving several hours, I will look for signs of ice near the firewall.

Whatever ends up happening I will report back as events unfold.

Mine does the EXACT same thing, and mine is charged properly... When mine does it, it usually takes 40 to 50 minutes for it to happen, I "select" defrost for about a minute and then go back to vents, and all seems ok. It blows ice cold, and fan speed doesnt change, but after awhile you cant feel the air anywhere: not on the defroster, floor vents or dash vents...then after I select defrost for about a minute and then go back to dash vents all is fine for another 40 to 50 minutes...

 

[Josh1986]

Mine does the EXACT same thing, and mine is charged properly... When mine does it, it usually takes 40 to 50 minutes for it to happen, I "select" defrost for about a minute and then go back to vents, and all seems ok. It blows ice cold, and fan speed doesnt change, but after awhile you cant feel the air anywhere: not on the defroster, floor vents or dash vents...then after I select defrost for about a minute and then go back to dash vents all is fine for another 40 to 50 minutes...

I'll give this a try. Air seems to blow out of the vents ok when we turn the air conditioning off after it feels like there's no air flow from anywhere, but usually we turn it off and crack open the window.

It also seems like once we get off the interstate, after a few minutes the air flow seems normal again too because we're driving at a slower speed.

 

[1955moose]

Here's a dumb thing to check. Be sure your air conditioning condenser is clean and free of debris. You'd be surprised how many ignore the obvious. Crap around the condenser and you cut down on flow and cooling.

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