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I feel like the A/C in my 2012 Chrysler Town & Country is under-performing. So, I measured the A/C temperature output on it and my 2003 Toyota Corolla, and I'm having trouble reconciling the results.

Here are the experimental results, based on this setup:

Vehicle        | Outside Condition | Temp Setting   | Fan Setting    | Measured Output Temp
===============|===================|================|================|=====================
Town & Country | 85°F / 55% rh     | Coldest - "LO" | Min ("1" bar)  | 42°F
                                   | Coldest - "LO" | Max ("6" bar)  | 60°F
---------------|-------------------|----------------|----------------|---------------------
Corolla        | 94°F / 35% rh     | Coldest        | Min ("1")      | 45°F
                                   | Coldest        | Max ("4")      | 49°F

(These results show that as the blower speed increases so does the output temperature. This Q&A explains why in lay terms, or see also this technical summary. For a general guide on auto A/C implementation, see this article.)

But why does the Toyota increase 4°F, while the Town & Country increases 18°F? I'd expect a significantly newer vehicle to have the same or better A/C output performance. But no: in the Toyota, one tick more on the blower is one degree up in temperature. In the Chrysler, one blower tick up is four degrees up.

That doesn't make sense to me. Is the A/C on the Chrysler under-performing, and I should spend the cash to have a pro look at it: or is this all just about perception, and I should be happy with it?


Update: Indeed, the A/C was under-performing. The low pressure side was at 20 psi, where nominally it should be around 30 psi. I took it to a pro, who found a failed thermal exhaust valve. Replaced the valve and recharge recycled the refrigerant. Now it blows 48°F at coldest with the blower on maximum. This is inline with the performance from the Corolla.

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    The answer may be in the humidity. It is very energy intensive to condense water. It is also possible that the T&C is low on charge just slightly. I'd suggest to take it to a shop with a RRR (Recover Recycle Recharge) machine that can tell you how much it recovers. Suck down the whole system and see what it pull out then recharge it with exactly what it calls for. Most places will charge an hour or two of labor for that service plus any refrigirant they had to add above what they sucked out. – vini_i Jun 22 '16 at 4:16
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    I have been fascinated with A/C systems in cars of late, and one thing that might very well tell you what's going on is to buy or borrow a set of high and low side pressure gauges. An A/C is all about refrigerant pressure and state changes. Knowing the pressure on the high and low side of your system will tell you a lot, and the gauges are generally under $100 US. Like these: amazon.com/XtremepowerUS-Manifold-Gauge-Diagnostic-Charging/dp/… – cdunn Jun 22 '16 at 16:42
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    If you're in the US it's very likely that your car has R134a refrigerant. I don't know about the rest of the world. That's important that the gauges you get are made for the refigerant used in your car. – cdunn Jun 22 '16 at 16:45
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    @bishop The following Google search produced lots of good results. Way to much information to reproduce here: automotive air conditioning gauge readings Good info here: aircondition.com/tech/questions/82/… – cdunn Jun 22 '16 at 16:59
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    Glad you found your problem. Congrats! That's a great feeling isn't it when you find the solution :) – cdunn Jun 24 '16 at 13:11
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I already commented on an answer to your other question: https://mechanics.stackexchange.com/a/31965/6794

The bottomline is: There's no sense in trying to compare A/C systems in different vehicle types.

If a workshop is out for a quick buck, they will happily evacuate and refill your A/C refrigerant, whether it's needed or not. (I regularly hear the sales persons bluntly lying to customers stating that "the manufacturer recommends this procedure once every two years", while I know that (most?) manufacturers explicitly claim their systems are "maintenance-free".)

Most manufacturers define the A/C as fully functional as long as it maintains low temperatures (<10°C) at the vents on low fan and something like 1500-2000rpm. And it also makes sense this way: A/Cs are controlled via a kind of thermostat which maintains about 0-5°C at the evaporator. If small amounts of refrigerant are lost the thermostat will compensate for that. Only when the refrigerant level is so low that the thermostat cannot maintain those temperatures action is needed; and that's exactly when the air at the vent does not reach those low temperatures mentioned above anymore.

Have an A/C service done as @vini_i suggested for your peace of mind if you want. You may or may not notice an increase in cooling-power afterwards. Judging from your measurements, service is not necessary yet though.

Maybe also note that the A/C system is automatically turned off if a dangerously low level (pressure) of refrigerant is sensed, so that no permanent damage will occur. If that ever happens, you will have no cooling effect anymore and should definitely have the A/C serviced soon.

  • Sorry, I don't buy this. Comparing A/C performance across models absolutely provides guidance for an amateur like me, who wouldn't have otherwise taken the trouble to measure pressure. That pressure read shows 20 psi on low side. That's a problem. Not just a peace of mind problem, but a system leak kind of problem. There is a spectrum between "working perfectly" and "complete failure". The vehicle is somewhere in between those extremes right now, and had I not followed the comparative temperature guidance to investigate further, I'd not have known that until complete failure. – bishop Jun 24 '16 at 13:12
  • Different types have vastly differing AC systems and performance. You wouldn't compare acceleration of an SUV with 200bhp and automatic transmission to that of a sedan with 150bhp and manual transmission, for instance, to check if the SUV has a problem. - As you've read, a slow, continual loss of refrigerant is pretty normal. So if your System has lost e.g. 25% over the years, you wouldn't call that a leak. An existing leak will not cause further damage as long as the system still has enough pressure to not shut down automatically. Hence, no action is required until then. Also, if your syste – JimmyB Jun 25 '16 at 15:47
  • m keeps going "empty" every say 4 years there's no economical justification to try and fix one or more "leaks". – JimmyB Jun 25 '16 at 15:50

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