Do you notice your AC temp fluctuating?

andrew61987 · May 19, 2016

On a hot day with my AC on full blast I notice some fluctuation in air temp. It goes back and forth between "kinda cold" and "super ice cold" on about 20 second intervals. Anybody notice this?

NAAC3TACO · May 19, 2016

When my 2008 was doing that I needed a recharge. I was about .5 lb low.

Lester Lugnut · May 19, 2016

When I saw the thread title I thought that maybe your compressor was short-cycling - turning on and off too soon due to an overcharge - too much refrigerant.

Then I read the thread and see "super ice cold". Short-cycling compressors don't usually make super ice cold air.

I also see your in Sacramento - assuming CA. Internet shows current temp to be 84F. That's not blazing hot.

A/C may very well be doing it's job. Again - it's not that hot outside so it's not necessarily going to take that long to cool things down and cycle the compressor.

Just my 2 cents.

andrew61987 · May 19, 2016

Lester Lugnut said: ↑

When I saw the thread title I thought that maybe your compressor was short-cycling - turning on and off too soon due to an overcharge - too much refrigerant.

Then I read the thread and see "super ice cold". Short-cycling compressors don't usually make super ice cold air.

I also see your in Sacramento - assuming CA. Internet shows current temp to be 84F. That's not blazing hot.

A/C may very well be doing it's job. Again - it's not that hot outside so it's not necessarily going to take that long to cool things down and cycle the compressor.

Just my 2 cents.
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It was 97 yesterday and I was noticing it. Still cooled the interior of the truck adequately, I'm just hoping it's not a sign of trouble to come.

Lester Lugnut · May 19, 2016

andrew61987[OP] said: ↑

It was 97 yesterday and I was noticing it. Still cooled the interior of the truck adequately, I'm just hoping it's not a sign of trouble to come.
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If it's cooling nicely in 97 degree weather, I would say all is well.

RCRcer · May 19, 2016

Not exactly the same problem but.... I was in Sacto yesterday, it was hot. My truck had been sitting for a couple of weeks and no previous A/C issues. I took the truck for a drive up towards Tahoe. Turned the A/C on and warm/hot air. WTF, shit, I'm thinking a dealership warranty issue is my future.
Fiddled with it a bit and still blowing hot, left it on and low and behold it started blowing cold air. Turned it off until blowing hot and then back on, turned cold again.
Anybody else experienced something like this, or any experts on what may have caused this?

iK0NiK · May 19, 2016

I've owned two 2015 Tacomas and both have done what's described in the OP. Both brand new trucks off of the lot.

AC will get very cold, then fluctuate between ice cold and just cool.

I did a lot of research on that and basically found a consensus that the AC in the Tacoma is functioning as designed. Here are the super informative replies I found:

iroh said: ↑

U need a little deeper understanding of AC regulation. The compressor can't just run forever; the evaporator will get very cold, which feels awesome until ICE grows all over it and blocks the airflow. If the evaporator is blocked when the compressor is running, there's a chance some unboiled refrigerant will make it to the compressor and hydrolock (aka DESTRUCTIFY) the thing. The system will periodically lower the refrigerant pressure to allow the evaporator to warm up.

There are multiple monitoring methods, but the most common are either a thermistor or temperature-calibrated switch very near to the evaporator core's output side.

For the former, the thermistor will lose resistance as it gets colder, and as a calibrated sensor the computer can tell when it's at the proper temperatures to turn the compressor off (cold enough) and back on (warm enough). I did a little trick on my Fit with its thermistor - I made a 190k ohm parallel switched circuit that would trick the computer and give me the choice of either a 45-55F range (stock) or 34-42F range (killer on summer days... passengers always said "PUSH THE BUTTON!")

With the latter, there isn't much of a computer needed. A temperature-regulated switch performs the same function as the computer-thermistor system, but there isn't much adjustability capability with that one. However it is very simple and inexpensive.

You may be referring to the multiple types of compressors there are. The Tacoma's (as well as most vehicles) use a clutched non-variable compressor. It simply shuts on and off. Some more expensive compressors are capable of lowering output pressure on the fly to facilitate the warming process, which gets rid of that annoying on-off surging ours do.

When it starts cycling that much, either the system is calibrated for a high temperature (my Fit was like that, it cycled 4-5 times a minute on low fan. It's a lot faster to cool to 45F than it is to 35F), or the refrigerant is low. It can trip the low pressure sensor once it moves enough refrigerant into the pressurized side, causing a repeating rapid cycling.

The blower fan in the truck also regulates cycling as it controls airflow across the evaporator. It will cycle a lot on speed 1, but will likely never turn off on speed 4. You can use this to rule out whether low refrigerant is your issue.
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BARTRD said: ↑

Normal. Every time it cycles off the air temp will rise. Then the comoressor cycles back on and the air temp drops. The extent of how much the temp rises and falls depends on things such as outside temp and humidity. But it must cycle off to keep the system from freezing, just like Iroh stated in his post above
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j4x4ar3 said: ↑

Here's something for you techies and those that like "hidden" features on the Tacoma. This one happened to me three times under the same conditions however on the third time it happened (today) I had a Scangauge and was watching things and found what I consider to be an undocumented feature of the A/C system that helps prevent overheating.

Today it was 107 degrees where I live so the A/C was in full force use. Normally the coolant temperature of the truck runs about 190 degrees consistently when the outside air temp is 90 or less. Today the coolant temp ran about 195. Unfortunately though I live in California in one of the worst commute areas and today of all days some yahoo decided to crash and block traffic for a couple miles on the freeway. That coupled with the fact that I ascend a 1000ft pass which is about 5% grade made things even more interesting since I was crawling at <5mph. Soo.. watching the coolant temperature out of curiosity I slowly watched it climb to 200+ but an interesting thing happened at 213degrees. At 213 I heard my A/C recirculate damper close and sure enough I looked down and the recirculate light was on. Pressing it would not allow me to turn it off but pushing the A/C button shut the whole system down. I turned it back on though because it was hotter than heck outside. It was still getting cold as well. At 220degrees though I noted that the A/C compressor cycled off and when it did the recirculate light turned off as well. Warm air started coming out of the vents as well but not for long. When the A/C compressor turned back on the recirculate light turned on again as well. This did this about 5 times before traffic strarted moving faster. Although I was still climbing the pass but now about 40mph the temp dropped back under 220 and the A/C no longer cycled. Once the coolant temperature dropped below 213 the recirculate light turned back off as well and everything started getting cold as normal and the button functioned fine as well.

Previously when I didn't have the Scangauge I automatically paniced and thought the A/C unit was malfunctioning and simply shut it off and opened the windows. Since I had the scangauge I was watching the coolant temp and the needle to see how far it would go before the needle rose up. It never really did move so I just left the A/C on to see what would happen.

Sorry for the long post but I thought some might find this interesting should you happened to be in really hot weather and find your A/C doing funny things. I personally think it's a great function so if you forget to turn off your A/C when climbing grades on hot days then the system will take care of itself. Don't have to worry about those signs that say "turn off air conditioner"
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You can also read up on these threads:

https://www.tacomaworld.com/threads/a-c-system-cycling.227619/

and

https://www.tacomaworld.com/threads/hidden-a-c-feature-to-prevent-engine-overheat.11254/#post-125388

Jimmyh · May 19, 2016

Excellent and informative post! And right on the money.

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Do you notice your AC temp fluctuating?

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