How cold is your AC?

[pasadena_commut]

Now that the flashing 2/3 problem is licked I'm once again reminded that the AC itself isn't very cold on my car. This doesn't surprise me since the 323 I had before it also didn't cool very well. I just had an Aha moment when planning tonight's dinner, when I realized that our instant read electronic meat thermometer works at a low enough temperature to actually measure this, so we can compare apples to apples instead of the subjective "pretty cold" sort of thing. I'm going to measure mine in the shade, posting numbers for both the ambient temperature and the outlet temperature for fan position 4 on fresh and recirculate.

If any of you already have these values, please post them.

 

[gus5]

I live in Texas and we've already had 18 days over 100 degrees. If my car has been in the sun, it usually takes about 30 minutes of driving for it to really cool the car down. If the car has been in the shade (like my garage or a parking garage), the AC blows cold pretty much instantly and it cools the car down pretty quickly. Even when it's 105, I'll have to turn the fan down to 2 because it's to cold. My car has tinted windows which seems to help alot when it's sunny outside.

I've read a lot of complaints on here about the AC being weak in these cars, but my experience with it is it works about as well as any other car i've been in/owned.

 

[CheeseHelmet]

Mine works ok, especially on the highway. At idle it'll keep the car cool but only if it was cool to start with (eg. drive on the highway a bit then hit traffic).

Regarding the coldness test, the service manual actually has a test you can do on page 07-10-2 (REFRIGERANT SYSTEM PERFORMANCE TEST).

Here's the procedure:

1. Place a dry-bulb thermometer in the driver-side center ventilator outlet.
2. Close the hood.
3. Warm up the engine and run it at a constant 1,500 rpm.
4. Set the fan switch to 4th position.
5. Turn the A/C switch on.
6. Set the RECIRCULATE mode.
7. Set the temperature control to MAX COLD.
8. Set the VENT mode.
9. Close all the doors and all the windows.
10. Wait until the air conditioner output temperature stabilizes. The output temperature is stable when the A/C compressor is repeatedly turned on and off based on the A/C compressor control of A/C amplifier.
11. Determine and record ambient temperature.
12. Verify that the temperature reading is in the shaded zone.

 

[pasadena_commut]

Regarding the coldness test, the service manual actually has a test you can do on page 07-10-2 (REFRIGERANT SYSTEM PERFORMANCE TEST).

Thanks for finding that page.

I bet that even for a P5 in perfect condition that graph only holds when the test is performed in the shade. The real test of an AC's performance is how it does on a hot day in a car in direct sunlight, and historically, that's where Mazda's AC comes up short. For us the gold standard was the AC in our late lamented Subaru Legacy, which had so much oomph that it could make the cabin not only cool, but cold, on a 105 degree day in full sunlight. Even the AC in our Honda Civic Hybrid is better than the P5 in actual use. (And the HCH does it with only a tiny 1.3 liter motor.)

 

[pasadena_commut]

I realized that our instant read electronic meat thermometer works at a low enough temperature to actually measure this, so we can compare apples to apples instead of the subjective "pretty cold" sort of thing. I'm going to measure mine in the shade, posting numbers for both the ambient temperature and the outlet temperature for fan position 4 on fresh and recirculate

That didn't work out too well.

The ambient temperature was 82 F, and while this wasn't in the shade, it was 5:30 PM and the Sun was pretty low. On the P5 the temperature at the outlet dropped to 45 F and then rebounded back to 48 F. For comparison did the same measurement on the HCH, which was parked right next to the P5. There the outlet temperature dropped only to 49 F before rebounding to 51 F. Which is odd, because the inside of the HCH was definitely cooler than the inside of the P5. (The HCH is white, the P5 dark blue.) Both tests lasted about 8 minutes, but I didn't time either one. One complication - the air kept pushing the thermometer out of the vent so I had to hold it there. (The thermometer has a large flat display, which makes it easy to read, but acts a bit like a sail.)

Before declaring the outlet temps too high I guess I will also need to:

1. Verify the calibration of the meat thermometer at these low temperatures.

2. Do a much longer test, since the AC may not have been at the equilibrium state described in the manual.

 

[CheeseHelmet]

Did you close all the vents except for the middle ones? And most importantly, did you run the engine at 1.5K RPM?

 

[pasadena_commut]

Did you close all the vents except for the middle ones? And most importantly, did you run the engine at 1.5K RPM?

No and Sort of.

Why would closing the other vents decrease the temperature at that one vent? More flow sure, but there was already plenty, so I don't think air from the cabin was flowing back into the vent, and the probe was all the way into the vent.

The RPM didn't want to hold steady at 1.5K. On the P5 I aimed for that, but it was wandering around a bit. On the HCH I just let it idle.

 

[d0sitmatr]

I dont use my AC much, Im one of those weirdo's who is happy as long as the air is flowing
but on those rare occasions my wife asks me to turn it on, or I notice my son is sweating, it seems to be decent enough, not exceptionally cold at first, but after a short time gets pretty darn cold.

my 99 ranger however, that air was frigid right from the start, if I started running it on #2 fan, within a couple mins I would have to drop it down to #1, and sometimes even turn the dial about 1/8-1/4 warm.

 

[CheeseHelmet]

No and Sort of.

Why would closing the other vents decrease the temperature at that one vent? More flow sure, but there was already plenty, so I don't think air from the cabin was flowing back into the vent, and the probe was all the way into the vent.

It makes a noticeable difference, you can feel it with your hand.

 

[pasadena_commut]

It makes a noticeable difference, you can feel it with your hand.

Hmm. I guess it won't hurt to try. Off the top of my head I'm thinking what you perceive as cooler air may be wind chill. Closing the other vents will increase the speed of the flow through the one remaining open one, and that will pull more heat off your hand even if the actual air temperature doesn't change. Plus it would increase evaporative cooling on the skin of that hand. So the air might feel colder without actually being colder. (The same way air feels cooler in front of a floor fan, when the air temperature is actually exactly the same as in the still air in the same room.)

 

[CheeseHelmet]

Hmm. I guess it won't hurt to try. Off the top of my head I'm thinking what you perceive as cooler air may be wind chill. Closing the other vents will increase the speed of the flow through the one remaining open one, and that will pull more heat off your hand even if the actual air temperature doesn't change. Plus it would increase evaporative cooling on the skin of that hand. So the air might feel colder without actually being colder. (The same way air feels cooler in front of a floor fan, when the air temperature is actually exactly the same as in the still air in the same room.)

That makes perfect sense, sorry I wasn't thinking straight this morning.

 

[Tiajaunatoad]

A couple of quick observations on vent outlet temps vs fan speed. The slower the fan speed the colder the air is coming out of the vent. This is because at a slower speed the evaporator has more time to cool the air coming across it. At higher fan speeds the temp at the vents is not as cold but you have a lot more volume so it helps to cool the whole interior quicker. The last couple of days where I am temps have been in the high 90's and my 02 p5 takes about 15 min to get it cool enough to stop sweating in stop and go city traffic. Once I get out on the highway I have to have to make adjustments pretty quick to keep from being to cold. I've checked outlet temps with a Fluke meter and temp probe and on 4 the outlet temp is 47 to 49 deg. When I turn the fan down to 1 the temp drops to 40 to 43 deg. Those temps air with a/c set on recirculate by the way.

 

[north42g]

Walmart sells a $20.00 multi-meter with a built in thermometer- pretty acurate actually. I relied on it when my FLUKE meter died and I sent it in for warranty service.
Any way- The factory recomends that a a A/C service be performed every season for optimal cooling.
Using a Recharge machine/vacuum machine removes any air and moisture by creating a vacuum inside system which in turn boils of moisture and revitalizes the A/C system.

HVAC ASE Technician

 

[pasadena_commut]

I looked up the specs for the thermometer I used, which was an Acurite 00645W3. Walmart sells these (albeit listed under a different name on their web site, but you can see the actual name in the picture)

http://www.walmart.com/ip/Mainstays-Digital-Meat-Thermometer-00641W/14913168

for around $10 (don't recall exactly). It is supposedly accurate from 0C to 200C. Cold water from the fridge read 38F, so I think the thermometer probably gave an accurate reading.

Any way- The factory recomends that a a A/C service be performed every season for optimal cooling.

Seriously? Who has their A/C serviced yearly? That said, perhaps it is time for mine since it seems to be blowing air 7 or 8 degrees F hotter than the manual specifies.

Hmm. Do these cars have a cabin filter? I don't recall seeing one, but if there is one it must be filthy, since it hasn't been changed/cleaned in 5 years.

 

[Hank3]

Do these cars have a cabin filter? I don't recall seeing one, but if there is one it must be filthy, since it hasn't been changed/cleaned in 5 years.

No cabin filters for the US models. I thought I read somewhere that the Canadian ones did, however.

 

[CheeseHelmet]

No cabin filters for the US models. I thought I read somewhere that the Canadian ones did, however.

Nope, only the European and Japanese ones had them as an option, see: http://www.mazdas247.com/forum/showthread.php?123631445-Protege-cabin-air-filter-Installation

 

[pasadena_commut]

Took the AC in for service. The guy said it was contaminated and hooked it up to a machine to clean it out and change the freon. However, he didn't think it was running much colder after than before, because the compressor was shutting off when the outlet temperature got down to 42F. Maybe the "freeze up sensor", or whatever it is called is set too high? In any case, the outlet never got near 42F in my initial testing, and it was much hotter yesterday than when I made my measurements, so maybe it is working a little better. Subjectively, the cooling doesn't feel very different. In particular, it still takes a while to start blowing cold.Will have to wait for another 80F day to measure again.


It was a great test of my A/C flicker fix though. When I picked up the car it had been sitting in the sun at around 99F for an hour, and it was painfully hot inside. But the AC light was solid in all 4 fan positions.

 

[CheeseHelmet]

Protip: http://lifehacker.com/5823069/how-to-quickly-cool-down-your-cars-oven+like-interior

 

[pasadena_commut]

Protip: http://lifehacker.com/5823069/how-to-quickly-cool-down-your-cars-oven+like-interior

LOL. I just open all the windows and the sunroof. Even after doing that bare metal, like a seat belt tab, is still hot enough to cause a burn.

 

[Megazuel]

Took the AC in for service. The guy said it was contaminated and hooked it up to a machine to clean it out and change the freon. However, he didn't think it was running much colder after than before, because the compressor was shutting off when the outlet temperature got down to 42F. Maybe the "freeze up sensor", or whatever it is called is set too high? In any case, the outlet never got near 42F in my initial testing, and it was much hotter yesterday than when I made my measurements, so maybe it is working a little better. Subjectively, the cooling doesn't feel very different. In particular, it still takes a while to start blowing cold.Will have to wait for another 80F day to measure again..

What kind of "contamination" was found? Was there R-12 or another freon blend present? Were there hydrocarbons? Did he see debris in the oil recovered? Just curious, because I have sold and performed many A/C services, including a few on P5's as of late. Freon doesn't get "contaminated" on its own. If the system was tainted with R-12 or another blend then that could cause issues with the performance of the compressor.

More than likely your issue is simply freon level. Its not unusual for a perfectly normally functioning system to loose a portion of its charge over time. My 03 P5 is pushing 9 years old, and while I have yet to service my own system, I wouldn't be surprised if I evacuated it and didn't pull the full factory charge back out. Were you told how much freon was recovered from the system? What were the high and low side pressures before and after the service?

As it so happens, I had my digital thermometer in the dash on Thursday afternoon when the ambient was about 100. After about 3 minutes, center ducts were at 60 degrees on fresh air and after another 5 minutes on recirc. it was down to about 46, with the windows up. The general rule that you want at least a 30 degree drop over ambient is still used today, just heard it again from a MACs trainer at a class a few months back. Most systems today are capable of more, however the charge levels keep getting smaller, so loosing a few ounces can mean the difference between having a 98% charge and having a 65% charge. That can make a big difference in how cold it gets, how fast it gets cold and how long it can stay cold.