I recently bought a 1994 Jeep Cherokee when I bought it the AC didn't work and I checked the fuses have and behold the fuse was blown I replaced the fuse and still nothing pulled the control module out of the dash and found the wiring harness for the power was cut I went to pull the part found a matching one spliced it in somehow the polarities are reversed high is low low as high but none the less I got are moving again but I can't get it to move from defrost it will only blow on defrost if anybody has any tips or tricks I could help me out please let me know

 

Check here for issues

 

Yes, you have a loss of vacuum. Good pics above

 

I almost ran out of breath reading that. Almost.

Like said, vacuum. When the heater or a/c get stuck on defrost, check the vacuum lines as pictured. It defaults to defrost so the windshield can remain clear to see the road ahead.