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Just had my compressor, condenser and dryer replaced, all OEM parts. The shop supposedly flushed the system and replaced the little micro filters.
While driving home on surface streets I had the air on with the fan at 3/4 speed.
I Have one of those round temp gauges with the long pointed rod, like a cooking thermometer in the center dash vent adjacent to the instrument cluster.. It’s a common type that a/c guys use.
While driving home the temperature variation was 42-48 degrees. It seemed at idle it wasn’t as cold as driving. Outside temperature was about 63 degrees.
is it normal for the temperature to vary like that?
Typical,
you are getting too picky. if the Vent Air is below 50*F it is doing a good job when the outside Humidity is 50% or more, right now, as you can see below, it is 96% Humidity outside. Our car/truck AC will NOT get cold very fast, in those conditions if you are on Outside Air, or using Defrost.
you want it to stay at 38*F all the time, and the world is just not that way.
Humidity is just about the greatest thing there is to preventing AC from getting as cold as you want.
you can't use Outside Air, and expect to get Cold Air at low RPMs, the Fan needs to suck tons of air thru the Condenser.
IF on Recirculate, the interior Humidity must be dropped down below 40% to get that nice, Ice Cold feeling.
Here is a Perfect example, this is my Home thermostat, it is on the Internet so I can access it from anywhere.
on my '01 K1500 Suburban, when we were returning from South Dakota in 103*F temps, the AC Vent was so cold, the Dogs in the back were curled up with their nose in their tails.... and up front, we were backing the Temp back up... but it took at least 2 hours to drop the interior down that low.
My question is primarily if it’s normal that the temperature going through the vent varies from 42-48 degrees. I realize in a day that’s 63 degrees is not a good test for an a/c system, but it is winter time here in SoCal and I have no other way to test the system until the weather changes and it warms up.
my guess is that it’s perfectly normal for the vent temperature to vary a few degrees for the reasons you explained.
Btw, yes I am picky. When I pay hard earned cash for OEM parts and service for the system, I expect it to operate like new.
yes,
mine swings that much,
I don't have the Thermo meter in the vent anymore,
kept looking at it, instead of the road
Yeah, not only am I fixated on that but I have three other gauges above the rear view mirror and a Garmin GPS to the left. My head spins a lot of the time. lol
There are several variables here. The most obvious would be at idle the compressor is not pumping or moving the volume of refrigerant as when above idle. This creates a variance in the final temp as the evaporator is fed less Freon or volume. This is where the Temperature/Pressure charts are used. The relation of Freon and it's temp produce a known pressure. In thermal dynamics it is taught that "There is no such thing as cold, It's lack of heat". When we cool something it's simply the removal of heat (occurring at the evaporator) and we are left with cold. Air entering the evap that is essentially cooler, contains less heat, and therefore system discharge temps may be hard to properly evaluate, but an accurate measurement would be the temp pressure chart, requiring gauges to be installed on the service ports. Provided the system internals are clean, the proper amount of oil was added ans the mechanical health of the system is good, you can rely on the temp pressure chart to inform of proper charge and system function. Beyond that you get what you get from the design of the system, such as it's designed ability to absorb the heat in the evaporator, or (Superheat).
01__Excursion certainly knows his stuff. AC performance varying with RPMs is expected. The serpentine belt spins slower at lower RPMs, therefore the AC compressor is not running as quickly either. I have also anecdotally noticed my AC performance take a dip at idle as well. Also with the vehicle at stand still there is no air rushing over, around, and through the engine bay, and we KNOW how much heat these 7.3s put off! This makes it harder for the electric AC fan to pull in cool (ish) air. Finally, I believe these AC systems are limited by their 20+ year old technologies and efficiencies. If only you could tune your AC!
Thanks for the enlightenment gentlemen. Certainly I noticed and could measure a difference from the dash vent so I’m confident that the new components are an improvement over the original 25 year old compressor, condenser and dryer. The hoses were replaced about 2 years ago and if the shop did the job right, they replaced the two micro filters (I forgot their proper names), and flushed the system properly. According to the work order they charged it wit 4.25 lbs of refrigerant.
I just want the best a/c system I can get given the limitations of the design.
Our rainy season has just started here in SoCal so I’ll just have to wait for April or May when it warms up to know for sure.
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