'99 Suburban A/C Too Cold

[beltrunner]

So here's the deal...my '99 Sub has developed the problem of the A/C running too cold and freezing up the evaporator.The specs call for the clutch cycle switch to shut off the compressor at 25 lbs-low side, and turn it back on at 45 lbs. With a static pressure of 120 lbs, ambient air temp of 85 degrees, engine idle 1200 RPM: when the system is turned on the compressor activates and the low side pressure stabilizes at around 30-34 lbs...the high side sits at around 180-200 lbs...fan on high, max setting on temp control, the middle-front register reads 28-36 degrees. This is great for awhile until the evap freezes up and airflow is restricted. The lowside pressure will not drop down to 25 lbs to activate the switch to shut off the compressor. I even installed a new pressure cycle switch to no avail since the pressure will not drop enough to activate it anyway. So every half hour or so, I have to manually shut off the compressor at the control panel for about 5 minutes, and then start the process over again. The rear unit is controlled by the TXV and continues to function just fine (rear register temp 36-40 degrees). Any ideas on this? Thanks.

[j cAT]

your problem with what I have found with this issue is insufficient air flow.

now if the air flow is not restricted, flters fan etc clean then this may be a restricted orifice tube.

measure the temp of the evap pipes in and out . they should be the same temp.

your pressures look good.

also remember with high humidity with dewpoints above 70 deg f the evap freezing does occur.

my 2000 silverado runs at 41psi low , 250psi hgh @85 deg f relative humidity @40%.

with these temps the low pressure switch should not shutdown the compressor clutch.

avoid max cool after the vehicle has cooled. use just the AC position.