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YOUR RESEARCHAC airflow slows down after 20 minutes
Leading reported evidence
Fill slightly or even more than slightly depending
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It can end up overfilled or under-filled slightly or even more than slightly depending on how good the guess is.
Leading evidence: 'Fill slightly or even more than slightly depending' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Fill slightly or even more than slightly depending' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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By this June when I got it back, it didn't work at all.
My AC blows cold, but after about 20 minutes I notice the airflow through the vents is much reduced, even if I manually have only the face-level vents open.
Running it with the compressor off for a minute or two restores full airflow for another ~20 minutes.
Anyone recognize this strange symptom? I thought maybe the evaporator is icing, but then I would expect the ice to take longer to melt than two minutes if that was the case. Any way I can confirm or disconfirm ice? What else might it be?
Many thanks in advance.
Sounds like icing but i have no experience with car AC icing so who knows. I would expect 1-2 minutes would melt the ice. Look under the car, does a bunch of water drip out during the 1-2 minutes?
It's supposed to do that, it is climate control. As the computer senses that the temperature is reducing it will regulate the airflow. I guess when you turn it off the temperature rises again hence full airflow
Are you running it on AUTO? As the interior cools the fan is regulated. That's the way it works. If you want full cool, just hit the STAR button and regulate the fan yourself.
It could be icing the compressor freezing up..forgive my lack of technical experience. It happens on occasion to my wife’s SUV and it’s happened in previous cars I have owned over the years. It works fine...then the flow diminishes...you turn off the AC for several minutes...it goes back to working normally.
As others have mentioned it sounds like the evaporator inside the dash is icing over. If the Freon is low, the evaporator temp will be below freezing and the moisture on the evaporator will freeze over and build up untill it starts to block off air flow through the evaporator. Turning off the A/C allows the ice to melt, restoring air flow, then the cycle repeats. You need to have the system recovered, evacuated and recharged with proper amount of Freon.
Thanks for the comments everyone.
To be clear, what I am describing is not the normal modulation of the fan speed. When I’m talking about happens even if I manually hold of the fan at a fixed speed setting.
@Porschetech3
Is it necessary to evacuate? Why can’t I just top it off?
My AC recently "quit"... I had topped off the 134a last summer (before sending it away for the engine rebuild), as the AC didn't seem to be getting as cold as it used to - seemed to work a little better, but still didn't get as cold as it used to. By this June when I got it back, it didn't work at all. I checked all the obvious stuff and couldn't find anything wrong or out of place (all wires plugged in, freon seemed to be full, etc.). I broke down and brought it to a shop with an AC vacuum system. They evacuated the system and re-charged, pressure tested etc. All back to normal! Definitely worth the $300 it cost me (I wish I could have done it 2 or 3 weeks ago when we had our heat wave...).
It's not absolutely necessary, but just topping off is really an educated guess. It can end up overfilled or under-filled slightly or even more than slightly depending on how good the guess is.
For top performance, the system is recovered (Freon amount weighed/measured) , system evacuated, then Freon that was recovered is recharged into the system along the needed amount to be full charge. This is the only way to guaranty an accurate full charge.
