Some has already told me my unit on my 1988 Regency is r12.Can someone help? and tell me what the high and low pressure should be.

The proper pressures are dependent on ambient temperature and relative humidity. However, short of digging out the charts, go for 30 psi on the suction side. You should get at least 150 psi on the discharge (but 250 would be better)

As Rusty points out, the hi/lo pressures vary with temp and load. My 86 had an R12 system also (I took it out and use my roof ACs instead) Mine had a standard sight glass in the high pressure side. If you fill until bubbles are gone in the sight glass you'll be real close without having to worry about the ambient conditions.

R12 is getting pricey and my system had leaks. Rather than fix the leaks and recharge I took it out. I can run the generator and AC on the fly and put less heat load on the old 454, as well as less gas through it.

In my case there was another advantage. By removing the AC compressor I was able to run 2 identical belts on the power steering pump, which is critical to both steering and (Hydroboost) brakes. Having 2 belts and no other loads should reduce the chance of failure greatly. Good luck with your system!