Red Tek

[Spittybug]

I had to get some caliper seals from DMCH today and ran into Stephen. We started talking AC and he told me that for about 4 years now they have been putting Red Tek into the R-12 systems with great success. Very cold, works with old system and simple to do. I'm looking for anyone that has done it to their car and see what they think of it. I've done some researching and it seems like pretty good stuff. I know I have a slooow leak in my system somewhere, most likely schraeder valves, so a can of their leak stopper is probably in order too.

Feedback? Thanks.

[Ron]

I've had several come through the shop with Red Tec in them. It does very well, if installed in a flushed system. Two things I have against it: bad documentation and all of the pressures change, making the diagnostic charts almost useless (as would anything but R-12.) But even then it's not a big problem unless you are pushing/tweaking one for an extremely hot area.

If you do this, ignore where the docs say charge at 0 pressure and charge as liquid (if using the port at the compressor...can lock down the compressor).

[Spittybug]

I'm thinking this is a good option at this point. R134 needs new hoses, new condenser, orifice tube, compressor... to do it right. The Red Tek route looks low risk given that if it doesn't work well enough I haven't spent any other money on hardware. Stephen was really excited about it and told me how easy it was to do myself, so not like he was selling it to get me to come in and have it done. He did mention filling it very slowly for best results. Also said NOT to pull a vacuum on it; just put it in an empty system. My R-12 has all gone, so no problem there....He also said the leak stop stuff was very effective for the minor leaks I must obviously have.

I'm not sure I understood your last comment Ron??

[Ron]

The Red Tek docs say to charge at 0 pressure = no vacuum, which is what Stephen was saying. This is incorrect and Red Tek has it "slated to be removed from the documentation". Read it closely and you will see it is contradictory unless you allow air/?? into the system after pulling a vacuum, which you should never do. As Stephen said, you should add it (or any other) in slowly on a D or any other system where the low/suction port is located close to the compressor (or go to the accumulator,...). This is because liquids do not compress and it will lock down the compressor/break something.
(As I understand it, they say to use use liquid to get the intended blend... Now if you could charge liquid and were using the little cans, the amount it would be off (left in last can) wouldn't be significant.)

IMHO: AC stop leak is 1:10 at best - and that is the high dollar stuff.

[DMC-81]

Because your old refrigerant is gone, and you only have a small leak, I would definitely recommend changing the Schrader valves and as many O-rings as you are comfortable with ( i.e. The hose connections are not rusted too bad or otherwise deteriorated so that you'll risk sealing it again.), before you pull vacuum and recharge. The required parts are pretty inexpensive.

I didn't do Red Tek but I still have the original system, hoses, etc., and that's what I did. Mind you I did other refurbing work on the compressor and the accumulator, but the point is I got the 37 year old system to be tight enough to hold max vacuum all night.

If you want to go this route, I have a thread with parts and process that I can share.

[David T]

Do not use the plastic dust covers on the service (shrader) vales. Get some brass caps with "O" rings in them and just replace the shrader cores. Make sure you use cores for A/C NOT tires. As for small leaks, leak sealer is OK but it won't fix a leaky compressor seal. Not familiar with Red Tec but IMHO all of the "replacement" refrigerants are blended and do not perform as well as R-12 and have limitations on "topping off" so you cannot just add a little if some leaks out. You can still get R-12 and even though it is expensive, it is not so bad, even if you have to add a few ounces every year. It is still the best refrigerant to use in our systems.

[adam_knox]

I can't speak to maintenance of Red Tek, but i can tell you its in my car, and it is cold. Keeps me cool on humid Wisconsin afternoons. I usually have to drive with two layers for work (long sleeve shirt and undershirt) plus pants and if its properly charged it works well enough for me.

Sent from my SM-N910P using Tapatalk

[DMC1890]

I'd like to see the feedback you get. I'm also in Houston, and I'm hoping to get 1890 running again 'real soon now' after 8 years. I don't like what I read about R134 conversions. I'm considering doing the Red Tek myself, but if DMCH will do it, that's an interesting option (assuming I can survive the 20-minute drive in this heat!).

Robert

[opethmike]

I used RedTek in my former 1987 Esprit. It worked nicely.

[81dmc]

I've also talked to Stephen about Red Tek. Looks like a great R12 replacement, but it seems like a hard to find product if you ever have to recharge on the road.

I went with R134a for the ease of maintenance and low cost. My vent temps were never great on 12 to begin with, so I never lost anything. Lowest temps I've seen from vents with a knockoff SD 7H15 and a parallel condensor was around 65 Fahrenheit.:dunno:

[DMC-81]

Just in case you want to compare with R-12, I just checked my vent temperatures in this hot humid Florida summer with completely original (refurbed) equipment, and I recorded 58 degrees with an ambient temperature of 92+, and 45 degrees with an ambient temperature of 85 degrees.
Picture was taken on 08/13:
http://dmctalk.org/attachment.php?attachmentid=57777&d=1534204512

I also heard about good temperatures from RedTek. Has somebody recorded vent temperatures recently that they could share?

[Ron]

Has somebody recorded vent temperatures recently that they could share?Steve Rice was getting 42 @ 90 ambient. (http://www.dmctoday.com/showthread.php?2629-The-Red-Tek-12a-refrigerant-thread&p=62545&viewfull=1#post62545)

[DMC-81]

Steve Rice was getting 42 @ 90 ambient. (http://www.dmctoday.com/showthread.php?2629-The-Red-Tek-12a-refrigerant-thread&p=62545&viewfull=1#post62545)

That's pretty good!! Thanks for the link.

Although to compare apples to apples, my temps were recorded on Max (recirculate) mode, fan speed 2 or 3, and driving around town with a max speed of 45 mph. I'll try to get on a toll road this week and record temps in similar circumstances.

I also found that you get lower temps on lower fan speed settings... makes logical sense.

[Spittybug]

I just put on my gauges:
Ambient temp ~88*
With A/C off: Lo 45psi, Hi 55psi
With A/C on, it keeps cycling every 4 seconds: Lo 15-37, Hi 70-140 (ish)
Air vent temp sits a hair above ambient. No pipes around accumulator are cool to touch.
My Hi side schrader valve bubbles gently with soapy water. I think I last recharged this system 2-3 years ago, so it can't be a big leak.

All this makes my fan fail light flash (Bitsyncmaster's mod) even though both fans are running nicely (Toby fans). I suspect this is voltage fluctuations. I will see if I can adjust the sensitivity. When A/C is off, after about 30 seconds the fan fail stops flashing and all is good.

IIRC, I can just add RedTek without evacuating existing R12. I can try tightening the schrader with the correct tool and then do as David suggested and get an o-ringed metal cap for it. To replace it would discharge system....

Ron, you expressed concern about introducing liquid into the low side port of the compressor. I concur, but isn't that the SOP even if filling with r12? What's the alternative, just letting it gas (I've heard of putting can in hot water) or going through a long fill hose?

It looks like I'll have to get the RedTek kit with their fill hose/gauge. It needs the can piercing valve/fitting and the other end has to fit the r12 port on our compressor.

[DMC1890]

The way I read the Red Tek info is that you can mix with the remaining R12, but that it would be best to remove the R12. Then it seems unclear as to whether it would be best to pull a vacuum on the system. One bit said don't charge into the vacuum - which sounds silly. What are you supposed to do then - suck atmospheric air back into the system first?

When are you doing this? I'm anxiously waiting to hear your results. I actually got 1890 to go around the block a couple of times yesterday afternoon for the first time in a long time, but as you know it was hot. I probably won't try the Red Tek myself until I replace the tires, which are old enough to vote.

[David T]

I don't know about this stuff. I just went on the website and read a lot of conflicting info. It says it isn't an HC then it says it is classified as one. Says it has the characteristics of Propane and Butane but isn't. Says it is a"blended" refrigerant. Says to add to an R-12 system then says don't mix refrigerants. Says not to add to a hard vacuum but how do you do that if you pull the R-12 out and don't want to mix refrigerants? Says it has a lower density than R-12 yet claims better performance than R-12. That doesn't make any sense if you know anything about thermodynamics. There is no info about "topping off" but if it is a blended refrigerant you can only "top off" once or twice at most. There are a lot of R-12 substitutes that claim to be "drop in". I have yet to see any that are as good as R-12. I am skeptical of their claims until proven otherwise. As long as you can still get R-12 why would you mess around with this stuff?

[Bitsyncmaster]

Propane (R290) is going to take over as a refrigerant because of all the EPA restrictions on everything. Your even allowed to vent to the air propane from a system. Propane was used in early years and only stopped because the new refrigerants were not flammable. There is a 150 gram limit on charge now which is why big systems don't all use it now.

[Ron]

To replace it would discharge system....
Not if you use one of these:
57880
(https://www.amazon.com/MASTERCOOL-91490-Standard-Remover-Installer/dp/B000O823Z8)(Search for a less expensive model)
(https://www.amazon.com/MASTERCOOL-91490-Standard-Remover-Installer/dp/B000O823Z8)

Ron, you expressed concern about introducing liquid into the low side port of the compressor. I concur, but isn't that the SOP even if filling with r12? What's the alternative, just letting it gas (I've heard of putting can in hot water) or going through a long fill hose?
SOP is gas for a D/R12 (upright), through a manifold. Unlike when using a small "can", the refrigerant has time to expand while it travels through hose>manifold>gauge>hose.
If you must use liquid, as I said above, you could charge it at the accumulator, via the low pressure switch port if necessary. Hopefully someone hasn't removed the valve there -- Be careful. This is where I would charge any blend calling for liquid from a jug (to ensure it actually gets a blend,which is why they call for liquid...). The import things here are to not let liquid into the compressor and let the correct blend out of the container.

Hot water is sometimes used to raise the can temp/pressure, which helps speed up the charging process (gas/liquid). (Cold/impatient;-)


It looks like I'll have to get the RedTek kit with their fill hose/gauge. It needs the can piercing valve/fitting and the other end has to fit the r12 port on our compressor.Better to connect the adapter to the center tap of the manifold.... Works for all of the above, not to mention you can watch the pressures easier.

[David T]

Cheaper tools won't have that valve that allows you to withdraw the core, close the valve undo the tool, R & R the core, and then put the core back in. You are correct, to fill using a blended refrigerant you are supposed to fill it with liquid so you don't "unblend" or separate the components. If you try filling with the gas some of the parts of the blend will vaporize at lower temps and pressures so you won't get the right mixture into the system. I like to pull a hard vacuum and get as much liquid in as I can without running the compressor. I finish off by putting in the little bit necessary by liquid slowly so I don't feed raw liquid into the compressor. When you fill with liquid the can doesn't get cold. It is only when you try filling with the gas that the can will get very cold because you are vaporizing the liquid in the can and that cools the remaining liquid which is why you would use hot water to keep the can warm. Since you are only putting in 2.2 lbs you should be able to get most of it in as liquid without even running the compressor. As for how to hook up, SOP is to hook up the blue low pressure hose to the suction port at the compressor, the red, high pressure hose to the discharge port of the compressor (it SHOULD be at the discharge of the condenser coil but there is no service port there) the yellow hose to the charging cylinder or can, and if you have a 4 handed manifold, the black hose to the vacuum pump. Otherwise you must move the yellow hose from the vacuum pump to the can. The method can vary if you have a recycler. For everyone changing the refrigerant, you are supposed to put a label conspicuously showing the type of refrigerant and the amount. Depending on what you put in you must also put adapters on so you can't easily mix up different refrigerants. Mixing refrigerants is VERY BAD. It makes what you have in your system unrecoverable and unrecyclable. When doing a major service the amount of oil in the compressor should be checked and added to if necessary. On a leaky system you can lose a lot of oil because no one ever adds any, they just shoot some gas in. Oil leaks out along with the gas. Over time you can become very low on oil. Without enough oil the compressor will not live long.

[hippieman9]

I have Red Tek In my Delorean, and it is Ice Cold. The PO had it converted by DMC CA 5 or so years ago. I had to recharge it this summer, (it had been 5 years since it was serviced last) But it works great! Bought the kit on Amazon.

[Ron]

Cheaper tools won't have that valve that allows you to withdraw the core, close the valve undo the tool
Sure they do:
57883 (https://www.ebay.com/i/202293148459?chn=ps)
$19.99 Free Shipping. That's 43% less. Fits R-12 and 134a to boot. (https://www.ebay.com/i/202293148459?chn=ps)

[David T]

Sure they do:
57883 (https://www.ebay.com/i/202293148459?chn=ps)
$19.99 Free Shipping. That's 43% less. Fits R-12 and 134a to boot. (https://www.ebay.com/i/202293148459?chn=ps)

I guess so! It is not so much that they fit a particular refrigerant, they have to fit the 1/4 flare fitting. Buy a pack of cores too. And caps.

[Spittybug]

Agreed, I'm not seeing how they attach to an R12 fitting that is a screw on. I can only see how it attaches to a 134 quick connect....

[Ron]

I guess so! It is not so much that they fit a particular refrigerant, they have to fit the 1/4 flare fitting. Buy a pack of cores too. And caps.
R-12 is 1/4" flair.


Agreed, I'm not seeing how they attach to an R12 fitting that is a screw on. I can only see how it attaches to a 134 quick connect.... Looking at the other pics in the link, I'd guess you remove the the 134a section...

EDIT: Maybe a set of these (https://www.google.com/imgres?imgurl=https%3A%2F%2Fsc02.alicdn.com%2Fkf%2 FHTB1BSJUPVXXXXbaapXXq6xXFXXXl.jpg&imgrefurl=http%3A%2F%2Fguide.alibaba.com%2Fshoppin g-guides%2Fr12-retrofit-r134a.html&docid=NfS1iSJPET6yDM&tbnid=lnTK0y0ptKPELM%3A&vet=10ahUKEwj73I6G6YHdAhUkTd8KHVjEC_oQMwjrAShLMEs. .i&w=500&h=294&bih=663&biw=1396&q=Retrofit%20R12%20to%20Accept%20R134a&ved=0ahUKEwj73I6G6YHdAhUkTd8KHVjEC_oQMwjrAShLMEs&iact=mrc&uact=8) are under the caps:
57892
...looking at it again, I wouldn't bet on it regardless of what the ad says...

[Now you know why I suggested you search :deviltail:]

[hippieman9]

They give you a low side adapter in the Red Tek kit.

[Nicholas R]

Just to add something to this thread regarding install pressure.

I called Red Tek and spoke to their technical department, because I felt their instructions were vague.

Red Tek explicit told me that, YES you should pull a vacuum on your system prior to installing their product. They told me to vacuum it down to ~29inhg, but not to go any farther. (not sure how you could go much farther since 30inhg is pretty much a perfect vacuum). Regardless, I in this thread where it was mentioned that you want to install this at 0psi (gauge pressure), meaning there will be air in the system. Red Tek explicitly told me you do not want air in the system if you can avoid it.

Sarah and James at DMCH recommended Red Tek to me at the Celebration Car Show as well and they also indicated that DMCH installs Red Tek after vacuuming down a system as normal. It was this discussion with them that led me to investigate Red Tek as well. I've got several more cans in my garage and am considering another go with it.

Just my $.02

Red Tek's instructions are not clear on this matter and I believe they need to reword them. Based on Ron's comment, hopefully they'll update the instructions. Regardless, their instructions are what led me to reach out to them.


As long as you can still get R-12 why would you mess around with this stuff?
Because it's significantly cheaper (~$25 for a full charge), easy to buy (amazon, ebay, or direct), legal to vent, doesn't require a license to buy or service, compatible with all lubricants, and can be easily installed in one's garage. Is this enough reasons?

[David T]

The only thing left to say is, does it work as good as R-12? The difference in price is not going to break anyone's piggy bank. The only reason I can see for using a cheap refrigerant is if you are trying to keep a leaky system going by constantly topping it off. Then you're right, R-12 gets expensive. And while we are talking about "topping off" or regularly adding refrigerant because it is leaking out, none of the blended refrigerants allow for constant topping off. It throws the mixture of the blend off. Ask Red Tek about that. Their literature says it is less dense than R-12. That would imply it has a lower molecular weight which means smaller molecules. Smaller molecules means it leaks more. The Delorean has very long hoses. Hoses have leak ratings per foot of length. All that hose adds up to more leakage which is why the hoses should be replaced with "barrier" type hoses which have a lower leak rate. A good idea no matter what refrigerant you use. No one should be running on the original hoses, they are WAY past their deign service life. I am not against using Red Tek but I am skeptical of all of these blended refrigerants. IMHO if you are not going to use R-12 then do a full conversion to -134. That means flushing the system of all of the old oil, changing the service ports, hoses, dryer/accumulator and maybe going to the variable orifice. Unless you pull a "hard" vacuum like at least 400 microns, you will be leaving air and moisture in the system.

[DMC-81]

No one should be running on the original hoses, they are WAY past their deign service life.


...and yet, in my case, replacing seals and valves netted a tight system that held 30 in. hg of vacuum not for 30 minutes, but all night. This was with original hoses, etc. The system has been holding up well in one of the country's warmest climates. In my opinion, it depends on the condition of the hoses and fittings, and it is up to the owner of the car to decide.

Here's DMCMW's feedback on common causes of leaks. No mention of age related failure as a frequent cause:
http://dmctalk.org/showthread.php?12090-Air-conditioning-hose-replacement&p=175680&viewfull=1#post175680

Thinking about it, the original hoses have soaked up the refrigerant oil for 37 years, helping to seal them internally, and I'm sure they used a different rubber compound than today's products that are generally designed for obsolescence within 7 years.

37 year old tires? No, it's not worth the risk. 37 year old AC hoses in good condition? I say, knock yourself out!

[David T]

Holding a vacuum is no big deal. All you are holding against is about 15 psi negative. To test the system common practice is to put in Nitrogen to about 150-200 psi. Several big benefits to doing it that way. Not only will you know if there are leaks but you can find them by using bubbles. You can find very small leaks. You don't suck any air, moisture or dirt into the system. You provide a "sweep charge" that you remove, further diluting and removing any traces of air or moisture. No one is saying you MUST replace your hoses but just understand that they were not meant to last this long. If you are thinking about using -134, keep in mind the system will be running at even higher temperatures and pressures than with R-12. Are you sure you want to do that on old hoses?

[DMC-81]

Holding a vacuum is no big deal. All you are holding against is about 15 psi negative. To test the system common practice is to put in Nitrogen to about 150-200 psi. Several big benefits to doing it that way. Not only will you know if there are leaks but you can find them by using bubbles. You can find very small leaks. You don't suck any air, moisture or dirt into the system. You provide a "sweep charge" that you remove, further diluting and removing any traces of air or moisture. No one is saying you MUST replace your hoses but just understand that they were not meant to last this long. If you are thinking about using -134, keep in mind the system will be running at even higher temperatures and pressures than with R-12. Are you sure you want to do that on old hoses?

David, we've been through this exchange before. YOU just said in your last post that "no one should be running", so perhaps you should change the wording of whatever you cut and paste in A/C threads to be a little less condescending.

By the way, I checked several quality A/C shops around here and they don't use a Nitrogen charge. Holding vacuum is the primary test for leaks on an evacuated system, and prepares the system for charging, so around here, it is a big deal. IMO, the time to check for leaks when you suspect one is while the system is still charged and operating using leak detection dye, etc. That is the common practice here.

No, I'm not thinking about converting to R-134 for several reasons, including higher pressures, hence my decision to stay with the original hoses.

Once again, my point is, it's up to the owner what they want for their car, so you shouldn't make blanket statements like this:


No one should be running on the original hoses, they are WAY past their deign service life.


Anyway, back to RedTek....

[David T]

Using Nitrogen is an extra, time consuming step and added expense so many shops just skip it. It is especially necessary to do on a "dead" system because, as you say, you can't test it if it isn't charged. I stand by my words of no one should still be using 30 year old A/C hoses. Check with your local shops and see what they say about that. I like using Nitrogen because it allows you to pressurize the low side to a higher pressure so you can find the smaller leaks. Under normal use the low side never gets above 70-80 psi and that is only when the system isn't running. I also pull a harder vacuum than most shops who vacuum til the gauge stops moving and then shoot the refrigerant in. I get to at least 400 microns and I hold it for at least an hour so I KNOW there is no moisture left in the system. All of this takes time, time most shops don't want to spend. Because if they did they would have to charge the customer a lot more.

[Bitsyncmaster]

I get to at least 400 microns and I hold it for at least an hour so I KNOW there is no moisture left in the system. All of this takes time, time most shops don't want to spend. Because if they did they would have to charge the customer a lot more.

Can you post a photo of your vacuum pump and micron gauge? I'd like to know what works for you to get that good vacuum. Also do you own a nitrogen tank or rent it?

[DMC1890]

Red Tek sounds like the way to go for me. I'll report back in a few days after I've done it. I read an interesting perspective on 134 on Hagerty's web site, saying that many European/Japanese cars from the 70s/80s had A/C that was already marginal on R12 (they don't have Houston's climate to deal with!), and that 134 just makes matters worse.

I'll take my chances on the old hoses, but...



37 year old tires? No, it's not worth the risk. 37 year old AC hoses in good condition? I say, knock yourself out!

My tires are old enough to vote - and new ones are on order.

[DMC-81]

Using Nitrogen is an extra, time consuming step and added expense so many shops just skip it. It is especially necessary to do on a "dead" system because, as you say, you can't test it if it isn't charged. I stand by my words of no one should still be using 30 year old A/C hoses. Check with your local shops and see what they say about that. I like using Nitrogen because it allows you to pressurize the low side to a higher pressure so you can find the smaller leaks. Under normal use the low side never gets above 70-80 psi and that is only when the system isn't running. I also pull a harder vacuum than most shops who vacuum til the gauge stops moving and then shoot the refrigerant in. I get to at least 400 microns and I hold it for at least an hour so I KNOW there is no moisture left in the system. All of this takes time, time most shops don't want to spend. Because if they did they would have to charge the customer a lot more.

David, none of the upscale shops I visited even had equipment for a nitrogen charge. It's not like it was an extra charge service. Perhaps it is common where you are, but not here. If you like it, that's great. IMO I think that charging the low pressure hose to twice operating pressure is inviting leaks where none existed before.

Can you clarify "400 microns"? Because 400 microns of mercury = 0.02 inches of mercury (inHg) and even 400,000 microns of mercury = 15.75 inches of mercury. You would need 762,000 microns of mercury to equate to 30 inches of mercury which is max vacuum on my newish gauge.
I have asked shops about the hoses, keeping in mind my goals for my car... originality. They basically said if they are not leaking and in good condition, and you are staying with R12, then keep the original hoses if you want.

[David T]

The "equipment" to pressurize with Nitrogen consists of a tank and a pressure regulator. You have to buy the 1st tank and from then on you just exchange when empty for a full one. You also have to buy the regulator. The tank costs about $22 to refill and lasts for about a dozen cars, less when you use it on larger systems like a house central A/C system. My vacuum pump is a RobinAir model 15101-A and my vacuum gauge is a Supco Model VG-61. You cannot measure a hard vacuum with a compound gauge, not accurately anyway. I can actually see when I have the moisture out by the way the vacuum decreases if I shut the valves to the vacuum pump and watch the system vacuum. You can also use Helium for even smaller leak detection but Helium is more expensive but then you can also use it to blow up balloons. If you are interested in this kind of stuff you should go to a local supply house that services the A/C tradesmen and talk to the counter guys and they will hook you up with what you need.

[hippieman9]

The only thing left to say is, does it work as good as R-12?
.

I have been running Red Tek in North Carolina this summer with 80-90 degree weather and it is ICE cold in the car. No complaints what so ever. I spoke to Red Tek as well and they don't list the product as being compatible with R12 because R12 is illegal to sell. So they only list it as a replacement for R134a. But It does work and work well. No issues here!

[Spittybug]

I have been running Red Tek in North Carolina this summer with 80-90 degree weather and it is ICE cold in the car. No complaints what so ever. I spoke to Red Tek as well and they don't list the product as being compatible with R12 because R12 is illegal to sell. So they only list it as a replacement for R134a. But It does work and work well. No issues here!

Did you evacuate the R12 and pull a vacuum, or did you just add the Red Tek in?

[hippieman9]

Did you evacuate the R12 and pull a vacuum, or did you just add the Red Tek in?

My car was converted to Red Tek by DMC CA a couple of years ago. When I purchased it this past March and the A/C was not blowing cold, I just recharged it with a can of Red TEk and its perfect.

[DMC1890]

Did you evacuate the R12 and pull a vacuum, or did you just add the Red Tek in?
I did this yesterday. I still had a small amount of pressure (R12) in the system (~1 Bar), even after at least 8 years of non-use. I thought it would be best to evacuate and pull a vacuum so that I would know that the system would then contain only Red Tek.

The kit I bought included a hose/gauge, can of leak stop, and 2 cans of refrigerant. The hose has a R134 fitting, and the kit did not include an R12 adapter, which Red Tek sells separately. I used my old gauge set which has native R12 fittings.

The leak stop, plus the 2 cans of refrigerant matches almost exactly the equivalent of the 2.5 lbs of R12 that is specified for the D.

I ended up with the following results:
Ambient temp 90 deg F
Engine idling at 850 RPM
Blower on speed 4, recirc 'off'
Low side pressure - 40 psig, High side - 160 psig
Outlet temp - 64 deg F

Static pressure - 67 psig (low and high)

I may be slightly low on the charge, based on the measured pressures, but I didn't want to tap another can just yet. I assume that at driving speeds, and at lower blower speeds, and on recirc, that I will have lower outlet temps. I still don't have current TX state inspection and registration, so I've kept a low profile on the streets.

[Morpheus]

The proper charge amount of RedTek for the DeLorean is 11oz. You have way too much in the system.

The Leak Stop can contains 2 oz of RedTek and 4 oz leak stop. One can of RedTek is 6oz. If you put in both cans of Red Tek and the Leak Stop, you have 14 oz of RedTek in your system.

[DMC1890]

Thanks Brandon. Perhaps I made some mistakes here. I'm basing my determination on page N:07:01, which gives the total R12 charge as 2.5 lbs. Then I'm using the Red Tek weight equivalent chart:
57961
This give me a Red Tek weight of between 13 and 14 oz.

Possibly the R12 capacity is actually only 2 lbs?

[Morpheus]

The R12 charge was reduced to 2.2lbs in one of the service bulletins, I can't remember which one at the moment.

Edit:
Nevermind, found it.
http://www.dmcnews.com/bulletins/ST-29-11.81.html

[DMC1890]

Well, that just confuses things even more! First, it says the previous spec was 2.75 lbs (not the 2.5 lbs in the manual), but then it also says that the spec is being changed with VIN 4080. So, does that mean that compressor and other component changes at >4080 prompted the update, or that it applies to all, including previous VINs. BTW, mine is 1890.

So, I called DMCH, and they say that the Red Tek charge should be 11 oz, regardless of the previous R12 charge spec. And, the only reliable way to get the right charge is to vacuum it back down and start over.

[DMC-Ron]

Well, that just confuses things even more! First, it says the previous spec was 2.75 lbs (not the 2.5 lbs in the manual), but then it also says that the spec is being changed with VIN 4080. So, does that mean that compressor and other component changes at >4080 prompted the update, or that it applies to all, including previous VINs. BTW, mine is 1890.

So, I called DMCH, and they say that the Red Tek charge should be 11 oz, regardless of the previous R12 charge spec. And, the only reliable way to get the right charge is to vacuum it back down and start over.

There seems to be a dependency in the R12 charge. As you note the Workshop Manual lists 2.5 lbs. (N:07:01) However, the DMC Technical Manual lists 2 lb. 12 oz (2.75 lbs.) on page 139. Perhaps the Technical Manual is including the oil?

Ron

[Ron]

$.02

The reason the charge was changed is because some compressors were knocking when starting the engine with the AC on. IF yours does/did this, then you would use 2.2 lbs R12. Converting R12 to 134a calls for a 10% reduction in the charge (because of higher pressures etc). So, you would use 2.0 lbs 134a. Which means you would use 12 oz = 2 cans Red Tek 12a, according to their chart.

Note:
2.75 lbs R12 => 2.475 lbs 134a => 14.85 oz Red Tek 12a
2.50 lbs R12 => 2.250 lbs 134a => 13.50 oz Red Tek 12a
2.20 lbs R12 => 2.000 lbs 134a => 12.00 oz Red Tek 12a

So, 14 oz RedTek may be too much (if yours knocks), but probably not the problem.
I would guess replacing the cycle switch with one that cuts out at 25-32 psi (as per WSM, N:09:01) instead of 40 psi would be the next step. Then confirm that the high side pressure falls within the given range when the clutch cycles out -- If it's high/knocks, reduce the charge...
Double check on a very hot day!

[David T]

If you put the correct amount of refrigerant in and it isn't cycling the way it should (assuming everything else is perfect, clean coils, etc) the low pressure switch CAN be adjusted by turning the screw in between the two electrical terminals. Ron is correct, under some unusual conditions you can get knocking so DMC's 'fix" was to reduce the amount of refrigerant but that reduces the A/C's cooling capacity. Refer to St-29-11/81 where the charge was reduced from 2.75 lbs to 2.2 lbs if knocking noises are observed during starting with the A/C on!. You can take that to mean always use 2.2 lbs or use 2.75 if you can as long as you don't hear knocking. Regular and consistent knocking will damage the internals of the compressor so you don't want to do that. DMC reduced the factory charge to 2.2 lbs after vin 4080. The label on the compressor says 2.5 lbs.

[Ron]

...His is ~30% off, so if it was factory set, I'd pitch it.
(Old switches are often flaky after adjusting them anyway....Random -5 to +10.)

[DMC-81]

After the comments of RedTek being flammable, I thought I'd share this warning about R134-a that was on the instructions for the OEM spec AC compressor for my daily driver. I had a chuckle about this.

58006

I guess I'll have to be extra careful when I swap this out! :hihi2:

[David T]

While R-12 isn't flammable, if you oxidize it in a flame you create Phosgene gas. Very deadly. Propane is a VERY good refrigerant too but it is also flammable.

[lazabby]

When using Redrek, what should be the high and low pressures on the gauges?

[DMC1890]

I did get this from Delorean several years ago, when they said they were actually using Red Tek in their shop. I don't know if that's still the case.

[JohnnyK]

Propane is a VERY good refrigerant too but it is also flammable.

I believe Redtek 12a is just propane (or a similar hydrocarbon). Since you need a license for r134a in Canada, Redtek 12a is just what all the parts stores sell (whereas in the US, you can just buy 12oz cans of r134a).

[Bitsyncmaster]

Propane is a three-carbon alkane gas (C3H8

From the Red Tek safety data sheet.

Alkanes 100%

There are no additional ingredients present which, within the current knowledge of the supplier and in the concentrations applicable, are classified as hazardous to health or the environment and hence require reporting in this section.

[David T]

If Redteck is Propane (or even it it only contains a small amount), it is illegal for use in mobile equipment in the US. In California a lot of people who were having problems with their A/C in their leased cars went to Mexico where they got them fixed cheap (they filled them with Propane!). So many did it that the dealers all got refrigerant testers to check for Propane when people turned the cars in. Propane is a great refrigerant but it is extremely flammable. Many years ago a house trailer with propane tanks caught fire in the Holland Tunnel (it connects NY & NJ under the Hudson River). The fire was so intense it was difficult to put out once the Propane tanks were involved. Every since then trailers with propane tanks are expressly forbidden in all of the tunnels. Most house trailers have 2 30 lb tanks, a car would only have a couple of pounds but it is still very dangerous because it is heavier than air and goes into the storm drains where not only will it burn, it can explode. We just saw the most recent example of this in Philadelphia under I-95. It was gasoline and the fire was so intense it weakened the steel understructure of the overpass causing it to collapse. If you look close at the videos you can see fire coming out of all of the nearby storm drains. All of the underground utilities in the area were also damaged. R-12 is still available on E-bay and a couple of pounds of it is not all that expensive. If you still won't use R-12, R-414a is a viable drop-in replacement. It is a blended refrigerant and won't work as well as R-12 but it works better than R-134.

[Ron]

From redtek.com (https://redtek.com/12a/#:~:text=Although%20RED%20TEK%2012a%20is,family%20 as%20propane%20and%20butane.):
"Although RED TEK 12a is developed to give similar operating conditions and capacities as R12 and R134a, this product is an Alkane / Hydrocarbon and comes from the same hydrocarbon family as propane and butane."