I've access to TWO readings at all times:
the head temp sender which reports a relative reading to the instrument panel
the CTS, which informs the PCM, which tells the fans when to turn on and off.
Is the RoadMaster Climate Control relaying
a. [water pump] Coolant Temp Sensor readings
b. [head] Coolant Temp Sender-IP readings
c. (what could 'c' be? Never owned a RoadMaster …)
From the RM sticky I linked above:
Here are the most common you will need to know
-00 PCM diagnostics codes
-01 CCM Diagnostic trouble codes
-02 HVAC Diagnostic trouble codes
-03 SIR Diagnostic trouble codes
-04 ABS/TC Diagnostic trouble codes
-06 Engine RPM
-08 Coolant Temp (°F) - Reading taken at Cylinder head sensor, typically 20* cooler than the -24 reading
-14 Vehicle speed
-24 Coolant Temp (°C) - Reading taken at the Water Pump sensor, This is what the PCM uses to control the fans.
It shows the 2 temp readings - one in F and one in C - so you have apply the formula 9/5 x C + 32 = F to be consistent. Would have made more sense to use the same scale.
So do you have 2 temp gauges, a switching arrangement, or what?
Big thanks to MillerTimeGS for getting me back to reality.