By Mike Dailey
Last year I upgraded and rebuilt my Pantera A/C system around a Sanden rotary compressor. The design of the heater valve does not totally shut off the hot coolant to the heater core when the heater knob is in the full off position on 1971 model car. This creates heat in the heater core when the A/C system is trying the cool. The solution is to add a shut off valve in the heater coolant feed line in the engine bay that connects to the heater feed line.
After some scrounging around at my local Home Depot I found a Mueller 1/2" Ball Valve for $6.97 and two Watts 5/8" to 1/2" A-493 MIP Adapters for $1.94 each.
View of the Mueller 1/2" Ball Valve and Watts 5/8" to 1/2" A-493 MIP Adapters . Teflon tape was used to seal the threads.
The next problem was how to cut into the heater hose with coolant in the system. I solved the problem by barrowing two clamps from my neighbor that is like Norm's brother.
View of Norm's clamps
I used the clamps to clamp the heater hose in the engine bay so I could cut the hose and add the valve without the coolant leaking. One clamp was clamped on the upper part of the hose and the other on the lower end of the hose.
View of the upper clamp
The valve was added to the supply hose that feeds from the block next to the thermostat housing. After the clamps were in place I used towels to keep the small amount of coolant in the hose from running down the firewall while I cut the hose. The 1971 Pantera has the heater tubes located higher on the firewall than the later cars so I had to mount the valve higher on the hose than it would be on the later cars.
View of the valve installation
The best view of all! 40 degree A/C outlet temp when the outside ambient air temp was at 95 degrees. Next I will be installing a valve on the heater return hose.
Update:
After looking at the completed job I decided that running the hose over the top of the engine main coolant exit pipe was Mickey Mouse. I found that if I cut about 4.5 inches out of the heater hose it was possible to route the hose and shut off valve next to the heater return line.
View of the improved valve installation