OEM vrs aftermarket AC Evaporator? Copper vrs Aluminum?

[ericthered]

This discussion relates to an AC problem I am having in my 2006 M35
climate-control-problem-left-side-blows ... 94185.html
Recently my factory evaporator was replaced with an aftermarket evaporator ($65 - $100 US). (An OEM evaporator is $375! with discount ) The factory evaporator failed when the expansion valve was being replaced.


BUT now, my AC blows much warmer on the left side than the right side. ANd significant troubleshooting suggests everything in the HVAC is working "right", leading me to the question whether the aftermarket part performs poorly versus the OEM part.

Here is what I've come up with:

http://www.refrigtech.com/Knowledge_Cen ... System.pdf

The drop in air temperature is greatest across the first row of the coil and diminishes as the air passes across each succeeding row. The fact that the temperature difference between the air and the refrigerant is greatest across the first row, and becomes less and less as the temperature of the air is reduced in passing across each succeeding row. The temperature difference is least across the last row of the coil.

• It's a fact, evaporator temp varies across the fins - but by how much in this application?

From: http://www.achrnews.com/articles/87135- ... oil-debate
"one of the biggest problems with aluminum is that leaks can occur where the aluminum meets the copper in the condensing unit due to galvanic action."

• So copper parts are more likely to fail than pure aluminum - I have heard that all aluminum evaporators are very reliable. Could copper be responsible for the factory evaporator being prone to failure?

“Aluminum is roughly the same price per pound as copper, but you use three times as much copper in a copper coil. It does have an impact on manufacturing costs,”

• It's much cheaper to use aluminum than copper. Should I assume the aftermarket part is aluminum? probably

From an article on Wikipedia titled : "Copper in Heat Exchangers”.
Scrolling down to Thermal Conductivity it reads : Silver - 247.87, Copper- 231, Gold - 183, Aluminum – 136.

• Copper is 59% more thermally efficient than Aluminum!

• Copper tubing is also thicker than aluminum, to further increasing the side-to-side thermal conductivity

My question now,
==> is the factory evaporator made of copper or aluminum? And is the OEM replacement part also made of copper?

==> Any insights on whether this theory makes sense, or am I prone to dreaming up technical conspiracies?

THANKS!

Added info:
Here are two pics of a used OEM evaporator:



and here is a pic of a new UAC aftermarket evaporator:


note: I'd also expect that thinner aluminum evaporator cores cool down the car quicker than thicker copper tubes

[Ilya]

Those look to be aluminum but I'm no expert...sucks that you're still battling this.

[Larz]

I don't see any copper in any of those pics. Your questions made me curious about copper V aluminum. Most of what I read online seems to be about household HVAC units, and the 'experts' quoted in those articles seem to be split. About half recommend copper and the other half, aluminum. From a repair point of view, aluminum is almost never repairable, hence the replacements when a leak occurs. They also point out that copper is thicker and less likely to develop leaks, while dissipating heat more efficiently. I can see why car makers use aluminum: It lowers the cost of manufacturing and usually lasts well beyond the warranty period of the car, so it is unlikely the manufacturer will need to replace it at their expense.
For your situation, it took 8 years for your evaporator to fail. A copper replacement might last longer than 8 years, but even if it did, will you still have the car in another 8 years? If you will keep the car that much longer, maybe go for the more expensive copper unit. If not, I say take the same path as the car maker.

[ericthered]

Larz,
I agree the factory unit looks aluminumish in the pic, I'll call Infiniti and see what their OEM parts guy thinks their part is made from, if they have one. If anything is made from copper, it's the factory evaporator, but no guarantee.

As far as 100% Alum vrs Copper for any application, all aluminum doesn't fail due to corrosion, plus aluminum is lighter and copper is expensive. Like you said, an Aluminum evaporator can't repaired in place - as preferred by many HVAC repairers. But that is not at issue in an auto.

Back to the M:

• Maybe the OEM evaporator turns out to be aluminum. Is it reasonable to think an OEM evaporator cools more evenly than an aftermarket evaporator?
  Has anyone here replaced the evaporator in their M?