Car AC theory question

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I am sure if the paint had any negative effect on function the people building hem would not paint them.
Harry K
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I would also think that one of the functions of the paint is to protect the aluminum from the elements, like road salt. If painting them made any significant difference in performance, then they would also paint other aluminum condensers, like home central AC units. I haven't seen one of them with paint......
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On 3/13/2013 7:32 AM, snipped-for-privacy@optonline.net wrote:

Do you drive your house through a salt water and sand slurry on a regular basis?
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Andrew Muzi
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minum

Wooosh...... You might want to read what I posted and the context of the thread again...
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On 3/13/2013 12:41 PM, snipped-for-privacy@optonline.net wrote:

You're right. sorry.
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Andrew Muzi
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On 03/12/2013 09:40 PM, Harry K wrote:

what some people believe to be true and what is actually true aren't the same thing. most small shops run on artisanal tradition, not science - they may believe there's no negative impact of doing something, but i doubt any but a very few have ever actually tested.
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fact check required

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I don't think he's necessarily speaking of small shops. What about all the radiators being built by major manufacturers, for the auto companies, to the auto companies specs?

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Basic summary:
1. The black coating improves heat loss by radiation. But, since very little of the actual heat loss from the condenser is by radiation (most is from convection), it doesn't really make much of a difference.
2. Putting a layer of something on the outside of the aluminum will indeed reduce heat transfer a little if that something is a poorer heat conductor than aluminum.... but indeed since a layer of paint is thin it doesn't really make much of a difference.
If I were making condensers, I would do black anodizing. You get a nice black surface, you don't get much change in heat transfer since there really is no coating, and you get something nice and hard that is much more resistant to corrosion.
And that's really the main issue... corrosion builds up and both provides an insulating layer and eventually eats the fins away until you don't have as much surface area anymore. --scott
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"C'est un Nagra. C'est suisse, et tres, tres precis."

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Ashton Crusher wrote:

The R-Value of a layer of paint, virtually any paint, is too small to measure.
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On Tuesday, March 12, 2013 7:38:38 PM UTC-4, Ashton Crusher wrote:

I've always wondered why it costs $1,200 to fix a car AC but you can buy a room AC to cool a room with the volume of a dozen cars for $100.
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a room AC to cool a room with the volume of a dozen cars for $100.- Hide qu oted text -

For the same reason that it could cost several hundred to fix that room AC, if it failed. And the fact that the components of an auto AC are usually not very accessible. The evaporator for example, is buried in the dash. You can't just take off a couple pieces of outer sheetmetal off and get to everything right in front of you.... With labor rates at $100, what do you expect?
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wrote:

$1200 is if it's an easy job. I've heard of several that were nearly $2000. My Brotherinlaw's Volvo needed $2000 in repairs and a year later it broke again and they wanted another $2000 to fix it. He did as they hoped, he bought a new car.
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On Wednesday, March 13, 2013 10:47:54 PM UTC-4, Pavel314 wrote:

IIRC it takes 3 tons to cool a car, same as it does for my whole house.
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On 03/13/2013 09:47 PM, Pavel314 wrote: <snip>

I've recently been wondering the same thing. I can accept that under-the-hood is a hostile environment, but the disparity in price seems too large.
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y a room AC to cool a room with the volume of a dozen cars for $100.

First, it doesn't always cost $1,200 to fix a car AC. If it's a bad switch or a corroded wire to the compressor it could be $100. If it's leaking shrader valves, it could be $250. Second, you're comparing the cost to repair something with the price of a new cheap, mass market appliance built on a high volume assembly line. If that $100 air conditioner had a compressor that failed, shred metal bits, contaminating the whole thing, what do you think it would cost to diagnose it, take it all apart, flush it, purge it, braze in a new compressor, recharge, test it, etc? It would be many times the $100 it costs for it to begin with, so it just isn't done. You can't throw away the auto AC as a unit and get a new one, so you have to deal with what's there. The factor in that half the system, ie the evaporator, TXV valve, blower, etc is buried under the dash where a lot of stuff potentially has to be removed if that part needs repair.
Also, how much it cost to fix a car AC is highly dependent on the parts used. Go to the dealer and pay for a new OEM compressor, receiver/dryer, etc and it's a lot of money. Kind of like buying a shelf or plastic part for a fridge. Use an independent shopt that will offer a rebuilt compressor, aftermarket parts, etc and the price can be hundreds less.
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It's mostly the labor costs. But parts can be costly too, compared to a window unit. Window unit compressors are hermetically sealed with the driving motor, cars compressors are belt driven. Pretty sure car condensers are bigger and more costly. Don't know why. Ever replace a car A/C compressor, condenser or evaporator? Lots of labor digging them out and putting them in. Pretty sure car A/C shops charge you for refrigerant, even if they pulled yours for recycling. But it mostly car mechanic manual labor vs automated factory labor.
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On Saturday, March 16, 2013 6:31:11 PM UTC-4, Vic Smith wrote:

A car AC is a three ton unit.
A three ton unit for your house is likely to cost you about $4000 installed.
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wrote:

In fairness to the price disparity, the home unit also includes an EXTRA motor to drive teh compressor (in the car the motor comes with the car so it's "free") and the home unit also includes a condenser fan this is similarly "free" in the car. And the home unit also has a blower fan that, in the car, is again, "free". Likewise, the duct work in the car is "free". The extra cost to add AC at the factory to a modern car is really pretty low, I'd bet the parts don't amount to more then $500 and the extra labor perhaps $100.
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n buy a room AC to cool a room with the volume of a dozen cars for $100.

led.

I see folks throwing out all kinds of numbers for how many btus or tons a typical auto AC is, but I haven't seen a reference that I'd call credible or rely on. And I'd bet the typical auto AC isn't 3 tons. It's probably more like half that. A car is a tougher environment to cool than a house, but it's also a small volume. One thing that suggest it's not 3 tons is the size of the equipment it takes to get 3 tons of cooling. Anyone think for example the evaporator in a car is anywhere near the size of one in a home 3 ton HVAC?
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It's not designed for efficiency. My 2.5 ton home compressor is small considering there is a motor in there. I recall in my air conditioning book talk about vehicles. Big difference in full size vans vs small car.
Greg
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