What temperature should my car’s A/C be blowing out at the vents?
This measurement can be made with an inexpensive thermometer and a manifold pressure gauge set. Evaporator outlet temperature varies according to outside ambient air and humidity conditions. Further variations can be found, depending on wether the system is controlled by a cycling clutch compressor or an evaporator temperature sensor. The design of the hvac plenum ducts is another factor that we need to take into account while running an efficiency performance test.
Refrigerant r134a has roughly a one-to-one temperature pressure relationship, this means for every one-psi increase in pressure; the boiling point increases one degree. Due to this relationship, by controlling pressure, we can control evaporation.
A/C performance testing provides a measure of air-conditioning system operating efficiency. A manifold pressure gauge set connected to the low-side a/c service port and high-side a/c service port is used to determine pressure and a pressure/temperature correlation chart is used as a guide to calculate vents output temperature air.
A thermometer is used to determine air discharge temperature coming out from the duct nozzle into the cabin compartment. On more humid days, operating pressures will be higher on the high side of the a/c system. On less humid days, the operating pressures will read lower on the low side of the a/c system.
Proper auto A/C vents temperature.
In general, with ambient air temperatures 70º degrees Fahrenheit and humidity 20 %, the evaporator outlet air temperature should be in the 35º-40º degrees Fahrenheit range. On the other extreme of 80º degrees Fahrenheit ambient air temperature and 90 % humidity condition, the evaporator air outlet temperature might be in the 45º to 50º degrees Fahrenheit range. That’s a temperature differential of 30º-35º degrees Fahrenheit. Because of all these variations, it is difficult to pinpoint what evaporator outlet air temperature should be on all applications; a good idea is to compare the readings obtained to manufacturer’s specifications.
Car heater core & evaporator core mixed temperature.
The evaporator core and the heater core are very close inside the hvac case separated each other by hvac plenum doors.Hvac case doors with bad seals or failing door actuators could cause the air from the evaporator core to mix with the air from the heater core and impact the temperature of the air coming out from the vents.
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If you think your car’s a/c system is not performing as usual get a technician to check the entire system.