05 379 A/C question

So I hooked the gauges to my A/C on my 379 as it doesn't seem to be as cold as it should and also temp seems to vary especially when parked.

I had A/C on high recirculate in the truck, the gauges would climb to 48 on the low side and 300 on the high then the fan kicks on.

Once it kicks off gauges drop to around 20 and 100, then the compressor starts, runs around 4 seconds then cuts off. Does this 5 or 6 times the turns on until the pressures build to 48 and 300 again.

While the compressor it cycling on and off the low side will climb to around 40 but the high stays at 100. Gauges never seem to stabilize just constantly climb to kick the fan on. Outside temp is 77 degrees.

Am I low on freon or something else possible or any other info I can give to help get an answer?

 

I have those charts, found them online.

The issue I'm having is it never really stabilizes to get a reading or do I look at its lowest point or highest point as the reading?

 

Ok so found an issue before I can test properly. The fan override switch in my cab doesnt lock the fan on.

Any idea what could cause this. The fan acts normally otherwise just wont lock in with the switch