Multiplexer causing data corruption?????

Hey all, I’m really stumped.

I’ve been trying to make a temperature sensor to put in my refrigerator. I’m using a TMP36 temp sensor, sending data to an Adafruit Feather Huzzah 8266 and thru that to AdafruitIO. Since I also want to monitor battery voltage and the Huzzah only has one ADC, I’ve added the SparkFun Multiplexer Breakout - 8 Channel (74HC4051) to send alternately the battery voltage and the temperature voltage.

I’ve managed to get it working with only the TMP36 and no MUX, but when I add the MUX, the temperature voltage no longer drops when I put it in the fridge. Since it works without the MUX, it seems to point to the MUX as the problem, but I can’t think of why that would be. When I try it with the multiplexer, I DO get realistic values from the battery voltage, but not the temperature.

Can anyone suggest what is wrong?

Are you sure you’ve selected the correct port on the MUX? If the temp isn’t changing at all, I’d suspect your selecting the wrong port on the MUX.