Kinda OT, Dodge air conditioner

Wife and I made a run to the other side of the state yesterday for a big tractor part, took the 97 Ram and lawn mower trailer, 455 miles RT. Got along good until we stopped in Ottawa on the way home for a ice cream. When we left, the air conditioner wasn't putting out much cool air. After a little while we turned it off and drove home with the windows down. I went out this morning and checked under the hood, all looks normal. Started it up and turned on air, blowing cold air. I let it run for 15 minutes or so, put a thermometer in the vent and it read 38°. What happened???
Larry, it rode good, tightened the straps once, it pulled hard in the wind tho!! Chris

I'll bet the evaporator froze up.

Allan

Could have froze the coils due to a bad freeze switch, also possible the clutch is going and slipping when hot, had that happen once, also seen compressor seize then free up when cool. What does it have for a charge in it, pressures balance ok? A stuck expansion valve could cause that as well but obviously you would have seen that as soon as you started it with the gauges on unless it freed itself when sitting

Being overcharged could also do that

I'm with Allan-evaporator froze up.What ever style electric temperature control you have is at fault,I don't know what your Dodge has.Did the air flow out of the vents decrease when you had the problem? Many drivers don't feel the amount of air flow when driving on long trip after cab is cooled down.When you parked getting ice cream,did any water drain out-if you turned it off may have thawed and drained while driving home.38* is kinda cold;your a/c clutch should cycle off before that.If the clutch stays engaged constantly the evaporator will freeze solid,and air flow at high fan speed will decrease to almost nil.This most likely happens at higher rpms such as highway speed,not idle.Mark

One thing often overlooked is the condensor in front of the radiator, they can get enough bug guts or dirt packed into them to cause the a/c to warm up, spray it down with a water hose.

The part of it inside the truck iced up on you and the fan can not push cold air past a ice dam. Be the drain hose is clogged up and so the water had no place to go out and that in turn cause it to ice up

Using it with the air temp cranked clear over on max cold all the time will freeze 'em up too. The evaporator has no time to thaw.

Allan

I'd go with the froze up crowd. But I'll add maybe a switch or relay didn't make contact just once and works since. I've had it happen several times so I know it's possible.

I don't have any gauges to check pressures. Alta said it was dripping on the passenger side, she had her purse on the floor and the strap was wet. I had the temp adjustment dial on max and had it set to recirculate the cab air, just turned the fan down when we were cool enough. Sounds like I should find the drain hose and check it. This truck is not the daily driver, it only gets used in the winter(4 wheel drive) or when I need to use a trailer to haul something. Thanks, Chris

There should be a "cycling switch" that monitors the refrigerant temperature leaving the evaporator. Usually screwed into the accumulator, the tank looking chamber that gets cold, right after the evaporator. It will have a pair of wires plugged on to it. If it is not working, the evap will get too cold and ice over. The switch has a Schroeder valve behind it, so it can be changed without loosing the charge.

Exactly=it is much better to lower(actually raise) the temp and keep fan speed higher to keep more air flow across the evaporator which helps prevent freeze up.Mark

The low side clutch cycling switch it not cycling at 19PSI are its slightly low in refrigerant... If you were sure the charge was not low (but you do not know that) you could bump the cycle switch cut out to 21PSI but I would not go higher...

low in refrigerant yes it will ice up,,, a overcharge, a restricted condense are a slipping clutch will not ice up the evaporator you can bank on that...

The good most clutch cycling switches are adjustable...
You can kill a hog inside the cab...
Some Chrysler operate to good I have seen them freeze up after a few hours of operation are longer and never found a issue with them...

You need to check the vent outlet temp on high blower you did not state were you had the blower set at...

I did a quick check and do not see a evaporator temp switch...

Logically speaking, it is not possible for the system to discharge and recharge itself. That leaves out most high/low refrigerant issues. So, about the only thing that would cause it to stop working and then work fine the next day would seem to point to icing of the evaporator. I also see a reference to dripping inside the vehicle. That would also point to icing.
As to the issue of icing.... The only combination of things that can cause icing is humidity and evaporator temperature below 32 degrees F. or 0 degrees C. So, what can cause that? Usually the low side cutout switch is allowing the low side pressure to go too low. This allows the temperature of the evaporator to go below the freezing point and icing to occur.
One other possibility is a sticking expansion valve. This can cause the system to stop cooling or to cool excessively.
Overcharged system is not a possibility as was previously mentioned. After all, how would it add refrigerant to a working system while in operation???
An undercharged system can cause icing, but the low pressure cutout switch should cause the system to cycle instead of icing.
Therefore, I would look at the low pressure cutout and the expansion valve as the most likely causes of the problem.