Last weekend it was 72 degrees and sunny in Texas! I took my Series III roadster out and she drove great until I noticed the temperature increasing. I suspected and confirmed the cooling fans were off and suspected a blown fuze. When I got home and opened the bonnet, I found a burned fuze holder on the frame rail that controlled the fan circuit. Obviously, something is drawing way too much current! I have dug into it and found one of the aftermarket fans the PO installed, no markings other than a 12V sticker and a 10 and 95 stenciled on them, had died. I will be looking at replacement fans and trying to match what the PO installed. I replaced the burned fuze with a resettable circuit breaker.
In diagnosing the issue, I have noticed when I turn on the air conditioner, the remaining good fan no longer comes on. I know it works as I can get it to spin when I apply 12V to it and can get voltage to the harness connectors when I bypas the thermal sensor I installed to replace the otter switch. I suspect the issue is the AC relay that is a 3-terminal 6RA relay (part number C18122 in the parts manual or SRB111 in the SNG catalog). No matter, while I have the radiator cover off, I want to replace both relays.
The fan relay (C31791) is easily available and looks the same as mine. The AC relay, C18122, has 3 connectors on my car but all the replacements seem to have 4 terminals. I appears the 3 terminal variety are no longer available. Does anyone know what has to be done to wire the newer 4 terminal relays to make them work?