Is my TDS meter working?

[mike31154]

I also get 0 TDS out of the RO after running for about 4 gallons of product water, but that's only in the winter time when the water temperature going in to my system is below 10 Celsius. I stuck one of those cheap strip thermometers on to the first stage cartridge housing. Best I can get in the summer is 1 TDS out of the RO. That's also why I tend to make at least 5 gallons of RO water before switching over to making DI.