Why is the A/C on my Caterpillar 735 freezing up with low suction pressure and low high-side pressure?

[Robert M.]

I am hoping someone here has seen this before. Static pressure looks normal around 85 psi, but once the compressor kicks on, the low side drops into a vacuum, and the high side only gets to about 100 psi. The drier outlet and evaporator inlet also get really frosty. So far, I've changed the orifice tube, but the pressures still stay the same. Could this be a weak compressor or another restriction somewhere?