What is your protocol for testing A/C vent temperature?

[brages]

Yeah, I know -- just drive the car and if you're miserable, there's a problem.

It's easy to fool yourself, though. If you are wanting to take a more "scientific" approach, how do you eliminate as many variables as possible? Fan on high, full cool... recirc on or off, windows open, etc. Rear a/c on or off? What engine RPM? Bring the engine up to temp first? What is your target number? 30 deg F below ambient at the center vent?

 

[pbm]

I've always found that my A/C was coldest (according to a thermometer placed in the vent) on lower fan settings. This has been true in every car I've checked. I'm not talking a lot but say 42*F on low vs. 44 or 45*F on high.
I never measured it against the outside temperature but 45* F or lower at the vent is my goal.

 

[zrxkawboy]

There is usually a procedure in the service manual that specifies settings, etc.

 

[Luftmasse]

For me personally, if it can handle a minimum of 60% of the outside temperature, it is adequate enough.

 

[kschachn]

There is usually a procedure in the service manual that specifies settings, etc.

Yes this.

 

[brages]

I've always found that my A/C was coldest (according to a thermometer placed in the vent) on lower fan settings. This has been true in every car I've checked. I'm not talking a lot but say 42*F on low vs. 44 or 45*F on high.
I never measured it against the outside temperature but 45* F or lower at the vent is my goal.

Right, fan speed is one of the variables.

There is usually a procedure in the service manual that specifies settings, etc.

I am a Youtube Certified mechanic; I don't have any service manuals. What does a typical official procedure look like?

For me personally, if it can handle a minimum of 60% of the outside temperature, it is adequate enough.

in Kelvin?

 

[brages]

Found this procedure for Honda Civics: http://www.pontiacpower.org/pdf/ACtestUS.pdf

1500 rpm, hood and doors open. Max A/C (recirc) on. Run for 10 minutes. Looking for 30 degree F drop from ambient, plus or minus a bit based on humidity.

 

[kschachn]

Yeah, here are a couple relevant pages out of the manual for my old Honda.

 

[Chris142]

I evacuate the system, vacuum and charge to factory spec . Once that's done I move on to any diagnostics I need to do.

 

[Kestas]

I thought it was advisable to spritz water on the condenser in front... probably to reduce head pressures in the a/c.

 

[SHOZ]

I have one in my vents all the time. When everything settles down it will bounce off the evap temp sensor, 37F-40F with low fan speed and recic. When hot after about 5 minutes of the compressor running it will blow nearly 40F with the fan on high in recirc but not cycle. System pressure triggering the radiator fan at speed though.

 

[GMBoy]

I evacuate the system, vacuum and charge to factory spec . Once that's done I move on to any diagnostics I need to do.

This is exactly what I do with every vehicle. The only way to know if you are at the proper charge is to recharge it. Usually most vehicles coming in for ac issues the owner has already tried adding freon and now we don't know where its at and diagnosing properly relies on correct charge. Excellent point.

 

[Nick1994]

30 degrees below ambient temperature would be absolutely miserable.

 

[kschachn]

30 degrees below ambient temperature would be absolutely miserable.

Do you ever operate your A/C other than in recirculate?

 

[someonesomewhere]

Found this procedure for Honda Civics: http://www.pontiacpower.org/pdf/ACtestUS.pdf

1500 rpm, hood and doors open. Max A/C (recirc) on. Run for 10 minutes. Looking for 30 degree F drop from ambient, plus or minus a bit based on humidity.

This is the procedure we used at the shop I worked at, and we were certified. Been almost 20 years ago though. Maybe different now for some, idk.

 

[John105]

Yeah, I know -- just drive the car and if you're miserable, there's a problem.

It's easy to fool yourself, though. If you are wanting to take a more "scientific" approach, how do you eliminate as many variables as possible? Fan on high, full cool... recirc on or off, windows open, etc. Rear a/c on or off? What engine RPM? Bring the engine up to temp first? What is your target number? 30 deg F below ambient at the center vent?

I actually used what I had, a digital meat thermometer.

With my wife’s GM suv, I could not get low40s as I saw some cars on YouTube. 49-50 at best.

Achieves lowest temp with sustained 2000 rpm+…

 

[E150GT]

Yeah, I know -- just drive the car and if you're miserable, there's a problem.

It's easy to fool yourself, though. If you are wanting to take a more "scientific" approach, how do you eliminate as many variables as possible? Fan on high, full cool... recirc on or off, windows open, etc. Rear a/c on or off? What engine RPM? Bring the engine up to temp first? What is your target number? 30 deg F below ambient at the center vent?

Windows closed. Fan speed low. Recirc on. Condenser fan working. Should look for 38 to 42 at the center vent. If you have that then you are good to go. If not, then you can start looking into things

 

[PontiacHO]

Do you ever operate your A/C other than in recirculate?

Yes. When you’ve first started the AC system in a heat/sun soaked/baked car. The outside air temp is most often cooler. 90 outside vs 120 inside. If you can get moving quickly rolling the windows down and flushing that hot air out works better though. Then switch to recirculating air.

 

[John105]

Also ambient temp matters. In my case it was 90F. If I’m not mistaken getting below 40F is when the ambient temp is mild like 70F

 

[Nick1994]

Do you ever operate your A/C other than in recirculate?

When getting in the car I roll all the windows down for 30 seconds or so and set the A/C to outside air. Roll the windows up except I leave one rear one cracked an inch or two. This lets it push all the hot air out of the car. Once I get a reasonable temperature in the car I’ll roll the window up and use recirculate.

But when the car has sat in the sun, all of the dash plastic is insanely hot so recirculating is hard initially.