|04-15-2018, 09:11 PM||#1|
Join Date: Jun 2005
2006 VUE 3.5L
Evap temp sensor thermogrease
Like others I've been seeing an issue in which if you drive for several hours the evap eventually freezes up. I went to pick and pull to grab a couple of the temp sensors (since GM doesn't make them anylonger) and noticed that everyone came out dry. The FSM says that the cavity should be packed with the "thermogrease that comes with the sensor". I'm wondering if the sensor isn't reading correctly because the grease is eventually leaking out.
So what grease should I use? Di-electric? Or get CPU sink grease at a computer shop?
BTW: I just scanned mine. In the garage around 75F the BCM shows 1.2v from the sensor. WHen I turned on the A/C it jumped to around 1.9 and seemed to stay there.The FSM doesn't give much clue on how to map voltage to temp but does say that 2.45-2.55v equals 36-38F.
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|04-17-2018, 01:58 AM||#2|
Join Date: Jan 2006
2003 L-Series 3.0L Sedan
Re: Evap temp sensor thermogrease
I don't know if thermistors are the same and if one chart serves as a guide line. ons chart does show an inverse relationship between temperature and voltage. The same for temperature and resistance. The coolant sensor chart may be used here if it helps. What might skew things; different thermistor characteristics and incorrect chart.
With all things considered, baseline values should be kept in mind. Evaporator core temps should never go below approximately 35F otherwise hot and humid conditions at lower temps may freeze condensation, turning the hvac box into a block of ice. Can you confirm your evap coils are freezing? Besides the evap low temperature sensor feeding the control head to prevent continued compressor operation by removing power until evap temps rise above freezing, there's also a matter of loss of refrigerant that can contribute to freezing conditions. While its never been proven of faulty thermal expansion valves causing freezing conditions, other factors can cause freezing/low temperature problems. If you can, measure actual evap coil temps with another temperature sensor - infrared gun, hvac dial thermometer probe, meter and thermistor, whatever. Can your scanner display evap temps?
Everything is considered when lower than normal evap temps cause freezing problems; system contamination with excessive moisture, loss of refrigerant either from a leak or under charge after repair, compressor issues, contamination affecting txv operation and debris blocking liquid flow between condenser coil, filter/drier and orifice tube. Does your system use the orifice tube?
Solid state relays in some equipment use white thermal grease between the rear metal plate on the relays making contact to flat sheet metal to conduct heat away. I've replaced them over the years on drive motors using three phase power. After ten years or so, the grease dries out and becomes semi solid. Scraping it off then applying a glop of new grease makes renewing the heat sink compound some guarantee for long life. A small jar or tube lasts forever.
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