Orifice Tube, Mystery Junction Block on 1977 Can Am A/C System ?????
 

Anyone with knowledge of auto air conditioning systems familiar with this mystery "junction block" (#4 in the picture), located along the A/C liquid line?

My car is a 1977 Pontiac Can Am Lemans, that, when I bought it, had an R12 a/c system with a seized-up A6 compressor. I thought the system was original. But, I cannot find any reference to this part in the shop manual, or in any pics of 1977 engine bays. No other reference material shows the small line from the top of the heater box (#2 in the picture) that also runs to the junction block.

#1 is the liquid line from the bottom of the heater box; #2 is the mystery line from the top of the heater box; #3 is the outlet for the line to the condenser; #4 if the mystery junction block; #5 is the replacement elbow for the line from the accumulator to the compressor.

Additionally, there was no orifice tube in the liquid line, which I think should be where the #4 mystery block is. Does this block and extra line replace the orifice tube?

Any help from those with knowledge would be appreciated......

That looks like way too nice a piece to be OEM, tank looks like it was TIG welded by hand.
Design is different than OEM in 77.

After a little more HVAC education and help, looks like the system on my CA isn't original. The mystery block is a TX Valve, used in conjunction with a T.I.V. eliminator kit, and replaces the orifice tube. Not interested in returning the system to stock, so I will be upgrading everything in the system to the updated R134 unit. Thanks All!