OK I have read threads on using 134/152 as an alternative to R12. I currently have 134 in my system and am wondering how to optimize the cooling. Now, on a ~80 ambient day I am getting ~42 vent temps. I want to know what the temperature differential should be. I'm hoping those of you with more AC system experience can advise me.

I do have gauge sets which fit the original 12 valves and the new 134 valve adaptors. Problem is I have had trouble getting the 134 adaptors to work with my gauge set so I don't currently know the pressures. If I can get accurate high/low pressure readings, what should I target with 134? 152?

I'm thinking to add a little 134, then remove a little and compare the results. What should I be considering other than ambient temp? Is the humidity a significant factor? Hopefully I can do back to back testing but likely the tests would be conducted on different days so I need to be able to compare results during different ambient conditions.

Once I have the 134 dialed in I may try the 152 if the performance isn't satisfactory. I presume the same approach would work. Suggestions?

 

Here is a tutorial I found about 134 systems in general.

"FOR AUTO AIR CONDITIONING R134a SYSTEMS: At IDLE - Condenser inlet temp 170 to 180, Condenser Outlet temp 135 to 150 (usually a 30 to 40 degree drop in temperature across the Condenser), Evaporator Outlet temp 45 to 55, Compressor Suction temp 60 to 70 (usually a 15 to 20 degree drop in temperature from the evaporator outlet to compressor suction port). With the engine IDLING, you want to adjust the charge so the line at the Compressor suction port is about 10 to 20 degrees WARMER than the Evaporator Outlet pipe, and with the engine running at 1500 to 1800 rpm, you want the line at the Compressor suction port to be about 2 to 10 degrees WARMER than the Evaporator Outlet pipe. At 1500 RPM - Condenser inlet temp 190 to 200, Condenser Outlet temp 135 to 155 (usually a 40 to 60 degree drop in temperature across the Condenser), Evaporator Outlet temp 45 to 55, Compressor Suction temp 55 to 60 (usually a 7 to 12 degree drop in temperature from the evaporator outlet to compressor suction port).At 90 degrees ambient, for R134a systems, look for about 200- 220 Pressures on the high side and about 25-30 Pressures on the low side at idle, and at 1,500 RPM look for about 220- 230 Pressures on the high side and about 20-27 Pressures on the low side. The Compressor should cycle off at around 20 PSI."

Does this apply to our, converted systems or should I target different pressure/temperature differentials? What about our cars with a 152 charge?

 

Do not know where all those numbers came from, but to be honest they do not even look that close from my experience with a IR heat gun and gauges.

I have never seen a system run under about 250-300 PSI on the high side in 90*F nor have I seen one run 200*F at the condenser. At idle the low side pressure will be more in the 45-55 PSI range. If you are seeing 20 psi at 1,500 rpm and stationary, you are undercharged and as soon as you get on the road it is going to start cycling the compressor and you will have little to no cooling.

 

Yes, that was from a web site and is (presumed to be) generic. But it was a starting point.

I agree about the <20PSI on the low side cycling the compressor.

The last time I attempted to connect my gauge set it wouldn't "communicate" with the low side. Either a poorly designed adaptor valve or the hose connector. The 134 is a very different setup than I was used to with R12. The "catch what's in the hose" valve seems to be trouble some.

Regardless, in days past I would just put a few ounces less than specified and try to keep the low side around 30 or slightly less and add some if it was less. I'm not an AC expert but it seemed to work. With 134 combined with the gauge problem I'm just not sure if my system is working as well as it can.

With ambient in the low 80's I'm getting 42' vent temp when driving down the road. In the past with R12 I'd expect to see ~32-35' vent temp so I'm feeling it's not yet right. Or is this the best 134 can do? In leu of gauges, I thought I would try slightly different amounts of refrigerant to see if it improves.

Do you have any experience with 152? If so, what pressures/temps do you expect with it?

 

From what little experience I have, this is about right. The 134a will not match the r12, especially on just a converted system.

 

About what I would expect from R143a. You might be able to get it to cool a little better going down the highway by adjusting the cycling switch about 3/4 turn counter clockwise. Thay being said R152a cools much better in my experience. It was 96°F here and despite running a 25% underdrive crank pulley I still idle at 45°F and go down the road in the 30s in my dual evaporator Express.

 

Thanks guys, that's exactly the type of input I need. I agree, from my small amount of experience and reading all your comments, that the 134 doesn't perform like the r12. I'm really wanting to experiment with the 152. The nice thing about it is since the can will fit the R12 clamp tap, I can go back to my "good" snap on gauge set in stead of this harbor freight 134 set.

From what I have gathered I need to charge 152 at .56 the specified R12 for our vehicles by weight. Is there any other change necessary to run 152? I have a "recent" compressor and dryer and hope to drain and recharge with 152. I have a vac pump and gauges so I should be good to go.

FWIW I read that 152 was in the running to replace R12 in the first place. Both 152 and 134 are considered "non-ozone depleting" so I wonder why 134 won out. Supplier lobbying or other political?

 

From what we were told in a recent conference, r134 will be replaced in all vehicles within 5 years. Replaced with r1234a. We will see.

 

Ok here's a little more info on my current setup. I have an Air Intake Temperature sensor in front of my air filters so it reports the air temp in front of the radiator and, more importantly, the condenser. So in addition to "ambient" temps I know the actual temp at the condenser.

Anyway, on the drive home the actual ambient temp was 92'F with 50% RH.

Upon start up the vent temp was 120'F (sitting in the sun/black T-top car) the condenser temp was 115'F.
After about 5 minutes of driving the condenser temp was 107'F and the vent temp was 52"F.
I stopped and the vehicle sat for 10-15 minutes and restarted.
Condenser temp was 126'F and vent temp was 95'F.
After 5 minutes of driving condenser temp 105'F & vent temp 56'F.
After 10 minutes of driving condenser temp 97'F & vent temp 46'F.
After 20 minutes of driving condenser temp 98'F & vent temp 42'F.

From this info would you say this system is working properly considering it is retrofitted with 134A refrigerant? Still seems a little warm vent temps to me.

 

Oh great, another refrigerant to get to know lol. Interesting info though. Why do they expect to change again?

 

I goofed on the number. R1234yf, not R1234a

As far as to why the switch, the usual. Politics and environmental concerns.

http://www.shopownermag.com/relax-r1...-of-the-world/

 

I also keep seeing talk of R152a. They already sell R152a as "canned air".

 

So in my example sited above does 42' vent temp after 20 minutes of driving with 98' condenser air temp seem typical of a 134 retrofit system? Would you expect a performance gain going to 152 or should I attempt to optimize the 134?

 

I saw dramatically better cooling using R152a in a R134a system. 50/50 Propane/IsoButane is better but much more flammable.

Your results sound typical and equal to most factory new cars.

My Express van with R152a


My Titan with R152a at idle on a 107°F day. The thermister in the Titan would only allow the evaporator to get around freezing before cycling the compressor off.

 

Thanks for that reply Fast355. I just went for a ride and today is somewhat cooler with a little more humidity. With ~98' condenser temps the vent temp dipped just under 40' after about 20 minutes of driving. The only other thing I could try is to remove an ounce or two of refrigerant and see if the low side would come down any, but this is pretty much inline with what I've found with the 134. I figure for the cost of the 152 it'd be worth a try.

Now from what I have found I want to charge 152 to .56 the recommended amount of R12 and go from there. Do you know of any other changes or tips for the 152?

 

Anyone familiar with R12a? Apparently it's a propane refrigerant.

 

ES12a is for all practical purposes R-290 aka Propane. I have used both it and a 50/50 mix with R600a IsoButane.

 

Ok folks here's my update.

I recharged my system with R152a tonight. Our cars use 2.25lbs of R12 which works out to 36oz. Using the .56 conversion factor comes to 20oz of 152. Which works out great since the Dust Off comes in 10oz cans. There were a couple different brands at Wally world I chose a 3 pack of Dust Off for ~$12. BTW Difluoroethane is the ingredient we're looking for.

Anyway, I pulled a vacuum for 30 minutes or so and added 1 can with engine off. It took it right away. Started the engine and added the second can. Worked like a champ.

I was able to remove the 134 adaptors and used my old Snap on gauge set. It was so nice to have a good gauge set again and I had forgot how much I like the can tap. Here's the proof after only 7-8 minutes run time.




Previously the best temp was 39' after 20 minutes on the highway. Although this was in the heat of the day.

The real test will be tomorrow in the Alabama heat and humidity but I can tell you already that this car has never blown this cold. I had to continually wipe the windshield due to condensation on the outside. If it holds out and there are no issues this is by far the best ac mod hands down. I'm hoping a side benefit will be lower coolant temps in traffic since with lower inside temps should translate to lower condenser temps. Update soon.

 

Glad to see it seems to be working. I did some crazy insulating on my underhood components this evening. I wanted something that worked well to work even better. Bought some of the really thick foam insulation for pipes and zip ties and insulated the underhood hoses. When I have more time I am going to put the van on the rack at work and insulate the underbody hoses and exposed tubing. I also picked up a new accumulator foam insulating sleeve to help cut down on the engine heat finding its way into the a/c system.





Next I insulated the evaporator box. I bought a roll of 2" wide self stick foam tape, then a roll of the highest heat amd strongest duct tape I could find along with a roll of fiberglass insulation for pipes with am aluminum foil backing. I first removed and cleaned the box, then swabbed it down with rubbing alcohol. Then stuck the foam tape on as best as I could cover it. Then taped the edges of 6" wide stripes of fiberglass insulation and duct taped it over the box. The result turned out quite nice and really seems to have cut the heat soak into the HVAC system. With the stock uninsulated box when the compressor cycled off the temperature rose very quickly. I have not gotten to test it in the heat of the day yet, but it seems to stay much cooler. I turned the engine off in my driveway, rolled the key back and left the fan speed on the 2nd setting with the recirc option still selected. The a/c was blowing about 38*F. I timed it nearly 3 minutes before the vent temps rose to 70°F.



Next up is the rear windows are getting high heat rejection limo tint. The less heat I have to remove, the less the compressor has to work, the more it cycles and the less fuel I use. I am already running a 25% underdrive on the crank and reduced the a/c torque tables 25% across the board to keep the engine from surging when the compressor cycles. I had already reduced the about 15% prior due to the lower head pressure of R152a. A/C compressor torque values reference IAT on my Express van since GM neglected to put an A/C pressure transducer as an input to the PCM. I find it amazing the system can still pull down 40s at idle and 30s going down the road with the underdrive pulleys and dual evaporators.

 

Looks good. I need to do some more work on mine. Including hooking up the high speed fan. (Taurus fan with only low currently wired in).

Either of you know where to get a replacement seal for a side tap? Mine stuck to the last can I used and I didn't realize it. Long gone and Im having a rough time finding something that works.

 

That's not crazy to me. I think component insulation is part of optimising the system. Especially in a third gen due to three close proximity of the ac to the exhaust. Your van is probably right up on the engine too. The less heat the components absorbs the less the system must dissipate. I made a reflectiVe barrier between my unit and headers and plan to wrap the drier and some of the hoses too. When I installed carpet I used extra insulation under the carpet and behind the fire wall for the same reasons. I really have to reserve final judgement until after the next few days which are forecast to be triple digits but so far my ac is better than ever with 152.

 

Ooh that's a bummer. Mine's a snap on and probably the best place to get one is to find a SO or mac guy running round. I noticed my leaking a little last night. Probably hasn't had a can on it since the early ninetys and I was worried about it. I'd try a hard o-ring or short piece of stiff rubber hose.

Ok today at noon in ~90 ambient I'm still getting good cooling. Not 29' but better than before. Seems it pulls down a little quicker and maybe 5' lower vent temps.

I found a p/t chart for R152a and am going to put the gauges on again tonight. I've also got an IR thermometer I'm going to check. Anyone know what pressures I should look for high/low?

 

My idle suction pressure ends up in the 30-50 psi range and the discharge pressure in the 200-225 psi range. I have only swapped R134a for R152a and those systems like about 65-75% of the R134a charge. My cycling switch cuts out at about 20 psi. If you are sitting stationary and bring the engine up to 2,000 rpm you want the low side about 32-35 psi with the A/C on recirculate, the fan on high and the windows and doors closed. When you head out down the road the head pressure and suction pressure will fall and if you are undercharged the compressor will short cycle and give you poor cooling on the highway and ok cooling around town. I had to add a can to my Express last night and it was about 95°F at the condenser, high side pressure was about 220 psi, low side was about 34 psi and the air was blowing about 46°F. I only ran it about 5-10 minutes and the interior was about 120°F when I started the engine and kicked the system on. I was showing about 165°F at the condenser inlet and about 110*F at the condenser outlet. I need to mount up and wire my GMT400 truck pusher condenser fan.

 

Thanks fast, very helpful.

 

I hit the highway with 6 people, our camping gear and rafting gear in the Express. 250 miles each way. Friday night running lower blower speeds I was having issues with the front evaporator wanting to freeze up while cruising 75-80 mph. I ended up adjusting the cycling switch about 1/2 turn clockwise. On the way home cruising 85-95 mph with traffic in 96*F heat the front evaporator still froze up a couple of times (had to switch to outside vent air for a couple of minutes to thaw it out and restore airflow) with both of the blowers on high, blowing 36-40*F. I need to tweak the cycling switch another 1/4 turn or so and see what happens or perhaps let a small amount of the R152a out to lower the suction pressure and make it cycle more often. My front seat passenger was FREEZING about 20-30 minutes into the trip and had to grab a towel to cover himself with. The rest of us were badly sunburned and loving the rolling ice box. The stop he moved to the back where he was still freezing, lol.

 

Sounds like a problem a lot of us 3rd genners would like to have! My system is cooling better with R152a. Around 5 degrees vent temp but more importantly it pulls down faster so overall I'm pleased with the changeover. My high side adaptor is messed up so I haven't hooked back up since the changeover but it was running under 30psi if memory serves me.

In regard to your dialing in process;

What is the purpose of adjusting the cycling switch? I presume turning it in raises the cut off pressure?
How can I tell if my switch is adjustable? If not, do you know of a PN which will work on a 3rd gen?
How do you know it is cycling? I have not ever perceived mine to cut off. Maybe it has but I can't tell over the engine/exhaust noise. I do notice that if I get into PE (~full throttle) it cuts out and then back on. This is detectable in a data log but I've never seen it happen when not in PE.

I am under the impression that my system is not meant to cycle. Am I wrong? When it was low on 134 it would cycle very fast and erratically, it seemed something would have been damaged very quickly.

 

Turning the adjustment screw clockwise tightens the spring and raises the cutout pressure. The a/c system should cycle in cooler weather and lower cooling demands such as cloudy days or night. Your stock switch should be adjustable. It is located on the accumulator and has a round black connector covering half of it. When you remove the connector you will see the adjustment screw between the electrical terminals. I can feel when the compressor kicks in and out as well as feel the temperature difference.

 

Ok thanks Fast, I will check that out.

Now on the other hand, since I don't yet have the wonderful problem of over-cooling, what about going the other way? Would lowering the cut out pressure provide better cooling? Not trying to be silly here cause I remember on the first night I got the system charged with 152 I was getting 29' vent temps. So, likely my system isn't cycling too high but for informational purposes would there be a practical reason to lower the setting?

 

If it were cutting out the compressor before freezing the evaporator became a problem you could adjust the cutout to a lower pressure.

 

Hey Fast, I have a strange problem. This afternoon, I noticed the ac vent temp was a little higher at ~45' but seemed to be cooling well. When I stopped at the house to open my garage I notice a clicking sound. I popped the hood and the compressor clutch was cycling very rapidly. On-off on-off on-off. I turned it off a second and pulled into my garage, when I turned the ac back on the compressor was steady. Any ideas? I'm worried it will cause damage to the clutch. Please help.

 

Sounds like it is a little bit low on refrigerant. Honestly it has never hurt the clutch on anything I have messed with. Continually cycling can though.

 

Fast355 and antman89iroc, which orifice tube are you using in your setup with r152a?