My '81 380 SLC seems to have a problem with the heat. The heater blows too much heat, as if there is a valve that is stuck open or partially open. I have looked under the hood and found a cluster of heater hoses on the right-rear side of the engine compartment. There is a solenoid/valve that I assume controls the coolant flow. Is there anyway to troubleshoot this valve ? Thanks in advance for all your help.