DIY - Aftermarket Evaporator Installed In A Coupe

Hi Team. I set out this year to find a replacement evaporator for the AC systems in our E9s and E3s (and E12s and E21s).

I found one (originally made for a 2007 Land Cruiser). It fits in the original box pretty well and it’s in my car working now. I’ll show you how I did it and then update you at some point in the near future as to whether there’s any advantage to it over the original parts. This is a work in progress and you are joining me in the experiment!

I want to emphasize that many members on this board have made their AC systems work pretty well using the original BMW parts and that if you are in need of better cooling in your car start with the basics by making sure your system is charged with the correct amount of oil and refrigerant; making sure that you’ve cleaned the bees out of your condenser; inspecting your switches and wires; checking if the seals are still there on the little flappy doors inside your heater box; and seeing to other correctable things.

On the outset, I wanted to find an evaporator upgrade method made from cheap, commercially available, and reliable parts that could be shared as a DIY guide that anyone could follow. How’d this turn out?

Is it an upgrade?: TBD
Is it cheap?: Pretty affordable I guess. See the spreadsheet below.
Is it reliable?: I already feel better knowing that the connections have o-rings, not copper washers.
Are the parts commercially available: Most yes, some no.
Can anyone do this?: Yes, except for a few parts which are hard to fabricate. Read on.

Here is the stock evaporator box with its big tube-and-fin evaporator.

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Here’s the old evaporator and associated plumbing.

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Here are the new evaporator, thermal expansion valve (“TXV”), and associated plumbing:

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I modeled all of these parts to make selecting an evaporator from the Internet easier. You can see here that this new evaporator isn’t quite as tall as the old one but it fits in the box snugly against the blower cavity despite not being quite as tall as the old one.

1623269726336.png


Below are all the parts needed for this conversion as well as a source for them (in the spreadsheet). This assumes you have an original AC box with a working blower assembly and that you’re willing to modify the box.

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Here is the kit assembled and in the box (top view):

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Thoughts and reflections:

I’m pleased! It’s been cloudy but I got a sunny day today finally. I got a chance to run the system starting with an interior temperature of 107º. I was measuring temperature drops (measurement of air going in minus air coming back out) of as much as 35º as the cabin cooled down. I’m going to keep tweaking some things to see if I can get more cooling.

I didn’t make any modifications to the blower even though it is probably the biggest limitation in this system. I’ve determined that the blower (with whichever evaporator is in the box) makes about 190 cubic feet per minute of airflow. If I’d found a way to switch the blower and the evaporator at the same time in this experiment there’d be know way to know which made the bigger difference.

I wanted this to be made completely from parts anyone could source. The 3D printed stuff I’m kind of excusing here since there are probably dozens of ways to secure an evaporator in a plastic box and 3D printing was just the easy way for me. Also, I can share those files with anyone who wants them.

As far as the fit of the new system, it was kind of a bummer that the TXV interfered with the back of the box since it was almost a perfect match. Have a look at this cross section:

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View from the bottom of the valve and the box cutout:

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A window shaped like this needs to be cut out from the box. Aside from that, the only other modifications to the box is a few screw holes.

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The blue plate (part D4 on the illustration) is a shell that makes a little more clearance around the TXV (particularly at the bottom) and also collects dripping condensate and returns it to the bottom of the box using gravity. I have it installed pressed against a foam seal and I’ll be checking it periodically this summer to make sure it doesn’t leak. It could also be glued in with silicone.

The real missing link I couldn’t find on any website was an adaptor from that particular TXV to an O-ring-stye connector and a clamp to squeeze them on. I’m referring to parts C3, C4, and F on the diagram. I made the adaptors on my little lathe and brazed them to tubing.

1623270077890.png


This was my first time brazing. It seems to have worked well but I know this option isn’t easily available to everyone at home.

Presumably I or someone more experienced than me could make this assembly into a kit if the DIY route is too confusing. Also, I took all the pictures needed for a full "how-to" guide. But I think anyone with enough ability to take their box out of their car and / or charge up an A/C system should be able to assemble this.

I have enough parts for another prototype if someone with time on their hands wants to reimburse me for just the parts and postage. All I’d ask is that you’d be able to compare this system with the previous one in your car and report back for everyone’s benefit.

Anyway, it can now be said that someone has used a non-original evaporator in an E9. I’ll post a critique of the function soon. So far so good. Thanks for following along!
 
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Dick Steinkamp

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Thanks to Blinkling for the write-up on the tube locations; we've been having sidebar discussions on that for awhile. And many thanks to Dick for the capillary tube experiment! I put mine in where Blinkling's evaporator was originally designed to accept it but now I think I'll relocate it into the fins of the evaporator. While I have the thermostat out, I'll check the set screw adjustment as he described.

Great stuff, many thanks to both of them!
Actually it was the master scientist David (@Blinkling) who did the capillary experiment. I've been leaning on David and Alan to provide info and answer questions. Both have been very responsive and helpful.

I have come up with a method to run the hoses in the cabin what works with David's supplied evaporator pipe set up...

IMG_7329.jpg


It's a little fussy getting the #10 hose to clear the HVAC controls, but it does.

At this point, I think the best solution is to use reduced barrier hose (smaller OD...it can be bent into sharper turns without kinking). This eliminates the need for custom copper piping in the cabin, uses all modern O-ring fittings, and eliminates at least 2 fittings (the fewer fittings, the less the possibility of leaks). Thanks Alan for this idea. You will need to supply David with the length the pipes need to stick out of the new evaporator in order to be able to hook to them with 90 degree fittings as shown in this example...

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I am going to use R134a in mine, primarily so that I can have an AC shop go over my installation and pull a vacuum before charging, and install dye and check for leaks. I'll post here with the quantities of R134a, compressor oil, and dye that the shop computes.

I'll also post my wiring diagram using most of the stock system with the addition of a Trinary Switch to monitor system pressures and to turn off the compressor if pressures are too high or too low, and to automatically turn the condenser fan on and off as needed. I've also relocated both the high and low service ports to make them more accessible. I'll post pictures of those too.

I'm still a ways away from completion. Give me a couple of weeks.

Thanks again to David and Alan!
 

ATL_Alan

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Oops, thanks to David for the capillary experiment! Read it early this morning before getting fully caffeinated and didn't get the attribution correct.
 

jjs2800cs

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We have the opportunity to explore this approach to the evaporator short comings.

Our 2800CS is totally apart for restoration, and one of the areas we are focusing on is the AC system. Already have in hand a parallel flow condenser, new real Sanden 508, etc. We have capability to make our own hoses, vacuum the system, etc. Also after much discussion, have decided to go with R134, instead of the R12. Lastly we have been following the efforts in this thread with great interest.

We have a complete spare AC evaporator housing and heater air box out of a doner car. The originator evaporator and heater box have both been cleaned and refreshed, with a replacement expansion valve installed, are on the shelf ready for installation when the time comes.

So in the meantime we are considering modifying the spare AC box with this approach. Thus here are our questions.

to Blinking?
I'm unclear if you are willing to provide a kit, maybe with less the evaporator core, expansion valve, and other over the counter items? Can you supply the fittings, printed spacers, etc, you developed? You can PM me with details, cost etc.

Also in this thread this is briefly discussed.


where this might be an alternative. Is this the same core with a different expansion assembly. There is a statement that it could be turned around and any u-tubes would not be necessary. Please explain if possible?

Thanks to the other who have already done this. Living in west coast of Florida, with usually 90 degrees and zillion percent humidity in the summer, we want better AC.

jjs2800cs
 

Dick Steinkamp

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I just realized I did not post the amount of 134A my system took and my wiring diagram.

Essentially, the shop had to guess at the amount of 134A needed since the system is custom. They adjusted their guess once they had the system up in running and could read pressures. In the end, the system took 1.75 pounds of 134A. My compressor came with the proper amount of oil. About an ounce was removed and replaced with the same amount of dye.

Here is a stock wiring diagram (thanks @HB Chris)...

Screen Shot 2022-06-12 at 10.25.00 AM.png


When the AC blower switch is turned to the first position to the right, the changeover relay is activated which makes the heater blower inoperative. It also sends 12v to the temperature switch. If the temp switch is calling for cold, it sends 12v to the compressor clutch to operate the compressor and to the relay by the radiator which closes and turns on the condenser fan.

A simple system, but all modern systems now incorporate a trinary switch in the high side of the system to prevent the compressor from running if the pressure is too high or too low to be safe AND to run the condenser fan only when needed. For example, when you are running down the highway there is generally enough air flow through the condenser without the need for the fan to be running.

Here's the system with the added trinary switch...
IMG_8229.JPG



The AC blower switch via the temp switch now sends 12V to the trinary switch when the temp switch is calling for cold. If the trinary switch is seeing between 30 and 406 pounds, it passes the 12V to a relay which closes and turns on the compressor. If it doesn't see these pressures it will not pass the 12v to the relay. (NOTE: This relay is probably overkill. I think you could run the wire from the trinary switch directly to the compressor clutch instead of passing it through a relay. The relay is not much more work, however)

When the trinary switch sees 254 pounds or more, it completes a ground which energizes another relay, which closes and sends 12V to the condenser fan. This way the fan only runs when needed. I'm using switched 12V to trigger the relay, but I guess you could use "always on" 12V if you want the fan to run with the engine off.

My AC blower switch worked fine so I saw no need to replace it. If you replace yours, you will either need to figure out a way to wire it to also energize the changeover relay, or just remember to insure the heater fan is off when you run the AC.

All the other parts on my system are new. All O ring fittings. The vibration damper was removed (not needed with a rotary compressor). The new receiver/dryer incorporates the trinary valve as well as the high side service port...

IMG_8228.JPG
 

Blinkling

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Thanks for posting those schematics, Dick! I also used a relay to control my compressor field coil.

Here's an added complication for anyone who wants to use it: I have a second relay in series that grounds through the oil pressure switch (and a diode!) so that the system won't run unless the engine is running. When I start the car with all the switches in the 'on' position I hear compressor engaging right as the oil pressure light on the dashboard goes dark. And when I shut the car off I hear the fan running for a second or two while the oil pressure in the engine drops down to zero and the oil switch opens. As stated you'll need a diode between the relay and the oil pressure switch but you'll also need one for the oil pressure lamp wire or else the AC system could cause the oil lamp to not light under certain conditions. EDIT: The only advantage do this complication would be so that the compressor and fans aren't trying to run during starting. It's a sort of load shedding function while the engine is cranking and stumbling to life.

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@jjs2800cs: I got your PM and I'd love to help! I'll answer what you typed above here in the thread in case anyone is wondering the same things:

1. I can supply just the adapter parts if you have an evaporator and valve;

2. That assembly from that donor car was a big part of my initial plan but the custom-fitting parts ended up being better for a few reasons. Here's a graphic from that auction (before it disappears):

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Luckily I found a valve that is identical in dimensions and specifications but which has no electric valve on it. Check out the part numbers on page 1.

3. Interestingly, this evaporator has a single fitting with a pair of identically-sized ports on it so there is no obvious 'in' port or 'out' port. There's an off-center locating pin between the ports that keys the expansion valve to the 'correct' orientation but we can just press that out and flip the parts whichever way we want since this is a custom application. This all means that you can put the evaporator into the original BMW box rotated however you want (fittings on the driver side of the box, fittings on the passenger side of the box....) and you'll be able to attach the valve with the correct end up. The reason I opted to have the pipes go through a u-bend was to make it so the high side and low side fittings stuck out of the plastic box in the familiar arrangement -- high side line above the low side line. Secondarily I feel this makes the airflow inside the box work better than if the lines crossed the entire width of the box to go out through the exit hole.

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Final note: Look back at post #41 in this thread. You'll see that there's a very specific length for the low-side (suction) tube that makes connection of the assembly to a custom hose easy versus nearly impossible. Specifically, this is how far the tube sticks out of the box. I'll post a graphic showing what that is so you can reproduce it if you would prefer to make your own tubes. A lot of @Dick Steinkamp 's sweat and tears went into figuring that dimension out. The reason I mention it is that even if there were OEM Toyota tubes that got the job done the odds of them ending in the exact right spot would be reeeeeally slim.
 
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Dick Steinkamp

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A lot of @Dick Steinkamp 's sweat and tears went into figuring that dimension out. The reason I mention it is that even if there were OEM Toyota tubes that got the job done the odds of them ending in the exact right spot would be reeeeeally slim.

Just to add to this, the configuration I THOUGHT I had nailed in post 41 turned out not to work when I tried to refit the glove box. David made me a suction pipe to the dimensions I provided and success!...


IMG_7393.jpg


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Also, keep in mind that my installation is in an E3. All AC parts and wiring are the same, but obviously the dashes are different and the solution as to the proper lengths of the pipes exiting the evaporator/expansion valve are probably different but with just as much precision needed.
 

Blinkling

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Yep, there it is in its victorious configuration! Thanks Dick! Y'all can see there that the defroster hoses that are the hazard to route around.

The correct amount of "stick-out" of the low-side tube (shown as Dimension A in the second image below) ended up being 3 1/2" (89mm). Dimension 'B' for the fitting I got from RockAuto (Four Seasons 18100) was 1 3/8" (35mm). I believe Dick said the one he ordered was more like 1 1/8"(26mm) but anywhere around there should be ok.

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The difficulty in making the J-shaped tube is that it's difficult to reference the outside of the box when you're cutting copper tubing to braze together. Here is the formula that ended up working:

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jjs2800cs

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I have decided to install Blinkling's system in our 2800cs which is currently all apart. But want to retain the existing copper #6 and #10 pipes that go from the evaporator thru the passenger side firewall. Yes that requires using the flare fittings. It seems everyone are trying to avoid any flare fittings in the system.

Is there a problem using them with R134a?

In the early 90's we refreshed the OEM AC system and used R12 and all the flare fittings. No leaks all those years. A little research online says properly assemble flare fitting are just fine with R134a. Maybe properly fitted is the key!!!

So we will have a combination of flare and o-ring fittings in our new system with Sanden compressor and parallel flow condenser. We are going to still use a new BMW dryer which has the flares. So are we asking for trouble here? At every flare fitting we will use the copper flared sealing washers.

I suppose one could modify the existing copper lines by cutting off the flare fittings and soldering on o-ring fittings . Anyone one do that?

Comments?

Also I used to have a Bavaria (sorry I ever sold it) and the copper lines on it were much shorted in length than the E9. Same shape just shorter.
 

HB Chris

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I still have flare on the evaporator and new steel lines from CK with o-rings everywhere else and R-134, no leaks so far. R-134 is a smaller molecule so o-rings and vapor barrier hoses are recommended but who knows for sure.
 

Blinkling

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Flare fittings are a burden when they're leaking in places difficult to reach (like inside the evaporator box or the top of the condenser). These ones we're talking about (and the ones on the drier) are out in the open and available to be tested and tightened 'till the cows come home. I don't think that using flare fittings in these particular areas is much of a liability.
 

ATL_Alan

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I'm in Atlanta so I feel your pain. I was the first guinea pig with Blinkling's evaporator last year while replacing everything in my system (I even made my own hoses) and it works great; I used R-152a (the stuff in keyboard cleaners) because I figured I'd screw up the assembly and need to vent it (I did). My system runs cool and the Sanden compressor doesn't put much drag on the engine at all. Everything I've read says expect the AC to put out vent air around 35 to 40 degrees colder than ambient air, so if it's 90 and you're getting 50 degrees or so, that's as good as it will probably get. There are charts out there showing vent temps for ambient temp and humidity for different refrigerants but I'm guessing your target chart temps will be pretty close to Atlanta (e.g. tropical jungle). This chart shows 61 degrees as the target at 90 degrees with 40% humidity but my system got down to 50 degrees driving around in the city, so it's useful more as a guide of what to expect:

ambient and humidity chart.png


My engine is out of a 1987 535 and the only issue I've had with the AC is that the engine still wants to overheat when sitting in traffic in the summer. This is with a new Ireland Engineering radiator, water pump, all new coolant hoses, thermostat, 9 blade fan, new condenser and a SPAL electric fan. I also custom made an aluminum shroud between the condenser and radiator to focus the SPAL fan through the condenser and the radiator. I crammed the largest condenser and fan that I could get in, given the engine was in place. If your engine is out, get the biggest condenser and electric fan you can; you won't regret it. If you're not a stickler for originality, get the double SPAL fan that replaces the original radiator fan. Someone else in south FL (handle RJRuiz) has that setup and says it works great. Here's his message to me:

"a pusher fan in front that works with the a/c, otherwise off.

And two 12" pullers attached to the back of the radiator, controlled by a Spal programmable electronic controller, set for fan 1 at 195' and fan two to kick in at 205'.

I removed the mechanical fan.

temp is always in the lower 1/3 -1/2 of the gauge, even when running a/c.

I purchased the aluminum fan on EBAY- it's beatifully made and substantially larger than the BMW fans. Work really well in S. Florida heat.

Sorry for the late reply!"
 
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jjs2800cs

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I'm in Atlanta so I feel your pain. I was the first guinea pig with Blinkling's evaporator last year while replacing everything in my system (I even made my own hoses) and it works great; I used R-152a (the stuff in keyboard cleaners) because I figured I'd screw up the assembly and need to vent it (I did). My system runs cool and the Sanden compressor doesn't put much drag on the engine at all. Everything I've read says expect the AC to put out vent air around 35 to 40 degrees colder than ambient air, so if it's 90 and you're getting 50 degrees or so, that's as good as it will probably get. There are charts out there showing vent temps for ambient temp and humidity for different refrigerants but I'm guessing your target chart temps will be pretty close to Atlanta (e.g. tropical jungle). This chart shows 61 degrees as the target at 90 degrees with 40% humidity but my system got down to 50 degrees driving around in the city, so it's useful more as a guide of what to expect:

View attachment 142840

My engine is out of a 1987 535 and the only issue I've had with the AC is that the engine still wants to overheat when sitting in traffic in the summer. This is with a new Ireland Engineering radiator, water pump, all new coolant hoses, thermostat, 9 blade fan, new condenser and a SPAL electric fan. I also custom made an aluminum shroud between the condenser and radiator to focus the SPAL fan through the condenser and the radiator. I crammed the largest condenser and fan that I could get in, given the engine was in place. If your engine is out, get the biggest condenser and electric fan you can; you won't regret it. If you're not a stickler for originality, get the double SPAL fan that replaces the original radiator fan. Someone else in south FL (handle RJRuiz) has that setup and says it works great. Here's his message to me:

"a pusher fan in front that works with the a/c, otherwise off.

And two 12" pullers attached to the back of the radiator, controlled by a Spal programmable electronic controller, set for fan 1 at 195' and fan two to kick in at 205'.

I removed the mechanical fan.

temp is always in the lower 1/3 -1/2 of the gauge, even when running a/c.

I purchased the aluminum fan on EBAY- it's beatifully made and substantially larger than the BMW fans. Work really well in S. Florida heat.

Sorry for the late reply!"
Thanks for the reply.

From what I have read so far it does appear to be better so I have ordered from Blinkling the evaporator setup. I have decided to stay with the two copper lines so he will install the two flare fittings on the evaporator. The other flare fittings will be on the dryer as am sticking with the stock BMW dryer. The new Sanden 508 and parallel flow radiator are o-rings. So the flare fittings are reasonably accessible if need to tighten.

Also at this time I'm stick with the stock AC fan, the earlier one with the shroud. Some say it works just fine. If I need to replace I will deal with the pain to do so.

I installed an Ireland engineering AL radiator a few years ago. With then stock AC fan, stock 5 blade engine fan and with the then stock R-12 AC system, had no problems with cooling, AC marginal but engine cooling ok. I think the AL rad really helped.

I make my own hoses, have both mechanical and hydraulic crimps, have vacuum pump, gauges, etc. So we can vacuum the system down before charging. Are sticking with for now R-134a but will research the R-152. A friend owns an AC shop that's close so if a leak develops on the 134 he can evacuate it.

I had a recent post saying how much we would like to stay with R-12, but no one anywhere near me has the equipment anymore to evacuate R-12 if there is a leak or if need to open the system for some other reason. My friend who owns the AC shop used to have the equipment but got rid of it just before we decided to restore the car!!!

Thanks and I will post performance of the AC system, but that's at least 6 to 9 months away, as the car is totally stripped and just now the shell is getting painted. I do ALL my own work (less painting) so it will take me a while to get it back on the road.

jjs2800cs
 

ATL_Alan

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I have a friend who restores antique refrigerators from the 1920's and 30's and he recommended R-152a because of the cooling, cost ($5 a can) and that it can be vented if necessary. He uses it in all his refrigerators and cars and swears by it, so if it's good enough for him, I figured it's good enough for me.

Good luck with the project, sounds like you'll be on it awhile!
 

Ohmess

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jjs2800cs

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Anyone making these modifications to their a/c should also consider adding a relay to energize the condensor fan when the coolant temp gets too high, thereby using the condensor fan as a secondary cooling mechanicm for the engine. Don and I discussed this, along with the idea of replacing the stock fan with a SPAL puller fan here: https://e9coupe.com/forum/threads/yet-nother-fan-clutch-water-pump-question.40822/post-355091
Prior to installing the Ireland engineering AL radiator, I did install a manual override switch that would turn on the AC condenser fan whether the AC was on or not. Was just a simple relay added and a switch under the dash. Used it occasionally when temps creeped up, but don't remember using it after the AL radiator.

Thanks
jjs2800cs
 

jjs2800cs

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I have a friend who restores antique refrigerators from the 1920's and 30's and he recommended R-152a because of the cooling, cost ($5 a can) and that it can be vented if necessary. He uses it in all his refrigerators and cars and swears by it, so if it's good enough for him, I figured it's good enough for me.

Good luck with the project, sounds like you'll be on it awhile!
I started to look for cans of 152, where do your find it for $5/can and how do you tap it for a charge? Does it come in cans like 134a?

Thanks
jjs2800cs
 

ATL_Alan

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I started to look for cans of 152, where do your find it for $5/can and how do you tap it for a charge? Does it come in cans like 134a?

Thanks
jjs2800cs
Lowe's or Home Depot has them; they were around $5 a can before inflation took off. I haven't checked since last summer. They're called Keyboard Duster and you use a side can tap which you can get on Amazon for about $12. Just pierce the can at the bottom and the refrigerant will flow into the low side. My system took about 2.5 cans. Screen Shot 2022-06-14 at 11.21.19 AM.png
 

Ohmess

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Prior to installing the Ireland engineering AL radiator, I did install a manual override switch that would turn on the AC condenser fan whether the AC was on or not. Was just a simple relay added and a switch under the dash. Used it occasionally when temps creeped up, but don't remember using it after the AL radiator.

Thanks
jjs2800cs
Yes, manual switch in lieu of a temperature switch is another way to do this.
 
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