I thought I'd share my current winter project, which is adding AC to my car. I've actually been working on this for a little over a year now, mostly planning and gathering parts. I will state in this first post that I think very few of you would take an approach like I am when there are "easier" ones out there. I have goals that aren't easy to reach with the available off the shelf units without spending a lot, which I don't like to do. :D I won't go into all of those details now. I'll touch on them as the build proceeds. So the video below shows a proof of concept I built to verify the MGB fan (with a Fiero fan motor) can supply enough air for the HVAC system. I used cardboard and included the evaporator as well. It's rough but I was pleased enough to proceed with this phase of the build. I will update this thread as progress is made.
Scott, I am also trying to improve the heater and add air con to my conversion, due to it being a relatively rare engine swap I am doing as much as possible before the engine finally goes in. I think the factory was more interested in getting warm air to the footwells that the future installation of aircon. apart from the two openings that let air into the footwells there are just two small holes (11/2"-13/4"?) to let air into the rest of the cabin. I have enlarged those two holes into one single hole about 10" x 4". I have found a Land Rover Discovery heater matrix that fits in the gap between the engine and passenger sides of the bulkhead. Not really sure if the original matrix restricted the flow but this one certainly doesn't. I will add photos when I have figured how to. ;D
Quote from: waterbucket on November 30, 2025, 02:00:21 PMScott, I am also trying to improve the heater and air con to my conversion, due to it being a relatively rare engine swap I am doing as much as possible before the engine finally goes in. I think the factory was more interested in getting warm air to the footwells that the future installation of aircon. apart from the two openings that let air into the footwells there are just two small holes (11/2"-13/4"?) to let air into the rest of the cabin. I have enlarged those two holes into one single hole about 10" x 4". I have found a Land Rover Discovery heater matrix that fits in the gap between the engine and passenger sides of the bulkhead. Not really sure if the original matrix restricted the flow but this one certainly doesn't. I will add photos when I have figured how to. ;D
Hi Philip,
Yes, the original heater fan housing was somewhat restrictive. I'm also doing unusual things too. There isn't much room in an MGB. I'm removing the flap thing that directs the air flow to the floor/windshield and running the air out of the bottom of the fan housing to the evaporator housing. It's hard to explain so this picture may help.
20251130_143510.jpg
There are a lot of details that will become clear as the project proceeds. The possibility of a spectacular failure exists as well!!
Lots you can do. That Disco core sounds interesting. Do you have a picture of it by chance?
With the flap gone something is needed for defrost and how much really depends on airflow. That can get tricky, probably best to overdo the air to the windshield if you can.
Jim
Quote from: BlownMGB-V8 on December 01, 2025, 05:39:25 PMWith the flap gone something is needed for defrost and how much really depends on airflow. That can get tricky, probably best to overdo the air to the windshield if you can.
Jim
Jim, I'm absolutely maintaining defrost capability. You never know when you're going to need it with the way we use our cars.
Scott
I can easily take a photo but I have as yet not managed to upload one. I have resized them to the old standard and dragged them onto my reply where it stays for about two seconds before disappearing back from whence it came. The solution is probably obvious to anyone bar me. ;D
Carl can help you with that I imagine, but are you using the quick reply or the reply button? The full window has a big full width button below to attach files.
Jim
Quote from: waterbucket on December 02, 2025, 03:27:37 PMI can easily take a photo but I have as yet not managed to upload one. I have resized them to the old standard and dragged them onto my reply where it stays for about two seconds before disappearing back from whence it came.
Philip,
As Jim B suggested, use the regular "REPLY" button not Quick Reply. Then click on the "Click or drag files here to attach them." bar. That will allow you to choose a pic from your computer/device.
On a mobile device, you may have to tap "User Actions" to access the regular reply button.
For now, it will still be a clickable thumbnail at eh bottom of the post
Everyone, I'm assisting Philip with his attachment issues. I was going to edit one of his posts with this but decided a new post would be better. The following are Philip's words. Philip, correct me if any of this is not correct:
The one of the hole in the bulkhead is taken from the brace that goes from the top of the tunnel to the cross tube that is at the bottom of the dashboard. The hole in the foreground is for the evaporator drain, beyond that is the hole for the evaporator to sit against and beyond that is where I enlarged the two small circular holes to increase airflow.
cid_ii_19ae5bdc68c4c8405f61.jpg
The Discovery matrix fits in between. The general mess around the area is the paint polishing compound that got everywhere and was resistant to pressure washing.
Screenshot_20251204_133502.jpg
I'll add more later but believe it or not, Philip and I are following very similar paths. My next step, once I finish modifying the fan housing, which is taking much longer than expected, is to do the bulkhead modification Philip has done. Very strange. This should be very interesting!
Scott
Not that much different from what I did really, same sort of enlargement of the air holes and such. I did manage to retain the cowl vent flap which reduced the area available for air to move up to the evaporator which I placed just above the square tubing brace. Your evap is wider but considerably thinner, I'm looking forward to seeing how you guys position that. Handling the condensate was an interesting challenge, collecting that while getting the air around the collection tray. I expect it could have been done better than what I ended up with.
Jim
Quote from: MGBV8 on December 03, 2025, 10:32:51 AMQuote from: waterbucket on December 02, 2025, 03:27:37 PMI can easily take a photo but I have as yet not managed to upload one. I have resized them to the old standard and dragged them onto my reply where it stays for about two seconds before disappearing back from whence it came.
Philip,
As Jim B suggested, use the regular "REPLY" button not Quick Reply. Then click on the "Click or drag files here to attach them." bar. That will allow you to choose a pic from your computer/device.
On a mobile device, you may have to tap "User Actions" to access the regular reply button.
For now, it will still be a clickable thumbnail at eh bottom of the post
Carl, I have got it sorted now. As Jim correctly said it was a simple case of not using the quick reply. I will start updating the build journal.
I think one major difference between Scott's AC and my attempt is that he is retaining his OE vents in the dashboard whereas I am putting a double DIN stereo there with car play so that I can have an easy to read Google Maps. Being profoundly deaf I cannot rely on hearing the sat nav's verbal directions. We are also getting an increasing number of cameras that can detect any use of a mobile phone which is what I normally use to find my way around.
Quote from: BlownMGB-V8 on December 04, 2025, 10:32:42 PMNot that much different from what I did really, same sort of enlargement of the air holes and such. I did manage to retain the cowl vent flap which reduced the area available for air to move up to the evaporator which I placed just above the square tubing brace. Your evap is wider but considerably thinner, I'm looking forward to seeing how you guys position that. Handling the condensate was an interesting challenge, collecting that while getting the air around the collection tray. I expect it could have been done better than what I ended up with.
Jim
Jim,
This is how I'm handling the condensate.
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I took this from an HVAC box I got out of a Nissan Rogue. My evaporator will be living in this box.....well, not this box exactly. I'll be fabricating a box with HDPE using what you see below as a pattern. It will be sitting on the transmission tunnel between the radio console and the firewall.
cid_e546d554-607c-462a-a62c-bbcd8e0c8038.jpg
I'm a little surprised there is enough room for that, but we do have to make use of every possible inch. My tray being as large as it had to be sure complicated matters, running wide where yours goes tall. You probably have better packaging. When I bought my core I was really only thinking about maximizing capacity and giving little heed to drainage and airflow.
Jim
I won't add any more photos after these, I may start my own HVAC thread rather than distracting from this one. The first photo shows the Discovery heater matrix in the bulkhead gap it just squeezes past the steel tube mount for Toms knob.
The second photo shows the Discovery matrix in position, there are at least two variations of this matrix and only the shortest in height will slide in. You can also see the shelf for the evaporator/distribution box to sit on, I had to cut away that ridge underneath the bulkhead for gearbox clearance this shelf became a two in one solution. I also removed the brace from the cross rail tube down to the tunnel and replaced it with a new one which is angled more towards the back of the car, I can just squeeze in a a 8" cube that houses the Ford Fiesta evaporator and the outlet pipe to the vents.
The last photo shows the matrix itself, they are cheap to buy over here from Ebay.
I've been modifying my fan housing in an attempt to make it more efficient. It worked pretty well with the setup I've been using for the past 8+ years and also with the mockup I showed in the first post above. I'm never satisfied it seems. Anyway, this first shot shows where I stand at the moment.
20251208_144007.jpg
Nothing is welded in this shot, I'm still fabricating things but this gives you and idea of what my goal is. When I first reinstalled the heater in the car after the LS conversion, I went to a Fiero fan. In addition, I had to modify the housing because I modified the firewall which changed the size of the fan housing mount. I also had to place the fan so it didn't interfere with the engine head and intake...it's close. Anyway, all of this resulted in the fan being placed in a suboptimal position within the fan housing. Since I'm needing as much flow as possible, I decided to do what I could to make it the best I could. I have a HVAC box from a 2011 Nissan Rogue (long story) which happens to have a squirrel cage that is the same diameter as the Fiero squirrel cage. Here is a picture of the Rogue fan housing:
20251110_091237.jpg
I decided to use it as a model to place the fan in the MG housing since it is likely much more efficient than what BMC did 60+ years ago. That required some modification to the fan housing itself which you can see in the next picture below:
20251111_145851.jpg
You can see the cardboard template that I made to duplicate the dimensions of the Rogue fan housing. What it looks like I will end up with won't be perfect because of packaging issues (fitting 10 lbs. of poop in a 5 lb. bag ;D ) but I'm pretty pleased with the way things are going. I can't wait to test it out. I'm guessing I have another couple of days to finish the fabrication.
Scott
I applaud your efforts and hopefully that will do the trick. But if not, at least there is an option to use a high speed motor. The Fiero probably hits somewhere between 1000 and 1200 rpm loaded. If you can double or triple that the airflow should go up significantly. A steel fan should be fine up to something close to 6k, (but test) plastic also probably.
Jim
It's been a while but I have been steadily working through things. There haven't been any real milestones to share but I thought I'd show where I am with things. So far, everything is going as expected.
This first picture shows the completed fan housing modifications. it's a little hard to see but I grafted what I will call the trough from one of my OEM fan housings into the B fan housing to help seal the open end of the squirrel cage. It's on the perimeter of the intake opening.
Fan Housing.jpg
This next image, with the fan installed, gives a little more detail on the trough.
Fan trough.jpg
This last picture shows the early stages of the evaporator box construction with the evaporator in place.
Evaporator Box.jpg
I'm currently in the process of modifying the car to fit the ducting/evaporator in order to mate the exhaust from the fan housing to the ducting/evaporator. I hope this phase will move a little quicker than things have so far. I'm having a lot of fun with this so far.
Scott
Looking good Scott. The seal at the end of the squirrel cage is pretty important and you have little choice except to use some version of close end clearance with possibly a labyrinthine type seal which is tricky given the nature of the fan itself. One of my donors used a bell that curved around to the inside of the fan blades, meaning that it covered the ends of the blades. If you think about the airflow that means it blocks off the escape path past the blade end by using both that and any air that escapes past the end gap. I think they are probably effective enough to tell so I used that in my housing. It might create a little inflow turbulence right at the edge of the bell but probably not as much as that created by the blade ends. It seems to be a pretty common construction for pumps and turbines.
Jim
More progress made. First, I wanted to show how I'm attempting to seal the fan housing. I'm being anal about this based on what I'm seeing in OEM units. Obviously, they are sealed against air leaks so this is what I'm trying:
Fan Housing Front Cover.jpg
So I've been working on the evaporator box which turned out to be more complex than I imagined. No issues with that but it is taking a bit longer than I anticipated. Here is it's current state:
Evaporator Box Side View.jpg
It still has a little way to go but I'm very pleased where I am at the moment. This next photo shows how I intend to place the outlets in the top cover.
Evaporator Box Tentative Outlets.jpg
This next photo shows how the evaporator box will interface with the bottom of the fan housing. It isn't exactly where I want it at the moment, but it is very close.
Evaporator Box Fan Interface.jpg
Once I get the evaporator box sealed up and make a few additional modifications to the firewall, I'm not terribly far from doing a quick test of the system. It's getting there bit by bit!
Isn't it a little cold to be talking about air conditioning Scott? :o
Seriously though, it looks good.Do you think your airflow will be enough to avoid ice build up?
Jim
Quote from: BlownMGB-V8 on January 27, 2026, 11:17:17 AMIsn't it a little cold to be talking about air conditioning Scott? :o
Seriously though, it looks good.Do you think your airflow will be enough to avoid ice build up?
Jim
Jim,
Based on the testing I did with a leaky cardboard mockup, (see the very first post in this thread) there should be plenty of air moving through the evaporator.
Scott
Quote from: BlownMGB-V8 on January 27, 2026, 11:17:17 AMIsn't it a little cold to be talking about air conditioning Scott? :o
Seriously though, it looks good.Do you think your airflow will be enough to avoid ice build up?
Jim
From what we are reading over here the air coming out of the air con might be warmer than ambient! ;D
Yesterday it said Kentucky was going to be hit hardest. Keep warm.
Warm? What's that? Actually we were considering moving into the basement if the power goes out. Might be easier there.
I find I can't go out out in the garage or the sun room anymore. It makes my fingers hurt. Is that old age? Is it something I need to see a doctor for? I know I never had that problem last summer at all.
Jim
I thought I'd do a quick update. I finally got the modifications to both the car and evaporator box done so I could line up the evaporator box and fan housing outlet. It's a little hard to see in this picture but it was taken inside the fan housing showing the outlet and the evaporator box inlet. The foam you see will hopefully seal any leaks at the interface.
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I'm very close to completing the evaporator box at this point. It's amazing how many details there are in building the box!
I can relate, it's a bit of a job. Something of the domino effect to I suspect.
Jim
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
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.
Reinforcement.jpg
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
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
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
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
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.
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
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
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
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
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
Aha! Then you don't really need the flapper door do you?
Very slick. I can't do that though as the area is covered by my evaporator.
Jim
I thought I'd do a quick update. I've been spending a lot of time on this project and I'm making good progress. I'm finally at the point where I can test the air flow through the system and did this afternoon. I was pleased with the result. Here's a quick video.
Here's a photo of the duct work I came up with.
20260408_140410.jpg
It's a long story to describe what's going on in this picture and I'll go into more detail at some point in the future. Let me know if you have any questions. I hope to have the car close to being back on the road in the next week or so.
Scott
I'm making some progress and I thought I'd go into some of the details on the AC build.
First, the evaporator is installed in the car! It is a significant milestone for me. This first picture shows the view from the passenger compartment.
Evaporator pic
The firewall cover you see took a bit of time to fabricate. The following picture shows some of the details of it.
Evaporator pic
The evaporator manifold protrudes forward of the inner firewall which is why you see the opening in the center of the right cover. The two holes are for the suction and discharge lines obviously. I modified them slightly to ensure the lines weren't rubbing against the edge of the sheet metal. I used something called tar tape to insulate the tubing in the manifold and put a thicker amount of the stuff around the area that goes through the cover to seal things up. On a side note, that tar tape is thick, sticky, nasty stuff to work with but it does the job.
I don't have a great picture of the completed manifold but this next picture shows the first version.
Evaporator pic
My friend Cris welded the manifold together for me. Originally, I was going to use it in a modified OEM box but I decided not to go that route. This next picture shows the modification needed to get through the outer firewall in an advantageous spot.
Evaporator pic
The two pipes you see taped together were welded by Cris.
Finally, this photo shows the lines through the outer firewall.
Evaporator pic
The final subject for this post is the ducting to get the air where it needs to go. Here is a better picture of the ducting.
Evaporator pic
What you're looking at has gone through many modifications and it looks it! In case you haven't noticed, there isn't much room in an LBC! 😁 So I started with an idea and built it with the intention of modifying it to fit. It took a while. If you've read this far, I'll try to explain what you're looking at. The colored dots will hopefully help.
The purple dotted ducting is obviously the vents at each end of the dash. The blue dotted are the floor vents. The red dotted are for the center vents and the orange for the defroster. As you may notice, I'm feeding air to both the center vents and defrosters via a single opening in the air box. I'm doing it this way mainly because of available real estate on top of the air box. I cut a single oval hole that has an open area of approximately a three inch hole. What I'll call the manifold on the center top of the air box is formed from 1/16" thick PVC plastic. I created, with help from youtube, few different patterns to create different tubing components for it. They were formed with a heat gun and glued together with hot glue. At the bottom I started with an oval to round tube (to convert to oval hole in the air box to a round hole). I added a 2.5" Y to the top of it. On one side of the 2.5" Y, I added a 2" Y for the center vents. On the other side I added a 2.5" Y with a valve in it, that I purchased from Vintage Air, for the defrost vents. 2.5" was the smallest diameter Y with a valve I could find. I wanted a 2" unit. Anyway, I managed to fit all this behind the dash but it wasn't feasible to add all the ducting needed because of the lack of room. After several mods, I ended up with what you see in the picture. Oh, it's kind of hard to see but there is a white dot which is right next to the lever for the valve in the Y I mentioned. I'm in the process of adding a cable so I can control it with the factory defrost/floor knob.
This turned out way longer than I intended but there are a lot of details that I wanted to catalog.
Scott
That's looking very good, I haven't done anything to mine since I last posted. I have used sis 13/4" stainless exhaust elbows that were left over, as I have said blacksmith fabricated! Car Builder Solutions have those Y divertors in 11/2", 2" and 21/2" Although they are UK based they are very competitively price and ship the same day. Barry Braxton has bought quite a bit from them and my air vents are theirs as well. You can download a catalogue from their website; https://www.carbuilder.com/