I don't know where the ETR valve is let alone what is does....I am suggesting that you hook your aux fan directly to a battery and see if it will run first...I checked 8 fans that I have and ony 2 were working...if your fan works then it could be your relay and I can send you a picture of the relay...the relay gets 12 volts from the fuse box and I don't know if it is feeding the other relay like a 123 turbo does...the 123 Aux.fan relay also feeds another relay right next to it on the driver's fenderwell...
I think the monovalve is designed that when it does not work it will stick in the open position and let you have heat all the time...when you are running the AC check and see if the heater hoses going and coming thru the firewall are hot..Jim

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James A. Harris