That might be the case with Landrovers. With my Commodore, there is a valve. There is a valve on the Landrover I have a gas system on (but that isn't climate control).
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The gas converter can still be in series with the heater so long as you use the Commodore style 4 way heater valve. Flow through the circuit is maintained at all times, heater on or off. If you tee the converter before the 4 way valve then the converter gets too little flow when the valve is in the bypass position. Some LRV8's ran a similar valve to isolate the heater, I think it was the 1994 soft dash RRC. I've retrofitted them to some vehicles with worn heater blend flaps.
This is a standard V6 heater valve
https://www.aulro.com/afvb/images/im...15/03/1031.jpg
Heater TAP TO Suit Holden Commodore VN VP VR VS VT VX VY V6 | eBay
This is a standard V8 heater valve
https://www.aulro.com/afvb/images/im...15/03/1032.jpg
Holden VN VP VQ VR VS VT V8 Heater TAP Gates Quality | eBay
Both are on-off valves, neither regulates the flow incrementally. The V6 version allows flow to bypass the heater on full cold setting, the V8 one simply stops it. With the V8 valve you tee in the converter before the valve, with a V6 type you run the converter in series.