Year: 04/05
Make: Mazda3
Model: Sedan/hatch
Engine Size: 2.0/2.3
Refrigerant Type: R134A
Ambient Temp: 90
Pressure Low: 46
Pressure High: 32
Country of Origin: Japan

** Bump** anyone home? Care to respond?

http://www.autoacforum.com/messageview.cfm?catid=2&threadid=14994

All these values were taken after a few minutes, and every cycle (about 40 cycles for each setting) was consistent.

On Full Blast:
Cycle on: 8 C (46 F), about 10 seconds
Cycle off: 0 C (32 F), about 9 seconds

On Fan Setting 2:
Cycle on: 8 C (46 F), about 7 seconds
Cycle off: 0 C (32 F), about 17 seconds

At first I thought no one responded to your original post, but it appears they did -- in great detail.

In any event, at 90F -- unless there is absolutely no humidity and the interior is ice old -- the compressor should not be cycling, especially at that rate.

How about some pressure readings? None posted.

Has the charge been recovered and weighed to determine proper charge? Factory does screw up.

If this is an OT system, has a Delta T measurement been made? On a properly charged OT system the evaporator inlet and outlet temperature should be the same, or the outlet slightly colder than the inlet. If not I would add R-134a in 2 oz increments until this is attained. The compressor should stop cycling.

Any junk in the evaporator case?

Joe

This post was in reference to many Mazda 3 owners claiming they would like better performance from their a/c system. Dealer states system's are fine do to vent temp meeting OEM specifications. The quick cycling is not an issue to them if the vent temp meets spec.

Yes making sure you have a properly charged system is a must. This is even going to be more important with these new smaller capacity systems. This system has a capacity of 16.5 to 18.0 ounces. Not much margin to play with there and reduced refrigerant means smaller components!

One thing you might look into is a defective temperature sensor. There is a resistance range procedure for testing the sensor. Bad sensor could cause a quick cycle to occur.

-------------------------

When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com Contact: Arizona Mobile Air

The only difference between a manual and climate control system is in the ductwork and computer system which allows a preset temperature to be obtained by opening and closing various doors which allow heat to mix with the cold air which maintains a preset temperature.

It has nothing to do with the cycling of the compressor.

-------------------------
LAYem STRAIGHT

Compressors only cycle after the interior of the vehicle has been cooled, (humidity removed) , after that the evaporator core has reached the freezing point, (will ice over, blocking airflow) , therefore the need for cycling begins.

If the auto climate system were set to 85 degrees, then the compressor would not cycle due to the heat removal. Less cycling, longer compressor life.

-------------------------
LAYem STRAIGHT

I think there is a lot of confusion on how the AC system works...on all cars..I suggest getting a copy of the Mastercool AC repair manual which will explain in greater detail how a system operates. There is no gas in your vents. Only air that passes thru the evaporator core. There could be a dozen or so things that are wrong with the car(s) you are talking about, and "dealers" don't always find the answers. One of you may have to either wait until the car is out of warranty and bring it to a "real" ac shop, or risk losing your warranty to have it lookded by a proffesional AC tech. Lets face it, MAZDA says the system is operating properly. Obviously they are either wring, or unable to look past the factory maunal for the car given by the company. ATC operates differently than manual AC, but will still cycle when the evap reaches freezing temps. If you drive using outsode air, cycling should be less, and ATC uses outside air, blended with inside air for quick cooldown and is a different system in that regard. Hope this helps.

-------------------------
Chick
Email: Chick

---------------------------------------------

Freedoms just another word for nothing left to lose

What is the evaporator core temperature when the compressor cycles off? Before you going playing with cycle points you better know that answer or you are just going to create more issues! If the core is already at the point of freezing what is lowering the core temp 5 more degrees going to do? In the auto a/c world frozen is frozen and air will not travel through a frozen core! Now if the system is cycling at a core temp of 40 degrees dropping the cycle point by 5 degrees may help. Might see if you can find out what the dimensions of the evaporator core! Would be a starting point to determine if the core seems small or not compared to other vehicles in the same class.

-------------------------

When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com Contact: Arizona Mobile Air

"Unfortunately, my head is spinning here. If we use the outside air as opposed to the recirc with our manual A/C then we're getting warm outside air inside the car. Are you saying that the compressor will stay on longer if we use outside air as opposed to inside air and consequently, we will "feel" the cold air from the vents; therefore, the interior will be cooler than using the recirc feature"
------------------------------------------------------------------------------------------------------------------------------
If using outside air, the evaporator will take longer (sometimes) to drop to temp that cycles it off. Using cooled air will cause more cycling and drop the evap temp faster. (Heat and mositure already removed) I'm not saying you should do this, but it should cut the cycling times down a bit on a hot day...

-------------------------
Chick
Email: Chick

---------------------------------------------

Freedoms just another word for nothing left to lose

So I'm the guy on the mazda3 forums trying to look into this. Basically, from the service manual info, this system is totally controlled by a thermistor feedback to the PCM that cycles the compressor. no low pressure switching to determine whenthe low side has dropped below a switchpoint.

From the data we have from the manual, the cut-in temp is 41, the cut-out is 39F, using the thermistor,which is mounted at the evap, about center height, and slightly left of center.

In 90F ambient, I measured cycling at 10sec on, 6-7sec off (I suppose the strikexx?). I am using a solid temp digital thermo, stuck into the center vent all the way, with a 3" tip, and I have calibrated the readings. The steady-state reading is 43F at fan setting 2, recir air, all interior vents open. The thermo is integrating the temp readings, because it is not a thermocouple or instant-read, although it is pretty quick.
Model is EXTECH 39240.

Almost all of the complaints on the forums deal with fast cycling of the compressor, and it rarely stays on longer than 10-15 sec.

The service highlights manual from Mazda shows a little bit of the circuitry, and a graph of the thermistor resistance vs. temp.

What I did was to attempt to move the switchpoint of the vent air down by 5F or so by moving up the switchpoint of the thermistor by 5F.

To do this, I looked at the resistance at 40F (center of switching range, 6Kohm), the resistance at 45F (5K ohm) and calculated roughly what it would take to parallel the thermistor with to make 6K look like 5K, and came up with something below 33K ohm, giving it some margin.

After placing the resistor in parallel with the thermistor, the vent air dropped to 37.5F, and the cycle went to something like 25sec on, 6 sec off. It is still cycling, so I don't think it is freezing up, (I tried to leave some margin in the system) and as I stated in the mazda3 forums, if freezeup of the evap is an issue, we can up the added resistor to 47K or 56K.

I didn't really see any harm in trying this, because (help me out here) if the evap freezes, then it just wont blow as cold air, and the airflow will decrease, right?

My latest addition is a switch to switch in / out the parallel R based on how cool the interior is. Kind of like an ECON setting.

So Experts, without pressure gauges, because I really don't think there is an issue with the system given how it reacts after the change, and given the fact that many perople have verified the pre-mod operating points, do you think there is any reason not to do this, or whether there is a better solution?

WHAT is the huge resistance to dropping the gauges on this car all about? The service fittings can't be any harder to get at than some of the other stuff out there. If you really want to make the A/C work better, get some system pressures. Maybe they only sell this car to EE's?


Bill:
Moving the discharge temperature down will make the evaporator colder, and will cover up some of the problem - but can create others. Freezing the evaporator solid may cause a slow oil return to the compressor. The 39/41 setpoints are a fair setting to avoid evaporaotr icing in all climates. Regional adjustments used to be commonplace years ago, but now you get to deal with the world market car.

The system is equipped with a HIGH pressure switch. One of the reasons we keep asking for pressures, is to determine WHAT is shutting the compressor down. On a hot day with a small system, there should be no cycling - the evaporator temp should not drop below 40f unless there is an airflow issue. With good airflow over the evaporator, there will be a LOT of heat transfered to the refrigerant. This translates to high discharge pressures, and may be the actual reason for the compressor shutdown. A HPCO event may be viewed by the PCM as a different situation - the restrike delay may be longer to protect the system components.

Adding a thermistor bypass for local conditions is not all bad, but you should know all of the system parameters before doing so. I spent a LOT of time working around a PCM generated A/C problem, and had a ton of data before I changed anything. If you do need to lower the evaporator temp below freezing for cooldown, I suggest a time limited bypass. I have done this on systems for cooldown, allowing the evaporator pressure to drop to 12 psi for the first five minutes of operation - then returning to the original setpoint.

A set of gauges is a cheap investment.

.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Hey, I've got no resistance to taking the pressures, I just don't have the gauges yet. Sounds like the next investment. Thanks for you feedback.
Yes, the system does have a high and low pressure cut-out sensor. I can monitor that and see whether it ever kicks in.

Is the a FAQ you can point me to on purging the gauge lines beforeconnecting them to the system for taking the pressures? thanks.
And if any of you folks are around Austin, TX maybe some help?

Usually we check them at 1500 rpm.

-------------------------


Send me e-mail