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Rebuilt the climate control system. New foam and everything. Cleaned out the evaporator core and condenser. All looks great, albeit a little dirty.
Rented a vacuum pump and gauges from O'Reilly's. Pulled a vacuum on the system. No leaks, but it only got down to 28-29 in/hg. Ran the pump for another 45 minutes to try to get as much moisture out as possible.
All is going well. Put the first 10 ounce can of r152a in and I'm almost instantly getting 40 degrees at the center vents on low fan speed. Low side pressure is reading 71 psi. High side is reading 70. Idle speed has to come up to at least 1500rpm to keep from stalling with the compressor running (around 900 rpm with compressor on.) Seems like a lot more load than it should be. Especially when I've seen people recommend 100 rpm gain to compensate.
System stabilizes, next can goes in, and I'm getting 55+ degrees at center vents. That doesn't seem right. Low side is reading 30 psi and high side is reading 165 psi after running for a bit. Pull low side hose from system and cap the port.
Let the system cool down and come back in 20 minutes to pull the high side hose off the system. Still reading about 150 psi on hot side. Hardly went down at all after letting it cool. Nowhere near the recommended 60-80psi.
Took it for a drive and the AC blows almost uncomfortably cold for the first 15 minutes, but on the way back it definitely wasn't. I didn't think to bring a thermometer on the drive.
Did I make a noob mistake and overcharge the system somehow?
Did you replace the TXV while you had the evaporator out? Did you flush the system out? I'm not sure if there is enough information to pinpoint anything at the moment.
Make sure the evaporator isn't frosting. Get some temperatures of various locations and report back. I'll compare your temperatures with what I have. That said, I finished my install on the 22nd to only have it lose the refrigerant by the following weekend. I have found the leak and hopefully it's now good. Luckily we are using r152a so the environment is fine.
Went and ran the ac again. All data related to low fan speed. Got 50 degrees at idle at the center vents and 44 degrees at 2k rpm at center vents. At around 2k rpm there is a rhythmic surging sound that increases in frequency with rpm. Above 3k rpm I can't hear/feel it anymore because of the engine noise.
Took the car for a short drive and it held at 45~ degrees for a while then it warmed up all the way to 61 degrees at the vents. Held around that temp for a while and then the temps climbed back down to 45. It took a long time to kick back on and start cooling again. I am comparing it to a late model AC system though, so this could just be how 40-year-old AC technology acts. Got back home and was reading 52 degrees at idle.
You are supposed to fill with the fan on high. I suspect this is to make sure it cools under heavy load. Your temps fluctuating may be the freeze switch located up by the center vents turning off the compressor. Thats by design BTW. The load from the compressor shouldn't bog the engine that much that it needs to be at 1500 rpm to survive the cycling. Not sure whats up there.
I am in the middle of writing my own AC reinstall up for my SA but I will say it leaked out over the last few weeks sitting, so I have a leak to find. That said when I first got it done it showed pressures low and high similar to what you stated. The ambient air temp makes a difference as well. One rule of thumb for high is that it should be around 2X ambient.
These systems are fairly primitive compared to cars today. They cycle much slower and also have more drag.
Fill with fan on high? Should I redo with the fan on high?
Would the belt being too tight maybe causing too much load?
At this point I wouldn't refill unless you just want to practice doing it. LOL I'm not sure what the logic for fan on high is but I suspect its to make sure the entire system is activated when filling. Like, a best practice that helps make sure the process works for a lot of different car makes. It may have to do with making sure the resistor pack is bypassed (which happens when you put the fan on high) and doesn't add heat to the system.
I almost suggested the belt was too tight but thought, nah its probably ok. Belts are tight enough if they deflect no more than about 1/2 in when pushed down with your thumb hard.
Not dismissing the prescribed procedure, but the fan speed has no mechanical connection to what the compressor is doing. Fan on high or low shouldn't matter for fill purposes.
Sounds like you have a shoddy compressor. If the AC "on" causes that much drag, there's something mechanically wrong. Too tight of belt should show as drag all the time. When you turn the AC on the compressors clutch is activated and the load of the compressor is introduced. If that in itself drags the motor down to stall-rpm's, your compressor is bad. Or some part of your compressor (clutch, wiring, ....something).
Not dismissing the prescribed procedure, but the fan speed has no mechanical connection to what the compressor is doing. Fan on high or low shouldn't matter for fill purposes.
It does cause the highest cooling load by pushing the most air across the evaporator, so in some sense it may affect a marginal compressor.
BTW, if that compressor has that much drag, something is up for sure. Normal compressor load is only going to affect rpms in most cars by maybe 1-200 rpm.
Finally, many months later, Texas summer is on its way so I figured I'd better get my AC going again. The third or fourth time I used my AC after these previous posts, my high side hose out of the compressor failed.
Restarted entirely, new hoses all the way around remade at my local CarQuest, new fittings everything: 187 dollars. Not bad.
The compressor from RockAuto is an exact replica of the factory one I had. Flare fittings, everything. Did have to drain the oil it came with and replace it with ester, but that's no issue. To get a warranty on the compressor, I had to replace all of this stuff, and the AC/Expansion valve, and use ac flush on the parts that didn't get replaced, which was only the evaporator and condenser.
New drier, of course, the system had been open for many months. RockAuto no longer has the flare-fitting drier for sale. Fortunately, it is a universal drier from Cold Hose. https://coldhose.com/collections/rec...36098003533984
Charging went well, had some loose fittings that tightened up nicely and held a vacuum.
Unfortunately, it's still killing my engine at idle when it kicks on. I'm idling at around 900-1k. E-fan kicks on and it drops to 750 or so. The compressor comes on and it will die if I leave it alone. If I pull the choke out enough to get a fast idle at around 1400, it will do just fine. Only enough to engage the fast idle. Except the choke doesn't stay out like that, so I have to pull it back out every time I try to stop. I could maybe tune my idle up a bit higher and see how it does. I'm not too worried about this part.
What I am worried about is that sometimes the compressor kicks off long enough for the fan to blow warm air and the cabin to get uncomfortable. I say sometimes, but it really feels like the compressor is off more than it's on. Even does it at highway speed. I'm thinking there's some electrical funkiness going on. Because everything else should be solid. Maybe the AC thermostat switch mounted on the evaporator is doing some weird stuff. The switch IS dated August 1979, so...
I found this which is the closest thing I could find to the original part number of A46-3111-00: A46-3111-030
When you turn on the AC, the idle compensator is supposed to bring the RPMs up to keep the compressor from stalling the engine. When you press the AC button, you should hear a click (the ac clutch engaging) and then the idle increases, to something like 1200. It's the AC solenoid, white vacuum circuit, you can fiddle with the screw on the top of the diaphragm there in the blue circle.
If that's all working, then I wonder if your system is overcharged? How much R152a did you put in the system. Folks here suggest about 2 10 Oz cans. I calculated the R134a charge to be 28.8 Oz based ont eh oem R12 weight and a factor I found on the Internet and can't remember. I figured the Sanden compressor to take about 5 Oz. of oil. I used R152a and Ester. If it's overcharged you can get liquid at the low side of the pump and that can overwork it. If you hear the pump clattering, that's not good.
Part of the issue, I would imagine, is that I do not have any rats nest, so no idle compensator or even the provisions to mount one as my carb is very likely pre rx7. Think rx3 or something similar. I should probably get an actual rx7 carb, but without a rats nest would there even be a way to use the idle compensator?
I put 2 10 ounce cans in the system, the paperwork with the compressor said that it holds 3 oz of oil, and all the information I can find on this forum says to add another 3 oz to the drier as well. I don't think I'm overcharged, when the system blows cold, it blows about 38 degrees out of the center vent. I don't think it would get that cold if it were overcharged.
I think your stalling issue is because you don't have an AC idle compensator. Mine was poorly adjusted and it would stall when I put on the AC. These 12A's are tiny! Maybe you can wire in a solenoid of your own that moves throttle a bit when the AC clutch kicks on...that's exactly what the vacuum diaphragm does anyway.
Can you put an voltmeter on your ac temp gauge to see what it's doing? I don't know how those work.
There's this box, which I believe is called the AC compressor relay, which outputs to the compressor and activates the clutch. The blue wire, I believe, goes to the ac button on the fan speed switch. The yellow wire is to the thermostat on the evaporator. I am not sure where the red wire goes. I know one of the black wires is the output to the compressor.
What I'm mostly wondering about is the empty pin below the black wires. Any ideas? Unfortunately there's no wiring diagrams for this in my haynes manual, likely because this is dealer ac. (At least, I couldn't find anything.)
FWIW, the two problems you have are dying at idle: your electric fan makes the alternator work harder, and the AC compressor stalls it. The fix would be some idle compensation.
The trickier thing is the cycling on/off on the highway. It sure sounds like your temperature switch is worth testing
For that relay you show, out of my depth on this, but I found in this document:
Went out to move my car out of the way this morning and decided to test the AC again, compressor wouldn't even engage at all, button pressed in, set to different fan speeds, nothing.
What I have in my hand is the little box to the left of B-06 and closer to the fender of B-13. I can't find it in the Haynes manual anywhere. I believe B-06 is to the relay for the blower fan, even though it's called the Air Con Relay. Or a little bit of both, probably.
You should be able to use the black wire to send power to a switch to increase idle.. How to increase idle? I don't know. I'm trying to figure that out myself. I have a weber so perhaps a slight vacuum leak? Probably not.. my condenser has a small leak so need to fix that before I can really play around with it.
As for the drier? I found that rockauto has driers for RX-3s in stock and they use the same flare fitting. Part number: Four Seasons 33318. (Please note: I have purchased the drier but have not used it yet so I don't know for 100% it'll work but the flare sizes are the same)
Went out to move my car out of the way this morning and decided to test the AC again, compressor wouldn't even engage at all, button pressed in, set to different fan speeds, nothing.
What I have in my hand is the little box to the left of B-06 and closer to the fender of B-13. I can't find it in the Haynes manual anywhere. I believe B-06 is to the relay for the blower fan, even though it's called the Air Con Relay. Or a little bit of both, probably.
That sounds like the low pressure switch is keeping it from running...a leak would describe the poor AC performance on the highway. Sight glass on the receiver/drier? Should see liquid passing with maybe occasional bubbles.
The drier I got this time doesn't have a sight glass. Lame.
The AC not kicking on was because I left one of the plugs on the relay halfway out when I was testing stuff last night. Derp.
Once I plugged that back in, the compressor kicked on and then started making a clattering noise after running for a bit, and I immediately turned it off.
09-02-20, 05:32 PM
r152a Conversion on 79 Rx7
