Heater Hose Inlet Shut Off Valve Modification 1979 E21

[csvnevada]

I have a 1979 E21 (3/79) with a frozen open heater valve. Currently don't want to tear the dash apart to replace the internal heater valve but would like to do a temporary fix by adding a high temp ball valve to the inlet heater hose on the engine side of the firewall so I can turn off the hot water from reaching the heater core during the summer months. I live in the Nevada desert of the United States and trying to make the interior cabin temperature a little cooler for the hot days of 90 degree F plus temperatures (no AC in the 79).

Will the addition of a ball valve to the inlet hose on the engine side of the firewall create any problems (it should be no different than the factory internal valve) but the ball valve will completely shut the flow off? I did read a post somewhere that said the factory heater valve does let a trickle of hot water through the heater core even when shut off so there is still some heat reaching the cabin interior. So will the addition of an external valve work? Does just adding one valve to the inlet hose work? Will hot water still get to the heater core through the outlet heater hose? Also which hose from the engine side of the firewall is the inlet hose? Any help would be appreciated. Thanks

[BertjeConti]

I think it is a good idea to block coolant going though the heater core with a ball valve om the engine side.