Review on 🌡️ Honeywell C7735A1000 HVAC Discharge Temperature Sensor by Matt Conner

This is easily repaired by hand. I also saved several hundred dollars by avoiding an overpriced call to HVAC service. My problem was that the three thermostats in my 3 year old multi-zone air conditioner needed cold air but the compressor wouldn't turn on. As it turned out, the problem was not a typical failure of the starting capacitor or contactor, as the online specialists explained, but typical problems. (By the way, these parts are also easy to check with a Fluke 117 multimeter or similar and a few simple diagnostic steps. They're also easy to replace yourself if you take the proper precautions when connecting to the mains). In reality there was no 24V signal to turn on the compressor. It turned out that my Honeywell 3 zone controller (HZ311) was blinking the green COOL light instead of always being on, which prevented a 24V ON signal from being sent to the contactor. A quick look at the HZ311 manual provided the answer. The controller thought the channel temp was below 45°F and incorrectly believed the system was overcooled. This temperature was not possible because the compressor was switched off during the day. Remember, systems are designed to shut down if sensors fail before anything irreversible happens. Now I suspected that DATS (Duct Air Temperature Sensor) had failed. I verified this by unplugging a suspect DATS cable from the controller. My compressor kicked on immediately and the air conditioning resumed operation. The compressor later switched off when the target temperature was reached. I ordered this item right away. A few days later when it arrived I installed it and my system continued to work fine. No more wrong 45F degree duct temperature readings. I measured and compared the resistance of the old and replacement sensors and noticed a big difference. The old sensor reported 300 times the resistance of the new sensor. It showed more than 3 megohms.