AC shuts off

[bohmanj]

I have a 1992 nissan sentra andmy air seems to be working normally and gets good and cold as long as I am traveling 45 mph or less as soon as I go above 45mph it starts getting warmer and warmer this does not seem to be rpm related because it does not matter if I am in 3rd 4th or 5th as long as I am above 45 as son as I drop to 45 or lower it gets cold again low side pressure is at 45psi per the gauges any help please

thank youJohn B

[NISTECH]

whats high side?

[NISTECH]

also does it matter if your in recirc or fresh air mode?

[bohmanj]

Sorry I don't have any way to check the high side also it doesn't matter if it is in recirc or fresh air

[NISTECH]

Its hard to say what could be causeing it with out knowing the pressures on both sides when it fails.