300e ac evaporator core is toast

Hello,
Just found out why the ac in my '89 300e won't hold a charge--mechanic says the evaporator core has failed and he needs $1,600 bucks to install a new
one. I've never installed one myself but it looks like I'm going to now because I've got more time than I do money.
Several mechanics have told me that the whole dash has to come out to get it out and I don't doubt it. I'm not looking for a step by step by any means, just any tips for avoiding the big "gotchas" and things like..
how long should it take me (of average or better skill) to do the job if I need any special tools how I can check for leaks after it's installed but before I re-install the dash if there are any other parts that I should also replace while the dash is out and who's a good source for the core
Also, I can hear one of the flaps in the ac ducting making a thumping or popping noise about every second or so (when the ac's on of course) and there is little or no air coming out of the center vent. Is that because one of the actuator pots has failed or is it something else? Can I tell if the pot has failed by inspecting it visually or do I need to take a vacuum on it to find out?
As for the cost of the part(s), thebenzbin wants $282 with the "valve", $186 apparently without the valve, and ACKits wants $145 also without the valve. Is one of these going to be better quality than the other and should I replace the valve also.
My last question has to do with the cost I was quoted by my mechanic. Both of the evaporator cores on thebenzbin have a suggested retail price of $960. I know for a fact that my mechanic has charged me or quoted me the exact same suggested retail prices shown on this website for several other high dollar parts and I'm wondering if $700 or so of that $1,600 bill is a markup for the difference between the two costs of the part? I'm not grudging my mechanic the ability to make a decent living but is it customary and does it seem right to charge $70 per hour to do the work AND markup a $200 or $300 part 300 to 400 percent?
Thanks in advance for your guidance and comments.
Mike
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Yep, that $700 markup is true. But before you change out the evaporator on your car... check for leak at the expansion valve... it is very easily missed and declared that the evaporator is leaking.
Just follow the AC line going toward the interior of the car... they probably already did the dye injection... it is kinda just below your wiper location way deep inside... if you can flash some light in there... if you see alot of light green colors, then you know it is leaking like crazy there. If you get the UV lightpen, it will glow purple/green.
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cold air ceased after about 1 week. To fix my MB trained specialist injected some AC leak stop (similar to the aerosol stuff you put into tyres to fix punctures) into the AC line and after regassing I've had no more problems and the AC is freezing. Try this fix first, it could save you a fortune.
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I would recommend this too... Check for major leak first.as I mentioned before.
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Thanks for that suggestion. I'll look into it and I wonder why neither of my mechanics have suggested this as a possible solution?!?!
Thanks,
Mike

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There is no money in it for them. Also most shops do not work on AC units that have had sealer installed. The problem is that some sealers use hydrocarbon as a propellant which is considered a contaminant which fouls their recycling equipment. The following site has some good useful info. www.cliplight.com/ssp.php
Peter
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Hello Peter,
I was wondering if there might be a hidden cost to the sealer and have pretty much decided to replace the coil anyway. Never had much faith in sealers and glues of any kind anyway. Thanks for the link and your comments.
One other question I have concerns the hose assembly that this car requires. Do you or anyone else have any experience with whether it is usually replaced regardless of its condition? It's a $460 part but I also assume that it's out with the dash again to replace it if it fails. Same for the $280 worth of vacuum actuators I suppose.
Thanks,
Mike

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There is no hidden cost to the sealer... the only way the sealer harden is when exposed to air. Otherwise, they are safe enough as long proper procedure is observed when servicing A/C system... which is complete evacuation of all freon before breaking the seal in the system for replacement.
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