The hot tropical climate I call my home necessitates proper cooling from my Car's AC. I have noticed its compressor staying on for approximately 30 seconds then going off for 15 seconds and repeating this cycle. This annoyance has been going on for years and rapid cycling will shorten the service life of the AC compressor clutch. I checked the refrigerant pressures with my handy manifold gauge set during operation of the AC and the pressures are perfect (22psig LOW, 210psig HIGH, 34C ambient, test rpm 1500).
Time to fix the jumbie in my Car's AC! I suspected the temperature sensor in my car to be at fault so read on for how I made a fix. If you live in a temperate or cold climate, please don't do this mod. What I have done is ONLY for hot climates!
Step 1: Locating the Temperature Sensor.
The thermistor responsible for monitoring the temperature is located in the evaporator and in my car that's right behind the glove box.
You can see the thermistor leads going into the evaporator to measure the internal temperature. Measure my arse. It's not doing its job!
I measured its resistance with the car off and it's a 10k thermistor. Luckily I had a spare 10k thermistor. A 10k resistor will be perfect as well.
Step 2: Replacing the Thermistor.
I simply jammed the new thermistor leads into the wire lugs going back to the HVAC control panel. I secured the wires with tie wraps, put the thermistor safe in the wire loom and closed up the glove box.
Step 3: Testing!
I ran the AC during the early morning hours which for us is cold times outside! The aftermarket thermometer I have below my deck registered some cold temperatures. For 15minutes the AC compressor stayed on! Success!
Mind you all of this modification is in preparation for a car automation PC project. The touchscreen windows PC running Flowstone and monitoring via a Labjack u3 hv will make decisions for several car situations. I intend to have automatic cycling of the compressor however not rapid cycling like what the poor compressor had to undergo for these years.
Again if you live in cold climates then do not do this mod. For us scorching sun dwellers, this mod will give you the cooling you deserve and prolong the life of the AC compressor clutch.