A/C cooling fan question

[LS1CHEYENNE]

I have the S & P a/c setup on my truck and it's been working fine since I charged it back in May but it began freezing up lately so I hooked up my gauges and put a little freon back in . But this time I decided to try something different - I fished the hoses up through the hood by my windshield , closed the hood and went for a drive . I was surprised at what I found . The high side pressures stayed below 150 psi as long as I was going 20 mph or above . If I slowed below that it would creep up eventually to above 200 psi .This is without the fans running . I'm told at around 300 to 350 psi you can blow something out like an o ring or a hose . So this is my question - why do the fans need to run 100% of the time when you're running down the interstate ? Why not keep it toggled or relayed somehow to only run when needed ? Mine is on a toggle and I always keep it running with the a/c on but now I don't think I will if I'm moving down the highway . I also keep a temp gauge in the vent and it always runs at about 45 degrees . Turning the fan on or off at highway speeds didn't change this temp reading and seems to support my theory that the fans are a waste at any speed above at least 40 mph . Anyone else with experience on this ? Thanks

[RedHeartbeat]

Mine freezes over some times, too, but it did it with the old system before the change over. I don't know if there is something inside the evaperator core to turn the system off when it ices up or not and if maybe I circumvented that part or not.

[LS1CHEYENNE]

If it's freezing over then it must be low . I knew mine was because the vent temps dropped below 32 F. When going down the road the low side pressure dropped below 20 psi . That's too low . I'm told it should stay close to 30 psi with the engine running above idle . Are you using 134 a or a newer cocktail ? I'm using ES12a which is a hydrocarbon base and gets colder than 134 . That's why I usually get vent temps of 45 degrees and with less drag on the engine . Nice and cold and better gas mileage

[RedHeartbeat]

134a. I may have to check into the other. I bought a vacuum pump so I can service it any time I feel like it. Maybe I'll check into the ES12a if it can save some mileage. I don't know if I'm losing MPG running mine or not. Maybe I'll read up on it on the net.