AC systems designed for R12
 

This topic has probably been discussed over and over again, but I am still having some issues (very minor now) with the ac in my 201. The problem is this, if I am sitting at idle for an extended period of time say 10-15 minutes, then I will get maybe between 55°- 60°F at the vent. In a car that was made post R12 could be any make it model or year after R12, sitting in the car idling, the ac feels extremely cold. All my components for ac are new, including a brand new Denso compressor. So considering that the only major difference between pre R12 and post R12 systems aside from the refrigerant is the condenser (tube and fin vs pf) does that make that much of a difference? I am not running r134 in my car I have put in r152 and I will tell you that it is cheaper and at least 60% better. Does anyone have any recommendations on a near drop in with minimal modification for a pf condenser for a 201?

If you're sitting idle for 10-15 mins, that's going to happen in just about any car, especially if your ambient temperature is high enough. About the only thing you can do is increase the RPM's of the engine a bit to move more refrigerant and make the engine-driven fan blow a bit more air across the condenser. Mass flow of the refrigerant matters a LOT. When you're idling, you have very little mass flow, so the system can't move a huge amount of heat.

Additionally, if your car is black (I bring this up because of your signature photo), you can amplify the effect since the car's skin both absorbs and radiates additional heat into the vehicle and onto you. In a hot climate, dark colors aren't your friend in the summer. I drive a black Honda and a Midnight-blue Mercedes and it gets in the triple digits here in the summer. A/C struggles at stop lights...

Yes, the black on black in the desert during summer months has been miserable. I don't know, I do get what you are saying about mass flow, but I still feel that the system could be improved. Actually today was about 106° and this was my first time really putting the r152 to the test since I put it into the system about a week ago and I must say that it did an amazing job. Actually, I'll see how it goes in the next few weeks, but this has probably been the best the system has been since owning the car. I will keep everyone updated. I'm running the r152 with PAG150 oil it's compatible with r134 also.

I converted my 1983 W123 to an R134 system. It was done as recommended by changing all components except the condenser. I now wish I hadn't done so. It has been about 5 years. The system cools fine while underway but just does not put out well at idle as you describe. I live about 25 miles from the closest town and if I park at work on a hot day even with my windshield covered the interior just starts to feel cool by the time I get home.

I am told that a good parallel flow condenser would cure my ills. I have been looking (not very hard) for one since. If I can find one at a reasonable cost I may install. I will also talk with my local ac expert irt R152 based on your experience.

Thanks for that. This is what this forum is for.

I have seen discussion about the use of a cross-flow condenser. I have not done it yet. Just thought I'd mention it. You might want to do some research on it.

If you are idling, the condenser will not help you beyond the limitations of the system design on a hot day. You can blow all the air you want across that coil, but if enough refrigerant isn't moving through it, the system capacity is greatly reduced. Remember that the compressors in these cars are FIXED CAPACITY. They're designed to produce the correct amount of refrigerant flow when the car is cruising. If the RPM is too high and the pressure in the system climbs to a point that is outside the design limits of the system (such as when accelerating or passing), the pressure switch will cut the compressor off.

The converse is true when sitting at low engine RPMs. The expansion valve will attempt to keep the pressures elevated to maintain cooling, but it has to throttle down to do this. Your system capacity is reduced, and as a result your car heats up in hot weather.

If the A/C blows frosty when you're moving, cools the car off quickly (5 mins or so in the dead of summer) when it's been sitting out and sun-baking, and the temp rapidly drops when you get the RPM up around 1000 RPM or higher, the system is probably just at its capacity.

From everything I've read, R152A is about as close as you're going to get to R12 performance. Make sure you charge the system correctly if you're using it, you use just a bit over half the weight of R12. If your car has a "recirculate" button, use it judiciously in hot weather, it makes a big difference. My SDL will get so cold with the recirculate button pressed that you wind up adjusting the temp wheel. Of course, I haven't dealt with 106˚ temps yet. I have driven it when it was 95˚ a couple weeks ago and it did fine.

RESOLVED: Poor A/C performance resolved for systems converted from r12 to r134
 

As of now I'm considering the 9 year poor ac performance post r134a conversion, resolved. After putting in r152a my car's ac has been superb. Idling in 105*F weather for 10 minutes and getting high 30s low 40s at the vent.......when driving the temp drops dramatically. I'm using an infrared thermometer and see temps in to the 20s when cruising at 40 mph. On the freeway at extended travel time I have seen the temp drop into the negative double digits. I would definitely recommended anyone that is not satisfied with their r12 to r134 conversion to try this.

I put in r152a last weekend to give it a try, but I am not getting as good as you report. 100F today here and got 49F driving and 58F idle

How much did you put in? I put in nearly 3, 10oz cans

I put in about 26oz, at 2000rpm I have 28psi low and 350psi high

28 seems really low. My low side was about 45-50 and my high side was 300±. Although, I did bypass the gauges when I charged the system. I charged the system first and I would get in and out of the car to see what the temp felt like. If it wasn't cold enough, I would add more. Eventually it got to where I felt it was blowing cold enough. Then I would put everything back together and go drive it around. Felt cold while driving, but at a stop is was so-so. Went back and added more and that's when it was actually freezing. When I got it back I to check my pressure it was at 50± low side and 300 high side. One thing that I would recommend is try turning on your high speed fans while you're charging. Also try spraying your condenser with water while charging to get the pressures down. Then charge until it gets cold

At idle it is 55psi, high 20's at 2000rpm

My SDL is running R12, which is arguably more effective than the R152A and I'm not getting those kinds of results either. Center vent blows 40-45 once the cabin cools down and stays there. If it gets to 38, the compressor trips off and comes back on when the temp gets to 45 or so. Reading up on how the ACC system works, there's a thermostat to shut the system off at 40˚ to keep the evaporator from freezing.

Take any and all readings with a probe style thermometer, preferably one with some mass to it to even out the readings you're taking. IR guns are notoriously inaccurate with cold temperatures and with the way the A/C systems in these cars work, I'd be impressed to see a vent temp much below 35˚ in recirc mode with the fan on low.

To get a negative temperature at the vent on a 100˚ day would mean that the system has to have a >100˚ temp split which doesn't exist in any refrigeration system.

I have been using the conversion factor of 0.56 for R12 to R152A conversions. The 300E is on it now as the evap leaks. I only shot in 20oz last I recall as it holds just over 2lbs of R12 (2.1?). It did low to mid 40s last summer. 300psi on the high side is way high on 152A, even if it is 100F outside. It should have pressures very similar to R12.

One of my E23s is also on it as I wanted to see how it performed on a fresh system. Same temps as the 300E, car is black on black.

Interesting, the IR thermometer was not accurate at all in reading the cold temps. Went out today and bought a more accurate probe style thermometer and my readings are still well below 40°f. I helped a friend convert his 93 Honda civic today to r152 and his readings were in the 20s. Ambient outside temp was 93°F. Here are some of my readings taken today. I'm sure if I were on the freeway driving at speed they would be lower.

You need to make sure your temperature sensors are all in the right places. There is a "freeze stat" that cuts off the compressor when the evaporator temperature drops close to freezing to prevent ice and frost formation.

When your system is charged properly, you should be mid-high 30s at the center vent with the fan on low. Colder than that and you'll ice the evaporator up. This is an air conditioner, not a meat freezer, they operate on different principles and with different operating conditions.

Your friend's Honda only has pressure switches. If he's running that cold, you're probably off on charge. A lot. Hondas hold such small amounts of refrigerant that if you overcharge it by even an ounce you can expect to be buying him a new compressor sooner rather than later. They won't put up with it for long.

I've replaced my condenser, expansion valve and drier previously, I wonder if you can get blockages in the evaporator? The only parts of my system that are original are the AC compressor, evaportor and lines. I have all 3 of those in boxes to replace, but removing the heater box is a huge endeavor and I keep putting it off!

I wonder if somehow air is still trapped in my system? I'm using a vacuum pump down to 29mmhg...is there any way to be sure?

Use a micron gauge to ensure a good vacuum. Then charge by weight only.

Ideally, yes, charging by weight is the proper way to do it, but I would say just start charging the system and go based on what the temp feels like. When it reaches a level of coolness that you are satisfied with take it for a drive and test it out. Then check your pressures and see what you have. Way I figure, you will hit the proper or ideal charge anyways if the system is operating properly because over charge, it will feel so-so, same as with an under charge. When I charged mine to get the temps that I'm at, that is the method I used. When I went back to check the pressures I was at roughly ideal pressures on low side and high side. This is the method I used yesterday when I helped my friend do his civic....we only put in maybe a full can plus or minus. His system wasn't holding vacuum so since the 152 is so cheap and readily available we charged it anyways until we got the hissing noise of a leak....he had about 4 hardened seals that we replaced and finally no more hissing after 4 separate partial charges.

"Beer-Can-Cold" is a great way to get floodback to the compressor and trash the bearings. There's a reason you charge by weight.

If R12a is supposed to be such good stuff, why has 134a been the standard for as long as it has?

Because 134a is what's been forced down our throats after R12 was taken off the market. R152a is not marketed as a refrigerant, which is why it isn't as well known as R152a or R290a (propane). Keep your shirt on, R134a isn't long for this world either.

This is exactly right.

You guys with near 30oz of 152A in your W124s are overcharged. My 2.9lb/1300kg systems take 26oz of the air duster. The W124 is a smaller system, 20oz fills me up fully and puts up great vent temps considering I have a soiled condenser still and evap.

I used to have the conversion factor for 134A, but my computer died last year. If I can find it, I will post it.

I wanted to bump this thread and say that the r152a handles higher ambient temperatures so much better than R134a.

It was 118F today, and it was pulling 55F on the freeway, when last year in the same ambient, r134a was around 60F, so an improvement.

At idle, it jumped to 80F very quickly, but I am convinced at this point I am overcharged with oil. Once I fix some other issues, I plan to flush the entire system and put fresh oil in and see whether the pressures go down.

Glad to hear it that you finally got the r152a running through the system properly.

R152a update
 

I put the r152a in my system last year after ditching the r134. It's starting to warm up here in the Socal desert so I thought I'd just update that the r152 is still going strong. Pulling low 50's temp at vent idling ambient outside temp was ~100 (the outside temp reading is higher on the display because the car has been idling for a while in the same spot). When I take it out for some driving I'll get the temps again while rpms are up. I'm guessing I should still be pulling vent temps in the 30's....maybe even lower since its not 110*+ outside.


*UPDATED* Took car out on the Hwy today, 95* ambient temp and was pulling 30*F at the vent. It's been about a year now and considering we extreme heat as high as 120*, I'm calling this a permanent solution.

What oil is recommended for r152a?

I am running PAG oil 150. No issues for a year.
https://drive.google.com/file/d/1N0PZIJbXwYM8njGgZDFTvLhs_4iyjA_b/view?usp=drivesdk