Dash AC running intermitent

[pitchindad1]

I have a Holiday Rambler 2004 DP, Dash ac worked great leaving south of Houston at 1 pm on Tuesday. Got down the road maybe 30-40 miles it starts to cool less and the further I went the less it cools.
Is there a high pressure switch in the system because when I stopped and let it idle for 5 minutes it went back to cooling great. I keep a small thermometer in the vent so I can track what temps are when running. When I start out it is down in the green, about 50 degrees. I have had problems with the system in the past and have learned you don't overfill with 134a because it will not cool at all. I am thinking I still have to much coolant and the hotter it gets the higher the pressure and then the compressor is shutting down. Any of guys had to deal with this problem?
Thanks

[pitchindad1]

The evaporator is on the rear drivers side. It is clean and I haven't put any gauges on it when it shuts down. It only happens after I have been traveling for a couple of hours. At idle the fans are blowing behind the evaporator so I guess I should stop and check to see if they are blowing when it quits cooling. I will also check to see but my guess is the compressor isn't running when it quits cooling.
It does cool very well at first. Just doesn't make any sense that it would cool so well and then stop, let it idle 5 minutes and it goes back to cooling.

[dakdave]

where is the ac condensor located ? Mine has electric fans on it.Are they both working and is condensor clean? Where ever it is located it needs a good flow of air threw it to heep high side pressure down.Ever put gauges on it when it stops cooling?

[rgatijnet1]

Are you sure that the water valve that controls the heater operation is closed completely?

[pitchindad1]

Yep plenty of air blowing out of vents, it just gets hot after a while. I notice that if the outside temp. is low 90's high 80's it takes longer for the compressor to quit cooling.

[allbrandauto]

I would think that probably you have a evaporator getting to cold an iceing up one sign of that is do you feel air blowing out of vent is reduced if yes than that's your problem 2 ways they control that 1 is a sensor that sits on evaporator to measure temp. other way is low pressure sensor in suction hose