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Buick Forum: 1993 Roadmaster Estate Wagon: How hard is the evap core to replace?
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  1. #1
    kastein is offline Buick Newbie My Buick(s): 1993 Buick Roadmaster Estate Wagon w/ L05
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    Question 1993 Roadmaster Estate Wagon: How hard is the evap core to replace?

    Hi,
    Found the forum via google while trying to figure this out. Specifically, a thread about replacing the heater core on a 1994, which I believe is somewhat redesigned from the 1993 - I know they changed the engine and parts of the AC system.

    Can I do the evap core without pulling the dashboard out on this thing? It's my wife's and she loves it dearly and I really really don't want to pull any more plastics than I have to, because they are all quite brittle. I've got plenty of practice and a full set of AC tools (gauge set, vacuum pump, UV dye, UV lamp, line disconnect tools... etc etc etc) and have done evap replacements on many other vehicles, but nothing this brittle or sentimental. Normally I'd just dive in and pull the dash. I'm doing an R152a conversion, and since the compressor failed and blew metal dust and shrapnel through the whole system and it's a parallel-flow stacked plate evap core (at least - all the replacement ones I can buy are) I don't want to just try flushing it, though I do have tools to do so. All parts except for the liquid line and evap core will be brand new, and I'm wondering if I should risk skipping the evap core after all.

    It does have the automatic/"fancy" HVAC system, if that matters. I can post the full RPO list when I get home.

  2. #2
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    Re: 1993 Roadmaster Estate Wagon: How hard is the evap core to replace?

    If you had a compressor fail, you really should do new everything. Go to rockauto and get all new lines and everything. Its going to be about 400 to 500 bucks.

    That way, with the proper oil charge, you will be able to get good life out of the system.
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  3. #3
    kastein is offline Buick Newbie My Buick(s): 1993 Buick Roadmaster Estate Wagon w/ L05
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    Re: 1993 Roadmaster Estate Wagon: How hard is the evap core to replace?

    That's actually what I've already planned on doing at this point, in fact the new condensor, capillary tube, seals, compressor, and dryer are on the shelf at home and the new lineset from the compressor to the condensor and dryer got ordered 30 minutes ago, along with a new evap core and the line from the evap to the dryer. The only piece I can't find new is the liquid line from the condensor to the evap, which is NLA from GM and not available NOS anywhere else, nor produced aftermarket. Since it is a single piece of aluminum tubing with fittings brazed to the ends, I settled for running solvent, compressed air, solvent, a pipe cleaner with solvent, and more solvent through it.

    That being said - still interested in whether I'll have to pull the dashboard, which was my original question. I have searched google and youtube for quite some time and the factory service manual (real, official Buick one! It's like 2 inches thick) doesn't clarify much either, it just says start pulling the dash apart. I fear the worst because of that, though I've seen plenty of vehicles where you can get away without doing it through some careful trickery the factory techs didn't come up with. Any idea?
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    Re: 1993 Roadmaster Estate Wagon: How hard is the evap core to replace?

    Sorry...

    I think there was an interior change in 94. My 94 can have the evaporator and HC changed just from under the dash. Not a bad job.

  5. #5
    kastein is offline Buick Newbie My Buick(s): 1993 Buick Roadmaster Estate Wagon w/ L05
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    Re: 1993 Roadmaster Estate Wagon: How hard is the evap core to replace?

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    Forum seems to have eaten my post and sent me to a blank screen... odd. Hope I don't end up posting this twice by accident!

    Alright! Trip report.

    So since there was so little conclusive information on how hard this is to do on 91-93 and 94-96 B-bodies, I went to the junkyard to practice and procure spare parts in the process. I wanted at least a spare fastener collection and the plastic panel that comes off the bottom of the HVAC box, in case I cracked ours trying to remove it.

    First car I worked on was a 94. It taught me that the 94-96 uses the smaller bolt head size (5.5 or 6mm, not sure which - but can measure when I get home) as mentioned in this thread: http://buickforums.com/forums/thread...ce-heater-core

    After working on that car for a while I realized the next one over was a 93, and hadn't been pillaged as badly, so I moved over and worked on that one instead. Bolt heads on that one were 7mm! So the 93-down cars you need 7mm while the 94-up cars you need either 5.5 or 6.

    There are in fact 7 screws holding the bottom panel on. 4 are easy to get at. One over near the trans tunnel is easiest to remove with a box wrench. Another near the firewall absolutely requires a box wrench, and the last one - which is hidden, I can post pics of the bottom panel so you can find your way to it more easily - requires a shallow 1/4-drive socket and a ujoint and extension. Careful you don't drop it behind the carpet.

    I had a dickens of a time getting the evap core out after pulling the bottom panel off, at least until I realized I was getting hung up on the studs that clamp the refrigerant lines to the evap core under the hood. Protip: an external torx socket, size E7, removes those studs from the evap core fittings, making the evap core fit out under the dash much more easily. Unless it snaps them off, in which case use whatever trick you normally use for busted off stud removal. I used boltcutters, because I was replacing the evap core anyways and had a few spare studs at this point.

    The new evap core did not come with sufficient foam weatherstripping, nor was it the right cross section, but I made do. It didn't come with the open cell foam filter pad on the outlet side either, so I transferred it over from the old one. The cross-shaped plastic clips that hold it on just pull straight out, they have barbed tips that grip the fins in the evap core.

    After installing the new evap core (since this is so easy compared to pulling the dash to get to the heater/evap cores on most cars, I didn't do both at the same time as I normally do) the panel goes back on reasonably easily. One little corner of the plastic near the spot where the evap core fittings pass through was being a pain (since it has to go up behind the top half of the HVAC box, and yet has to be snuck in at an angle to get the AC condensate drain tube into the hole in the firewall) so I trimmed about 3/16" off. It presses against a gasket on the firewall there anyways, so I wasn't very concerned about trimming it back some. I don't have a picture of this either, but I can get one if anyone wants it.

    Make sure to not trap the vacuum hoses that dangle at the front of the HVAC box pinched when bolting the cover down. The dark blue and orange ones both tried to.

    The bolts against the firewall were again a pain, but went reasonably quickly once started. Here's a pic of the rough location of the worst one (click any picture to get a full resolution version):


    After that I replaced the condensor, vapor line from the evap to the receiver/dryer, the receiver/dryer itself, the capillary tube, the compressor lineset (warning - the one I bought on rockauto, made by either TYC or Four Seasons, did NOT fit well and had to be custom rebent to avoid kinking the hoses), and the compressor itself. Had to transfer over the high side pressure switch from the old compressor and low side pressure switch from the old receiver/dryer after washing both thoroughly with acetone.

    Just look at all those new parts... I don't want to think about how much I've spent on this now. Probably around 500-600 dollars?


    At that point it was time to do the R152a retrofit! I had put a couple ounces of ester oil (R12 uses mineral oil, R134a uses PAG oil, and R152a uses ester oil) into the new compressor and given it a few dozen turns to spread the oil around before installing it, so I poured the remainder of the 6oz required oil into the compressor to condenser line - to avoid slugging the compressor with incompressible oil - and reattached the lines. Then did the math:
    - original R12 refrigerant mass recommended is 50oz
    - R12 has a molar mass of 121 grams per mole
    - R152a has a molar mass of 66 grams per mole
    - therefore, R152a mass required = 50oz * 66g/mol / 121g/mol = about 27 ounces

    The source of R152a I used for this conversion was Ultra Duster compressed air cans from our favorite chinese tool importer.

    First, I vacuumed the system down to -30inHg, closed the gauge set valves, and monitored the system for about 15 or 20 minutes. There was no noticeable drop in vacuum, so I got out my can tap and put 3 10oz cans (slightly over recommended - but should be fine) of R152a in. This was actually the cheapest part of the entire project, since that's about $15 worth of refrigerant. As a bonus, R152a has no ozone depletion potential and a far lower global warming potential than either R12 or R134a, while working far better as a refrigerant than R134a and almost as well as R12. Win/win as far as I'm concerned!

    It works! She's really happy with it, first time the car has ever had working air conditioning while she owned it. Only complaint now is that it seems to blow colder air than it should given the temperature set on the fancy automatic HVAC control panel! I'll take that as a sign of success.

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