Evaporator temperature sensor

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ptohi
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Evaporator temperature sensor

Postby ptohi » Tue Jul 24, 2018 4:20 pm

One ac system (Saturn) uses scroll compressor, txv and evaporator temperature sensor. My questions are about txv and evap temperature sensor. I don't know if scroll compressors are improvements to vane or pistons. Are txvs redesigned from previous configurations, metering to lower pressures (<28 psi) where freezing occurs and using txv/evap temperature sensor detects this to cycle off the compressor? I was under the belief before evap temp sensors were added, txvs regulated to no lower than 30 psi. I do not recall exact low side pressures, approximately 30-40 psi, on another system (vane type). Am I mistaken?
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bohica2xo
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Re: Evaporator temperature sensor

Postby bohica2xo » Sun Jul 29, 2018 2:48 pm

Moved topic to proper forum.

The answer would depend on the year & model of Saturn. Tell us more.
ptohi
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Re: Evaporator temperature sensor

Postby ptohi » Sun Jul 29, 2018 6:55 pm

Thanks for moving the thread. This isn't my vehicle but enquiring about the differences between Saturns with and w/o evap temperature sensors. '06 Saturn Vue, auto climate control, scroll compressor, evap temperature sensor. Saturn Vues seem to have scroll control valve issues similar to Ford is having with most control valves replaced to restore ac function. I'm a Saturn forum member but not a Vue owner. The question, does the evap temperature sensor allow fine tuning evap pressures for colder air closer to freezing over previous systems without this sensor? My '03 L300, repaired and back to factory condition still shows center vent temps at 42F in hot and humid weather (85-95F) at speed.
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bohica2xo
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Re: Evaporator temperature sensor

Postby bohica2xo » Sun Jul 29, 2018 7:57 pm

The Vue used a temp sensor in the suction line at the TXV. This was smart, because under high heat load when the gas leaving the evaporator was above freezing, the core could be slightly below that temp to provide better cooldown under high heat loads. A sensor stuck in the middle of the evaporator takes an average.

There is a TSB for the thermo switch installation on the 2005-2007 Vue. The switch sits in a well, and it is isolated from the refrigerant. It can be changed without discharging the system. The TSB relates to a condition where there was not enough thermal transfer grease placed in the well the sensor sits in. This condition keeps the switch from responding accurately. The fix is simple, pull the switch & add some heat sink grease.

The Vue was a decent car with the Honda 3.5L V6. Too bad about Saturn
ptohi
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Re: Evaporator temperature sensor

Postby ptohi » Mon Jul 30, 2018 9:41 am

Thank you for the education and heads up about a service bulletin to use more thermal grease. A few members are having issues and the temperature sensor is suspect (thermal grease was mentioned).
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bohica2xo
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Re: Evaporator temperature sensor

Postby bohica2xo » Mon Jul 30, 2018 1:26 pm

Remember that Thermal Grease is not regular grease, or dielectric grease.

Use good heat sink grease, like Dow Corning 340, Arctic Silver, Ceramique 2 etc, The same stuff you would use on a CPU heatsink.
Ceramique 2 seems to work very well, and it is not expensive. Be sure to clean the well & sensor to remove any old grease before starting over - anything left in there is 10 years old.

My wife's 2007 Vue had about half of what it should have in that cavity when I checked it - in 2007. I think many of them were under-greased.

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