I put a 4L80E in my 1986 behind the 6.2 with a NP205 bring up the rear. very easy swap from the TH400 that was original. the only thing I had to do was to machine the adapter front housing of the NP205 to fix the 4L80E - $50 at the machine shop
How does the front unit work cooling the whole cabin area? In the big trucks that have two units they run parallel to each other with dual expansion valves. I would think the front unit if designed to cool the entire cab should be enough - have you gone thru it to make sure it is operating at...
I HAVE A 1986 K-30 DIRECT FROM BIG BROTHER SPORTING TWO GROUP 31 BATTERIES AND TWO 100 AMP ALTERNATORS- TRUCK RUNS ON 12 VOLTS AND STARTS ON 24 VOLTS. I NEVER RUN OUT OF ELECTRIC POWER ON WINTER STARTS. NEVER PLUG IT IN TILL IT GETS BELOW ZERO - KEEP THE DUAL BATTERIES!