Air Conditioning Questions
 

It's summer and I'm in Texas so yeah, AC is a requirement. Also, my car is a 1995 R2 so I'm running R134a from the factory; not R12 like the earlier FDs. Since getting the car in January I haven't had a chance to really try the AC because I don't really drive the car yet. After getting the suspension all worked out I've been driving it sparingly and I notice a constant "hissing" from the glovebox area when the AC is on. Let me clarify and state that I mean the blower with the AC button pressed. No noise when the AC button is NOT pressed. Fastforward to today and Firestone is having some sort of $10 AC diagnosis promotion so I took it in.

After about an hour and a half wait they tell me it's very low on freon (which I suspected) and they are unable to really charge the system or determine if there are any leaks because the compressor won't kick on due to a bad relay. $300ish to fix it all. I politely said thanks but I really just came in for a recharge so I appreciate the diagnosis....and out the door I went.

So the moment I start the car I look at my idle RPMs; roughly 700rpm with JUST the blower fan running. I hit the AC button and the RPMs jump to just a tick over 1000rpm. I turn the AC off and the RPMs settle back down to where they were before. AC on, 1000rpm again. I did this 5 or 6 times just to be absolutely sure. I should also note that I get the hissing noise only when the AC button is depressed.

So my question is....this indicates the compressor is indeed kicking on and he engine is responding to the additional load of running the compressor...right? Is there ANY way this is NOT the case?

I think it only indicates that the EL unit is responding to the a/c button being in the on position.

Just look at the compressor itself, and you can see if the compressor clutch is engaged (when the a/c button is in). The a/c pulley should then rotate.

I would find a good independent AC shop to have a look at it - Firestone won't be much help there.

Typically any noises behind the glove box would be the expansion valve. I second what Books is saying, pop the hood and see if the pulley on the AC compressor engages.

It's quite possible that it's low, that's the #1 problem with AC on the FD is the refrigerant has leaked out.

From what I've heard the R134a systems don't cool as well as the old R12 systems, but that's second hand info. An FD with a good R12 system that's running right can put out 34 degree air at the vents.

The PowerFC (I think you have a PFC) will bump up the idle for the AC. I think it will only do it if it can actually turn on the AC - the ECU knows if the AC is running.

You can set the AC idle on the PFC, it may just be set a little too high.

Dale

Here's a video of what I've observed.....soooooooo I've been lied to, yes?

Yep, your compressor is turning on and off with the AC switch.

I don't know if I'd say you're being lied to, but Firestone isn't exactly the masters of all AC diagnostics. Hell, they're barely competent at putting tires on a car.

If your AC isn't getting as cold as you would like it could just be low. There's a wide range where you have enough refrigerant to engage the compressor but not enough to efficiently cool. Again, find a good independent auto AC shop, I bet there are plenty in your area. They can put a set of gauges on and see how the charge looks.

Also make sure your fans are coming on when you kick on the AC. No airflow over the condenser will make the AC system run hot.

Since you're heading a noise in the glove box there's also a possibility your expansion valve is having problems. The expansion valve takes the high pressure refrigerant and sprays it into the low pressure side - that is what makes the "cold". Same deal as turning a compressed air can upside-down and you see the frost coming out, good ol' thermodynamics. If it's stuck open you won't have good cooling. Again, the AC shop can tell this from their gauge readings.

Dale

All good advice. And in the video I do get a shot of the fans to prove those are turning on too.

I'll find an independent place and see if they can give me a straight answer.

If you feel comfortable, you're could buy a can of 134 and a gauge, some cans come with it and just add some freon.

you just set the gauge for the ambient temperature and add the freon until the gauge reads in the full range.

i bought a few cans a couple of years ago and they were about $5 at Walmart.

there is dye that you can add to check for leaks if needed.

As Dale indicated, because the compressor comes on, that indicates your system has at least the minimum amount of freon and is not necessarily full.

Well I went to a local place. Super small shop, 1 really old dude who ONLY does AC service. Anyway, I went and told him what was up and we charged the system and included some UV dye just in case. It blows a lot colder now and doesn't make as much noise.

Additionally, we were looking at the running engine while the system was charging and he said, "You know what, I'll bet the other guy was looking at your air pump." (mine isn't functional). And we both started laughing. I don't know what's worse, the guy from FireStone lying to me about my compressor not working or him being honest and not knowing which one was the compressor. :lol:

Anyway, end of job, thanks everyone for the help!

For what it's worth, my '95 with factory R134a works just fine, but did benefit from a charge. I did the cheapo home DIY can thing as I was pretty sure it had no leaks or underlying issues. It's been fine for the past two years. I've got about 60k on the vehicle now.

Remember too that automotive HVAC has gotten a lot better in 25-30 years. My FD will blow very cold when you are on the highway but in severe 90+ degree F weather and stop and go, it's not up to the level of a modern car. Also, with the low torque nature of the rotary and no electronic throttle you can feel the drag of the A/C on the engine much more than a modern car.

On my car when it was closer to stock the R12 system worked GREAT - ice cold air and nearly ZERO drag on the engine at low speed/RPM. I seriously couldn't tell the AC was on.

Then I had to put a front mount in and the AC has been so-so since then :).

AC that works right in an FD really works well - ice cold, very little drag, cools the cabin down fast. Problem is almost all the cars have had the refrigerant leak out by now or it's really low. The O-rings on the hot side of the engine bake from turbo heat, the small lines get holes rubbed in them, condenser gets holes from road debris....

Dale

Hoping my decision to go with a large smic will help matters in that regard. I have a fan that will pull air through the IC exclusively so it should keep it from heat soaking when sitting idle.

So glad to have the AC back to working 100%. The scrotum cooler under the steering column might be my favorite feature on this car. :D

Geez.... that's hilarious. It's likely they were looking at your air pump. The problem with those chain shops is that they hire anyone. If they said they've done an oil change on their lawn mower or own a screwdriver, that makes them qualified to be a tech there. It's a hardcore hit or miss situation with those places. It's best to use them ONLY for alignments and watch them as they do it. I'm glad you go it all sorted out. I have thermometer in my fd vent and on the highway on speed 2, I get 40 degrees. Speed 3 and 4 is almost unusable because of how cold it blows. It's actually uncomfortable lol

Scrotum cooler vent FTMFW.

I would caution people charging without a high side / low side manifold gauge set and some research on pressures/system function. You can easily overcharge just monitoring the cold/suction side of the system.

Safest way to charge is always by weight, which you can only do with a good machine or creative use of a precision scale

I got my R12 system repaired in 2017. Had to replace the evaporator, expansion valve and dryer. It took some work to find a good shop that I could trust that would be able to do an R12 fill, but I think it was worth it rather than switching to R134a. The system blows VERY cold.

Just wanted to follow up here and say the AC is working AWESOME! It's kinda overkill on anything past 2. The 3rd and fourth setting would be a blizzard. It's basically 100 degrees here so I'm LOVING it!

Awesome! What all didi they do to fix it?

Dale

Just a proper evacuation and recharge to spec.

Nice! Did they use 134a or R12?

Need to tear into my AC, I drove it 6 hours from Mississippi back home with the AC pretty much not doing anything at all. Was SO stupid hot.

Dale

I wonder if there is a difference between r12 system and 134 system besides the connector fitting and refrigerant. Does anyone know?

The expansion valve is likely different as that's the biggest change when converting an AC system properly. I don't know if any other parts are different but id imagine not.

So you recommended changing to a 95 expansion value if I have a 93?

The following applies to most auto AC systems:

R12 systems use a mineral oil. R134 systems use PAG oil. The two are not compatible. Mineral oil doesn't dissolve into R134 and isn't carried thru the system efficiently.

It is generally recommended that you replace the oil in the system with PAG if converting to R134. Evacuate...Remove, drain, and refill compressor, new drier. Translation - PITA.

R134 heat exchangers are usually sized larger than R12.

Because R134 molecules are smaller, the hoses generally have a barrier layer in them to stop long term leakage.

Never heard of anyone changing an expansion valve for a R134 conversion or any reason other than it stopped working. Not saying it doesn't help, but It's certainly not a priority compared to the oil as the wrong oil can kill a compressor.

Don't convert to R134 if you can avoid it. It doesn't cool as well. It will leak out of a R12 system fairly quickly for a number of reasons. It is still bad for the environment.

Find a shop that will charge R12 or top off your system with ES-12 hydrocarbon refrigerant: https://www.rx7club.com/3rd-generati...e-12-a-664882/

The ES-12 option is especially simple and effective if you just have a low pressure R12 system that needs a charge VS one that has been open to atmosphere for a while. ES-12 is compatible with mineral oil already in our R12 systems and has larger molecules that don't leak out as quickly.

I converted my Denso system to R134a with PAG oil and it's plenty cold. I don't get 38F vent temperatures but they're comparable to modern R134A cars.

I'm interested in seeing what an R12 equivalent would be compared to my current setup.

Glad to hear it works well for you. Maybe I shouldn't be so negative about 134. My Denso 134 conversion blew pretty cold, but leaked out in short order. I also had blower switch issues and crappy adapter fittings, so that was part of the problem. I never was able to find adapters that I believed would seal permanently.

I just ordered some more ES12 to top off my system because I never fully charged it to the 40 psi low side 200 psi high side recommendation. It is at 30/145 right now and still blows cold. I'll let you know how that goes once I get some more in there.

Mine doesn't leak much now (comparable to modern cars?), I put all new o-rings in it when I converted and it's held pretty well. My old o-rings leaked pretty bad.

My conversion fittings don't leak but the valves do seem to go bad pretty easily inside of them if you go to recharge after a few years.

30/145 is pretty low, I bet it would improve quite a bit with proper pressures. Keep in mind that 40/200 is still low for summer and that the ambient temperatures affect the recommended pressures a lot.

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