Adding AC into my MGB

BlownMGB-V8 · February 04, 2026, 05:33:00 PM

I can relate, it's a bit of a job. Something of the domino effect to I suspect.

Jim

Scott Costanzo · February 13, 2026, 04:07:57 PM

I thought I'd do a quick update. I reached a milestone today, I "finished" the evaporator box.

Here are a few pictures that show some details I may not have shared before. This first one is looking inside the empty box.

Details 1.jpg

This next one shows the evaporator in place.

Detailes 2.jpg

The final one shows the completed and assembled box.

Finished Evaporator Box.jpg

Next is to get the box temporarily installed to prepare for a test.

Scott

Scott Costanzo · March 07, 2026, 04:26:24 PM

It has been a while but I have been working on this everyday I can. So I've been working in the passenger compartment for a little while. This first picture shows how I reinforced the crossbar after cutting out the original structure out of the car for the airbox. It took a bit longer than I thought it would. It isn't quite done yet but it is very close.

This next picture shows the modification I did to accept the air box. I think it looks a lot like what Philip did to his.

Firewall Opening.jpg

Here is the air box in place. The openings I placed in the top and on the sides just fit in front of the crossbar.

Box In Place 1.jpg

I'm currently getting the compressor mounted to the engine. I'm making good progress. I'm hoping I'll have it close in the first half of next week. My overall strategy as the driving season gets closer and closer is to get everything done that needs to have the car off the road first. So I need the evaporator installed and plumbed through the firewall, get the compressor installed with the belt in place and run the bare wiring out to each component. Once I get these things done I can put the car back on the road. I can then run the hoses, lines and wiring to the compressor and condenser and dryer with the car on the road....I hope!

Scott

waterbucket · March 08, 2026, 12:06:42 PM

It's probably of necessity that I have butchered the centre console in a similar fashion except that I angle it towards the gearlever, that is simply so that I can slide my evaporator/air distribution box in from the side rather than from the front. I will start my own AC thread at some point

BlownMGB-V8 · March 09, 2026, 11:43:25 AM

I think that looks really good Scott, and maybe something I should have done as it might have given me a little more room for airflow making the bend to go up. Can you get your cowl vent flap open at all? I get two notches on mine instead of the original 3. I also have a kinda contorted construction for a drip tray that I think could have been better, but that's mostly because the area behind the console is open and used as part of the ductwork. I'm sure there is a better way to do it. You are doing inspirational design work there. Very good.

Jim

Scott Costanzo · March 09, 2026, 08:05:24 PM

Thank you Jim! I appreciate it.

The cowl vent door isn't going work....no room for a door that opens outward. I've got a plan for vent/recirc but I don't think I'm going to have time to do it before mid-April.....I'll need to have the car on the road by then. I may pull the dash this summer and try it. I'll do a post in a day or two with what I have planned if you're interested?

Working on getting the compressor installed now. I'm slow!

Had a bit of a frustrating incident today. I needed to change the disc on my angle grinder so I pulled the nut off and promptly dropped it on the floor. It went into the black hole. It took about 45 minutes to find it! It ended up under the work bench at the very back against the wall. I was making great progress before that happened. Oh well, that's part of the game.

Scott

waterbucket · March 10, 2026, 12:38:04 PM

Scott, my cold air flap will mostly be covered by the top of the evaporator but I have the two air vent holes above it. I am thinking of using one of these or similar: https://www.sheridanmarine.com/product/stainless-steel-sliding-hit-miss-vents Would one of these work for you? Although it would only allow about 50% of air inlet they are slim but might rattle.

BlownMGB-V8 · March 10, 2026, 01:32:09 PM

Quote from: Scott Costanzo on March 09, 2026, 08:05:24 PMIt went into the black hole.

Scott

Yep, those round thingies like to hit the ground and run. I had one do it today too but it didn't get away.

I'm sure we'd all love to see the details of the build.

Jim

Scott Costanzo · March 10, 2026, 05:24:42 PM

Quote from: waterbucket on March 10, 2026, 12:38:04 PMScott, my cold air flap will mostly be covered by the top of the evaporator but I have the two air vent holes above it. I am thinking of using one of these or similar: https://www.sheridanmarine.com/product/stainless-steel-sliding-hit-miss-vents Would one of these work for you? Although it would only allow about 50% of air inlet they are slim but might rattle.

Philip,

Thanks for the link. I had considered something similar but to me it is a short term fix. I have something in mind that may or may not work but I may not have the time to try it this spring. I'll try to detail my thinking below.

The first picture shows my firewall as it is now.

Firewall Idea.jpg

My idea is to cut out roughly what is enclosed in the yellow rectangle. Then create a flap/door that will open towards the front of the car. With some tweaking and using some foam, when it opens perpendicular to the firewall, I think I can get it to block off the intake vent in front of the windshield. I don't believe it has to be perfect.

This next picture is an actuator motor that came with an HVAC box I got out of a Ford Focus.

Actuator Motor.jpg

It was used to open/close the fresh air/recirculate flap in the Ford. It is a two position motor and it's range of motion is 90 degrees. 12 volts seems to run it fine. To reverse it just requires changing the polarity. I'm thinking of using this to open/close my flap. You could use one of those momentary rocker switches that reverses polarity to get it to work I think. I'm not sure this is going to work but I'm going to try it at some point. Hope this makes some sense.

Scott

waterbucket · March 11, 2026, 02:58:22 AM

That's a very clever and neat solution all round, whereas you have a neat plastic box mine is definitely a blacksmith made solution. I had some 1/8" stainless steel plate lying around and it was exactly enough to make my as yet unfinished box, when it looks more complete and presentable enough I will post photos. Your holes through the bulkhead almost exactly mirror mine. Your photo of the actuator has made me think about my demister flap and how to actuate it, due to having side outlets for the footwells and end of dash vets I was looking for a compact solution. I think that I can use remote door locking solenoids to control that flap and that grill or if there is room a flap over those two vent holes

BlownMGB-V8 · March 11, 2026, 07:26:06 AM

Very ingenious. Seems like mine is a bit different, Scott what year is your car again? Mine is a '71 and I don't recall seeing those two holes above the cowl vent flap.

Jim

Scott Costanzo · March 11, 2026, 03:50:12 PM

Philip,
Thanks. I'm looking forward to seeing what you've done with your box.

Jim,
Mine is a 68 and it should be exactly the same as yours. I put the late dash in my car a couple of years ago and I cut those holes so I could get fresh air to the central vents.

Scott