redrx82004

I read a lot of threads and there doesn't seem to be a sure fix for the AC cycling from warm to cold. I got my AC amplifier changed and they completely drained the AC and recharged it, but I still get warm to cold blowing from my AC. It's a little cooler now, but I would like to get it fixed once and for all. Everytime I bring my car to the dealer it's a 300 mile round trip and I have to take a day off work. It's been to the dealer three times for the AC problem.

Razz1

You just did get it fixed. It ain't gonna get any better.

Wrap the A/C tube it helps.

MDRX8

I think you gor it fixed also. Mine has been in the shop on and off going on 4 weeks. Sounds like you got the best it is going to get. good luck

Nubo

I think the only "fix" is going to be bypassing or "fooling" the controller. The compressor spends more time off than on.

RX8_Buckeye

In case anyone doesn't know, the reason the compressor cycles on and off in all cars is to prevent the condensation on the compressor from freezing up. If you are going to attempt something like this, be aware of the potential consequences.

Nubo

^^ yep - understood. But ain't nothin inside my car in danger of freezing at this point .

Either that, or the coils ARE freezing/thawing etc. But airflow is not reduced so I don't think that's it.

There are some specifications regarding the temp sensor which is near the evaporator coils. If I recall it is mentioned that the physical placement of that sensor is critical. So that's probably the first thing I'll be checking to make sure it's in spec. However I suspect that the system is detuned for fuel economy reasons.

macnrx8

There was a DIY thread on here about wrapping the ac line along the firewall with some high temp insulation but I couldn't find it. The person who started the thread said it did make the ac a little cooler.

NavyDood

This seems to be hit or miss with ppl. Our RX-8 works the same as it did the day we picked it up a year ago. Works great here in the summer TX heat.

bxb40

I agree ^ Hit or miss
The AC amplifier did it for me...

therm8

If you wrap the "cold line" as mentioned above and in the DIY section, the refrigerant doesn't warm nearly as much when flow decreases. I think this is the reason for the bursts of warm air we get every now and then. If you leave the AC off, drive around a bit, and then feel the line it gets extremely warm due to heat soak. This can only adversely affect the system when it is operating. It'll still cycle, but it'll go from cold to cold, instead of cold to warm. At least in my experience.

redrx82004

Thanks for the info guys

Razz1

It's in the DYI section. Believe me it works!

I just asked the engineers at work who are proffesionals in heat transfer and combustion.

After all we build industrial Turbines.

To put this to bed, wrapping the A/C line works. The A/C line is facing extreme temperture rising from an engine that is twice as hot as a piston engine.

BaronVonBigmeat

This has to be the correct answer. It's clearly a computer problem (and not a freon/compressor problem, the car CAN blow cold air for a few seconds), but I'm sceptical about the "precaution about freezing lines" theory. Other cars--Mazdas included no doubt--have much colder A/C's and don't have any problems. Of course those other cars aren't teetering on the edge of incurring a gas guzzler tax, thus we get cheezy fixes like 5W-20 instead of 5W-30, and a ECU that's stingy with compressor useage. Maybe someone will come up with a ECU piggyback that turns the compressor on more often.

Anecdotal evidence: When I first got my car, the A/C was fairly weak. Okay, maybe it's just not broken in or something I thought. That turned out to be true, and things improved. After a year of use it was actually blowing (somewhat) cold. Then I got my Huper Optik tint--wow, now it was really freezing! For a whopping three days. Then this cycling crap started. I can't imagine how uncomfortable I'd be without the tint.

The ideal thing would be for all 8 owners to keep bringing their cars in over and over to show Ford/Mazda that their "free" solution to MPG problems aren't free at all. In the meantime, I guess I'll try the A/C line reflective wrap. :sigh:

StealthTL

iTrader: (1)

1/We know the compressor CAN compress, but cycles off too soon.

2/We know the evaporator CAN get really cold, sometimes the air is under 40*.

3/From the "insulate the frosty pipe" thread, we can glean that the freon is exiting the evaporator in a very cold state....


What can we infer from this?
-I first thought the evaporator was protecting itself from freeze-up - they usually have a bulb in the fins that will override the settings when near freezing. However, this protection would only kick in after a good period of use, not during the first minutes after turn-on.

-Another quirk of the '8, that no one has mentioned so far, is the freaking HOWL from the air moving system at any setting over '2'....my money is on whatever restricts the airflow. You can't have good flow AND that kind of screaming 'velocity' noise, the two only go together in jet engines! If we can find the restriction(s), the air will move faster over the coil, the freon will pick up more heat, and the 'frosty pipe' will be back at room temp and efficient.

S

RX8_Buckeye

All I'm saying is that it is not a good idea to override the PCM to prevent the compressor from cycling on/off. I'm not claiming that the cycling is optimally tuned--fuel economy concerns may well be part of the tuning scheme. However, one question that popped into my mind just now is whether the EPA fuel economy test procedures call for accessory usage. I believe that the procedures are run without A/C on, in which case fuel economy would not drive the tuning of the compressor cycling. I'll have to look into this.

Also, do you really think 5W-20 oil is a "cheezy" fix for fuel economy? If I'm not mistaken, Mazda's 2.3L I-4 and 3.0L V-6 (along with the new 3.5L V-6) all use 5W-20 oil. It's becoming more and more common to use thinner oils to save on fuel economy, so I hardly view the RX-8's use of 5W-20 as "cheezy".

Razz1

"However, one question that popped into my mind just now is whether the EPA fuel economy test procedures call for accessory usage."

Do you have an answer yet?

gr8jab

When the AC is cycling on and off, what is the frequency and duty cycle? (In other words, how long is it on and how long is it off?)

It wouldn't be hard to delay the ecu 'off' signal to the AC by several seconds or longer. It just takes a cap, resistor, and diode. The time constant is the key (how much delay), and a potentiometer would probably make that easy to adjust.

The only problem is this would also impact the high RPM shutoff function.

EyeBall Fixer...(o)(x)

Here is the link to the DIY you requested earlier.

TeamRX8

iTrader: (25)

mine works great in the TX heat too, even with the frosty pipe uninsulated, go figure ...

Nubo

Well I'm tempted to try the wrap just for the heck of it. On the other hand I can't imagine the under-hood environment is all that ferocious. There are any number of plastic/rubber parts and they haven't melted or burned yet... Compare the heat-soak potential through this single wide pipe to the radiant surface area of the condenser coils that the refrigerant passes through to shed heat... Small potatoes. But, yeah, I'll probably do it

As far as extending the duty cycle or "fooling" the ECU I think the key may lie with the sensor that's near the evaporator coils. Just have to get the ECU thinking that it's warmer than it otherwise would think. That way you still get the RPM cutoff. Still speculation at this point, though.

Zoom49

the key may lie with the sensor that's near the evaporator coils. Just have to get the ECU thinking that it's warmer than it otherwise would think.

This is the key to our A/C issues, Need to fool this sensor with a resistor or move it to a warmer location in the evaporator coil to increase the compressor duty cycle. Compressor now shuts off before evaporator coil is completly cool

bxb40

I keep posting advice for people to try the pipe insulating mod ($10 and 30 min of your time). My case might be worse because due to the MS front strut bar, I do not have the engine cover in place, so that pipe sees all the engine bay heat.
I think it really works. Yesterday I drove with two other people in 92F and the AC was too strong at some point on recirculation (fan on 2), so I opened to air (even the person in the back said that it was strong enough).
Today there were 98F and the car stayed out in the sun all day. In 10 minutes it was all nice and cold. Under no circumstances my AC worked this well before the updated amplifier and the pipe insulation (anything above 90F was simmering time...).
So yes, I am a believer now - don't know why it works, but it does. Also, the AC works better at higher RPMs, so forget about gas milage... and stay cool

Chrisbert

Nice Stealth. I wonder if anyone who has had their dash off has looked for a kink in the works. Or, our fan may cavitate at high rpms.

beachdog

How about refrigerant additives like ice32? Anyone here try it? I don't have any issues with mine but enough people have problems that it might be worth a try.

www.ice32.com

Supposed to improve gas mileage too.

red_rx8_red_int

sounds too good to be true, imho