weird ac question

[otter5555]

i installed a new underdash ac unit in my old chevy truck
bought it on ebay
it has the sanden compressor

for 2 months it worked perfectly, blew 22 degree air, cycled perfectly

then it started freezing up even with the thermostat turned to 0

i suspected low freon but pressures were perfect

i went ahead and removed the freon , pulled a vaccum and put the exact amount specified in again. same thing freeze up in 15 minutes

i bought a whole new evaparator and installed it. freeze up in 15 minutes

i bought a new compressor. same thing. freeze up in 15 minutes.

i pulled belt off of the compressor. freeze up in 15 minutes.

so, here we are. not even a belt on the compressor. 15 minutes driving down the road @ 45 mph and the evaperator is a solid chunk of ice.

i recently made an 8 hr trip and it stayed frozen the whole way.

any ideas?
thanks in advance