Why are car a/c systems so prone to breaking?

ISTM that the a/c system is perhaps the part of the car most prone to needing repairs. And if you compare a/c in cars to a/c in houses, or even mobile units, the car systems are far more likely to need repairs. In particular, refrigerant leaks, but even other parts going as well. Why is this?

The only thing I can think of is that a/c units in buildings are stationary, while those in cars are constantly getting bounced around on the road. But I don’t know if that accounts for it.

That’s part of it. The other part is that the A/C on a car needs a lot of power, and for conventional IC-engined cars with a 12-volt electrical system, the only reasonable way to deliver that much power is with a belt-driven shaft. That means there’s a mechanical seal on the shaft that’s subject to wear. A hydraulic system will generally only leak when it’s operating (because that’s when there’s pressure), but an A/C system is pressurized even when it’s not running. So once that shaft seal starts leaking, it’ll leak 24/7 until the refrigerant is gone. Add in all the other issues for cars - vibration, weight constraints that limit how durable you can make something, etc. - and it’s maybe not so terribly surprising that leaks happen.

In comparison, stationary A/C units and refrigerators/freezers don’t have any mechanical shafts penetrating them. Power is delivered via electrical wires to an electric motor that drives the compressor, and the electric motor and compressor are sealed inside the low-pressure side of the system. With no moving shaft seals that can wear out and cause leaks, and none of the vibration that you see on a vehicle, yes, stationary A/C units and fridges/freezers tend to be more trouble-free. Eventually you’ll get microcracks in the evaporator, but that can take years.

I’ll confess I don’t know much about the A/C systems on battery electric vehicles. But since they have high voltage available, an electrically driven compressor is much more feasible than on a conventional car with a 12-volt system, so ISTM you could eliminate the shaft seal problem and have a fully sealed system like a stationary A/C system.

I haven’t had any problems with car A/Cs except after many years they may need a refrigerant recharge. Seems to me other types of car repairs are more common.

I have had the same experience. The only time I had a real problem was after an accident when the compressor was damaged.

We had a mysterious problem with my wife’s Forester. The A/C would disengage early when it got hot in the engine compartment, like it especially does in summer time. When A/C is used. So we got only a few seconds of A/C.

Two different shops (not Subaru specialists) could either not recreate the problem or they tried to bandaid it by just topping off the refrigerant and checking for leaks (not found).

After 3-4 years, I encountered a video on YT from a Subaru guy describing a “common problem” with Subaru A/C’s, that they sometimes disengaged early, because their magnetic clutch was wearing out. (The metal clutch surfaces were wearing, so the gap closed by the electromagnet was too large to close the clutch when energized.)

Actually I saw two different videos saying this. The non-Subaru guy recommended not trying to fix the clutch as it was really hard to get off. The Subaru guy showed how to do it relatively easily. I followed that method and removed a 1/3 mm shim. It seems that Subaru anticipated this issue and acted accordingly. Anyway, this shim removal actually resolved this issue. With the clutch gap decreased, the magnet could now do its job.

Yes, A/C units in a car are complex and even present mechanics with “stumpers” in my experience.

AFAIK, all replacement compressor clutches come with a variety of shims. The space between the clutch body and the clutch plate is supposed to be adjusted with the shims to meet spec.

Yeah…I was starting to suspect this. Which made my two mechanics’ failure to even suggest this fix even more annoying.

FWIW, the fix cost me less than $5 in parts, just a few metric bolts to gently tighten (the clutch even had holes just for these!) to pry off the clutch from the shaft.

Leaks are more likely in car A/C systems because everything is being physically stressed and jostled from driving. Each wiggle of a pipe is another opportunity for gas to escape and connectors to get looser.

One thing people may not realize is that a car A/C is pretty hefty. Typically it’s about 12,000 BTUs, which would be the equivalent of an A/C used for a 600 sq ft space. But with space in a car being a premium, they have to make it as compact as possible. This can also affect reliability. But overall, car A/C systems are relatively reliable considering all they are put through.

I don’t get the comments implying that refrigerant recharge is not a repair. Refrigerant doesn’t get used up. If it needs to be recharged, that means that there’s a leak somewhere.

What I came in to say. An unscrupulous mechanic will tell you that it needs to be recharged periodically, but that’s bullshit for a closed system. If it was actually true, you would need to periodically recharge your refrigerator. Also, if your car AC is providing cold air, a mechanic does not need to slap gauges on it to “check the system” and then charge you for the service.

Your refrigerator is not subject to the same kind of stresses, and is built very much differently than a car AC. If you are getting leaks in your refrigerator, you are using it entirely wrong.

An AC unit can be providing cold air, and still be low on refrigerant.

It means that it is operating inefficiently, and will soon stop operating altogether, but it will still be blowing cold air. In fact, as the pressure in the system decreases, the output air will actually get colder.

This. When a system is running low on refrigerant, if there’s plenty of environmental humidity then the usual condensation on the evaporator coil becomes ice and can completely block the air flow through it. If your A/C is on, and the blower is turning, but you don’t feel any air coming out of the vents, this is the likely cause (and it can be temporarily remedied by turning the A/C off but keeping the blower running).

That’s amazing. My old window unit (it came with the house I bought 12 years ago and was probably 20+ then, it had a fake wood grain front panel) and replaced it with a 12k which cools my entire small place.

You may have missed my point.

I’ve never had an AC problem, but I get rid of my cars after 5 or 6 years. Maybe they didn’t have enough time to break.

But a car A/C is an imperfectly closed system due to the seal around the mechanical shaft driving the compressor. Aside from all the bumping and jostling around, cars are also subject to huge temperature swings, which can wreak havoc on joints, seals, and fittings. I had a VW Passat that needed the A/C recharged every spring for a couple years (it would blow cool-ish but not cold, though they never could find a leak), but then one spring it didn’t, and for the last two or three years I had it the A/C worked fine. So the leak managed to plug itself. That can sometimes happen when you have rubber-like seals and gaskets. On a home/office A/C a poorly-seated schrader valve can leak out the whole charge, but a little jostle or opening/closing it can get it to seat properly and hold for years.

At least on residential systems, if the suction line going back into the condenser unit is cold and sweating, then the charge is probably ok. However if it’s frosted then it’s low on charge, and if it’s room temperature then it’s very low on charge. An A/C can still function OK with a low charge, especially if it’s not too hot out, but once the charge drops below a certain point then it falls off a cliff. Basically it’s not a linear relationship, to such a degree that 1/3 empty or maybe even only 1/3 full will still work, but beyond that it’s done.

Same here. I don’t like making payments, but I like a vehicle that’s dependable

I must have. The point that I took from your post was that it is an unscrupulous mechanic that would tell you it needs recharged, and then you compared it to a refrigerator as though they had similarities.

If you were not saying that a refrigerator is like a car AC, then what point were you making?

Didn’t mean to create a controversy. I’ll concede that some of my remarks are incorrect and let’s move on.

I keep my cars until they get around 250,000 miles. That takes a few years. Never had a car AC fail me yet. I don’t see the AC system as a weak part of the car.