Author Topic: Replacing Evaporator  (Read 1957 times)

Online ehjorten

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Replacing Evaporator
« on: June 18, 2018, 01:49:12 PM »
So, I am going to replace my evaporator.  Service manual looks like it is saying you can just take the inner half of the box off of the firewall and replace the evaporator like that, and not have to take the entire box (including the side with the fan motor) off of the firewall.  I have never done it like that before...seems logical to be able to do it that way, but can anyone confirm?  I am just trying to plan hours of work for a few projects on my next day off.

Thanks,
-Erik-
1991 V3500 - Gen V TBI 454, 4L80E, NP205, 14 bolt FF, D60, 8" Lift on 35s
1977 K20 Silverado - 350, THM350, NP203, 14 bolt FF, D44, Stock Lift on 31s
1969 Chevelle Malibu Sport Coupe - EFI350, THM350
1968 Chevrolet Step-side Pickup - 300HP L6

Online ehjorten

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Re: Replacing Evaporator
« Reply #1 on: June 19, 2018, 06:54:03 PM »
So I replaced my evaporator today and determined that you cannot effectively replace it without pulling the entire box off of the firewall.  I was able to get the one half off and remove the evaporator.  The two studs on the firewall make it difficult and my headers were kind of in the way, but I was able to get the evaporator out.  However...you cannot effectively reseal the box while installing the evaporator and try to get the cover back on.  The butyl rubber tape prevents you from getting the cover back on because you have to sort of slide the cover into place and the sticky sealant prevents that.

So...I dropped my inner wheelwell and pulled the whole box off of the firewall, cleaned it all, cleaned the firewall, resealed the two halves, put sealant all around the box and refitted it to the firewall.  Took me most of a day to do that after trying to do it as the service manual says.
-Erik-
1991 V3500 - Gen V TBI 454, 4L80E, NP205, 14 bolt FF, D60, 8" Lift on 35s
1977 K20 Silverado - 350, THM350, NP203, 14 bolt FF, D44, Stock Lift on 31s
1969 Chevelle Malibu Sport Coupe - EFI350, THM350
1968 Chevrolet Step-side Pickup - 300HP L6

Offline Henry

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Re: Replacing Evaporator
« Reply #2 on: June 20, 2018, 11:44:30 AM »
Hi EH:
Thanks for posting this info...I assume it was the 77 truck you replaced the evap on...I will have to do this some day on my 76 and was curious on how much had to come off. Were your fiberglass box housings solid? Mine look like they are getting fragile and will crack if I apply any pressure to opening them up...I was thinking when I undertake this job to have a fiberglass repair kit handy.
Regards,
Henry

Online ehjorten

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Re: Replacing Evaporator
« Reply #3 on: June 20, 2018, 01:48:22 PM »
Henry;

This was on my 1991 that I am converting to an LS3 6.0L.  I had previously, completely rebuilt my '77 heater box and A/C box.  I have also rebuilt my 1991 heater box, but I had not taken the engine side off until now.

To do this job without getting frustrated trying to access the lower fasteners, you need to remove the inner wheelwell.  This is a pretty easy job and you can get the wheelwell out without having to remove the tire.  You will have to jack up the frame and let the suspension droop to get it out if you are stock ride height, but it is possible.  My 1991 is lifted 8" and getting the wheel well out was no problem with it just sitting at ride height.

When I did my '77 I got a new fan and a/c box out of a wrecking yard from a 1989 Suburban.  It was like new!!!  My '77 evaporator cover was falling apart!  The fan box is injection molded plastic.  The Evaporator cover part is an SMC part (sheet-molding compound, AKA fiberglass).

Be careful with the screws that go into the plastic.  They are easy to strip if you use too much torque.  Also...sometimes when you back-out the plastic screws, they will sometimes strip off some of the threads from the plastic.  Just things to look-out for.

Finally...the halves are sealed and the assembly is sealed to the firewall with buytl rubber.  You can get it in rolls and different diameters, but usually like 3/8" or 5/16" or something.  Window installers will usually have it, or you can get it online.
-Erik-
1991 V3500 - Gen V TBI 454, 4L80E, NP205, 14 bolt FF, D60, 8" Lift on 35s
1977 K20 Silverado - 350, THM350, NP203, 14 bolt FF, D44, Stock Lift on 31s
1969 Chevelle Malibu Sport Coupe - EFI350, THM350
1968 Chevrolet Step-side Pickup - 300HP L6