Air Conditioning - what temperature differential?
Discussion
What temperature differential would you expect to see on a car Air Conditioning system? if I put a thermometer outside the car, and one in front of the air vent with the air con fully on, engine revs at say 2000 RPM so the system is working fully, what temperature difference would you expect to see?
Debaser said:
Not sure I really understand the question, but the thermometer outside the car (in the shade) will show the outside temperature, and the thermometer in front of the vent will show a fair few degrees colder than whatever temperature you've set the AC at.
Good point, thermometer outside in the shade... this assumes Air Con not climate control so no regulation of the temperature by the climate sensor.the question is, how many are a "fair few degrees"!
WTF ?In general I'd expect this sort of differential:
a) Outside temp reading on car thermometer.
b) Inside aircon temp set by user.
Delta T = a - b
ETA, oh wait. The above assumes it's hot outside and you want it colder inside. Of course you could make Delta T = b - a
Also the above assumes that the aircon actually reaches the temperature set on the unit, oh, and that the outside thermometer reads the outside temperature acurately
Edited by Fatman2 on Thursday 18th November 23:26
I think the OP is asking:
If you were to park your car in the shade with a air temperature of say 25 deg. C, then when the A/C was turned fully on what is the temp. difference between ambient and vent air, hence how much should the aircon cool air by.
Edit:- I think the OP is asking if anyone has done this test - perhaps to see if his A/C is functioning properly?
It would be different for different cars and depend on the ambient temperature, condition of the system etc. (don't have A/C so can't try it...)
If you were to park your car in the shade with a air temperature of say 25 deg. C, then when the A/C was turned fully on what is the temp. difference between ambient and vent air, hence how much should the aircon cool air by.
Edit:- I think the OP is asking if anyone has done this test - perhaps to see if his A/C is functioning properly?
It would be different for different cars and depend on the ambient temperature, condition of the system etc. (don't have A/C so can't try it...)
Edited by Colin 1985 on Thursday 18th November 23:26
Fatman2 said:
WTF ?In general I'd expect this sort of differential:
a) Outside temp reading on car thermometer.
b) Inside aircon temp set by user.
Delta T = a - b
At the moment a bit of googling seems to suggest between 17 to 22 degrees F
buzzer said:
Debaser said:
Not sure I really understand the question, but the thermometer outside the car (in the shade) will show the outside temperature, and the thermometer in front of the vent will show a fair few degrees colder than whatever temperature you've set the AC at.
Good point, thermometer outside in the shade... this assumes Air Con not climate control so no regulation of the temperature by the climate sensor.the question is, how many are a "fair few degrees"!
It really depends on the interior temperature of the car (as the interior cools the vent outlet temperature will increase).
Any HVAC engineers feel free to correct my numbers!
a bit more googling found...
"The temperature drop across the coil is dependent on the relative humidity of the air, the wet bulb reading of the R/A, and the ambient temperature of the car. But a good rule of thumb is in between 17 and 22 degrees Fahrenheit."
kind of answers my question but if there are any air con engineers on here I would like to hear real world examples.
"The temperature drop across the coil is dependent on the relative humidity of the air, the wet bulb reading of the R/A, and the ambient temperature of the car. But a good rule of thumb is in between 17 and 22 degrees Fahrenheit."
kind of answers my question but if there are any air con engineers on here I would like to hear real world examples.
^^ Sorry I was just being facetious.
I'm sure it varies between manufacturer but will likely be at fridge temperatures i.e. 17 degrees. Naturally this will be difficult to actually achieve in a car on a hot sunny day (due to all the glass) but will be passing through the vents at this kind of temp.
I'm sure it varies between manufacturer but will likely be at fridge temperatures i.e. 17 degrees. Naturally this will be difficult to actually achieve in a car on a hot sunny day (due to all the glass) but will be passing through the vents at this kind of temp.
Debaser said:
buzzer said:
Debaser said:
Not sure I really understand the question, but the thermometer outside the car (in the shade) will show the outside temperature, and the thermometer in front of the vent will show a fair few degrees colder than whatever temperature you've set the AC at.
Good point, thermometer outside in the shade... this assumes Air Con not climate control so no regulation of the temperature by the climate sensor.the question is, how many are a "fair few degrees"!
It really depends on the interior temperature of the car (as the interior cools the vent outlet temperature will increase).
Any HVAC engineers feel free to correct my numbers!
My old Corolla has air con. there is no temperature regulation, the Air Con is on... or off.
Ignore climate control for the moment. If you put the air con on in a car and set the heater to recirculate, in theory the car should get colder and colder as the air con unit removes more and more heat from the air.
Edited by buzzer on Thursday 18th November 23:42
buzzer said:
This is where its getting confusing! my Audi TT has climate control. I can set the temperature I want in the car on a digital display. the system keeps the car at the set temperature. that's Climate Control.
My old Corolla has air con. there is no temperature regulation, the Air Con is on... or off.
Ignore climate control for the moment. If you put the air con on in a car and set the heater to recirculate, in theory the car should get colder and colder as the air con unit removes more and more heat from the air.
Initially the auto AC will be at maximum cooldown so the numbers will be the same as manual AC. Obviously the manual AC won't increase the vent outlet temp as the car cools so if you leave it on 'cold' with a high fan speed you'll just keep cooling the interior of the car. Evantually you'll get to a balance where the interior is being cooled by the AC as much as it's being heated by sun load.My old Corolla has air con. there is no temperature regulation, the Air Con is on... or off.
Ignore climate control for the moment. If you put the air con on in a car and set the heater to recirculate, in theory the car should get colder and colder as the air con unit removes more and more heat from the air.
Edited by buzzer on Thursday 18th November 23:42
If it's hot outside and your car hasn't got a good AC system the interior might never get cooler than 25C. On a cold day and with a good AC system you'll get it a lot cooler.
A proper HVAC engineer would be able to give you better numbers (some AC systems don't put out cold air when the ambient is below a certain value) - I don't really work with HVAC.
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