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In principle, Roger, there should be two ‘thermostats’ involved; one relating to cabin temp/air flow temp. On the SI with plain heating, this is the ‘heater sensing unit’ which varies flow through the water flow through the heater core. This ‘thermostat’ is varies vacuum applied to the heater valve and heater flap actuator - basically using ambient air to cool and heater to warm according to driver’s ventilation control settings to automatically control cabin temps…
On the Del II an in-car sensor detects cabin temp and an electronic AC amplifier translate various sensor data to control flaps, heater and fans via a servo. The question on your system is whether such ‘automatic’ controls are used to stabilize cabin temps - and if these are involved in the change of outlet valve temps…?
The Ranco is just a switch, connecting and disconnecting compressor to prevent that the evaporator from freezing up. The main temp control, ‘thermostat’, for maximum cooling effect. of the evaporator is the expansion valve, varying refrigerant flow into the evaporator based on outlet pipe temp and inlet pipe temp - to ensure that the correct amount of refrigerant is injected into the evaporator. All refrigerant must be evaporated, with no liquid residue
This ensures that the evaporator is kept as cold as possible - the maximum cooling effect. If the outlet pipe temp increases, the expansion valve increases refrigerant flow - and vice versa, to ensure the evaporator stays the coldest possible/allowable. All the while; the evaporator is affected by the air flow through it - but if the ambient air temp is too low to keep the evaporator above 2C even with the regulating effect of the expansion valve - the Ranco turns off the compressor.
In effect; the Ranco, working properly, has no influence on actual evaporator temp variation. If the Ranco turns off the compressor prematurely; it is faulty - but even then; the evaporator does not operate continuously at the limit of 2C, it is likely ‘warmer’ than that. Ie, air outlet temps is not necessarily tied to Ranco controls - and the cooling capacity of the evaporator is not infinite. If ambient air is hot enough; even optimum delivery of refrigerant may not prevent its temps to rise. And also; the faster the air is flowing through the evaporator the less the outlet air is cooled - and as the ambient airflow itself always heats the evaporator, the feedback effect will influence outlet air flow temps…
In theory; checking evaporator temps versus air outlet temps is one way to clarify mutual effects. And indeed to verify, by watching compressor engagement/disengagement clarifying if the Ranco is functioning as it should. A somewhat risky test is to bypass the Ranco, to see how this affects air outlet temps. However, this may cause destructive icing and may not be conclusive…
Adding further Insulation around the evaporator (and heater) to reduce outside interference is fair enough - but probably has minimal effects, given the overall system capacity…?
Much depends on the configuration of the various controls on your AC system - to eliminate possible factors other than the ones mentioned…
But again, if the system gives satisfactory cabin temps; drastic actions seems like a bit of overkill…?
Frank
xj6 85 Sov Europe (UK/NZ)
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