A/C turning off when idle

[jmandawg]

Hi all,

I've been having this issue lately. After driving for 30 minutes or so, if i stop at a drive through or in traffic for a few minutes, my a/c sometimes stops running and start to blow warm air. The A/C light is still on, but if i push the button and turn it off and then push it again to turn it back on the car stats idling rougher and the a/c comes on.

Seems intermittent as it just happens randomly. Today when it happened at the fast food drive though i opened the hood, and the radiator fan was running, but it didn't sound like the a/c compressor was running. I toggled the a/c button and it started.

One time it happened and it i didn't toggle the button, but once i started driving again it came back on.

Any ideas?

[CTScott]

The AC ECU is shutting it off. This could be due to low or high pressure on the sensor (i.e. low or overcharged refrigerant) or the pressure sensor being bad.

[jmandawg]

Thanks, what is the best place to start? Hook up some guages and look at the pressure? My brother has some, but i'm not sure how to read them.

[CTScott]

The easiest way to diagnose is using a Toyota Techstream tool, since it can talk to the ECU, but other than that the gauge route works as well.

Here are some pics from when I charged mine of what the gauges should look like:

Charged with the AC running:


Charged with the AC off:


And, this is the info that Techstream reports on the AC:

[Ben_]

Could be an issue with the condenser not turning enough vapor into liquid to feed the low side of the system. If the system only works when ram air is going through the condenser that is a good clue to start a diagnosis. Use a manifold gage pictured above to measure if the pressures are at the right levels when the system is running or figure out how to read the measurements the cars computer and sensors are reading. There is at least one sensor on the high side of the system on my car and probably one on the low side near the evaporator inside the cabin

[Ben_]

I am taking my a/c class at school right now and would love to help you try to diagnose it. You can buy a gage set at harbor freight

[jmandawg]

Sorry it took so long, had to go over to my brothers place to use his guages.

Here is an image of the reading while the AC was running. It was 77F outside at the time. I know there is only one fan for the radiator and the condensor, but does it have a hi and low speed? It sounded like it was running at high speed for like 10-20 seconds and then it seemed to be running at low speed the rest of the time. Maybe it's supposed to be running at high the entire time.

Also there seems to be some green dye in the system already as it sprayed everywhere when we disconnected the hose.

[CTScott]

That looks fine. So in that case, it could be that the pressure sensor (mounted by the sight glass under the hood) is not properly reporting to the AC ECU (that has been a relatively common problem). Toyota only sells the sensor as part of the entire tubing assembly for about $250. I have a spare one that I would be willing to part with for a whole lot less if that sensor is bad.

If you have a multimeter you can pull the connector from the sensor and take two measurements on the sensor's connector:

If you look at the connector you will see the wire colors. Measure the resistance between the pins where the respective color wires plug in:

10K between the grey and black wires
6.4K between the yellow and black wires

[Ben_]

The specs from Mitchell online service information system says the low pressure should be 21.7-36.2 and the high should be 198.7-227.7 when the system is stabilized. I can't read your gages but that's what the OE spec is. This is with the doors open at room temperature blower fan on high recirculate on ac on at 1500 rpm technically. I looked this up for class the other week so I could test my system and my car showed these numbers after a minute or so of running the system

Doing a resistance test on the sensor is a great second step I agree with ctsscott, of course. He is the guru of all things yaris

Also you can do a little bit of diagnosis by feeling the lines in the system. The inlet of the condenser should be hot to the touch due to it being next in line from the outlet of the compressor. The outlet of the condenser should still be hot(warm) but less hot than the inlet. The fan will cycle at whatever speed the ecu tells it to depending on a multitude of variables so I don't think that will tell us anything about the operation of the ac system

[CTScott]

His gauges are showing perfect readings (35 low and 210 high).

[Ben_]

Good stuff. The computer must be goofed if the system is physically ok

[Bluevitz-rs]

Make sure your condenser and rad are not blocked up with leaves or dirt. Poor airflow could cause the system to overheat and shut off.

[Ben_]

^good point. Blocking air flow through the condenser or damage to the fins (its the first thing to get hit by rocks going through the grill) would definitely cause problems. The good news is that if you have to replace the condenser the receiver/dryer is a part of that assembly so it will mean that you can replace both in one fell swoop. An ac shop will still have to do the repair so the refrigerant can be captured and then replaced. The refrigerant sold at Walmart and other stores would not be suitable since it has gunk it it to seal small holes that could and will most likely plug up your txv metering device and cause big issues

[jmandawg]

CTScott, I test the resistence:

12.09K between the grey and black wires
7.26K between the yellow and black wires

Does this mean it's bad? Also it looks like changing it requires a full discharge/evac/recharge?

[Ben_]

I'd be curious what the tolerance is, but that doesn't sound terrible. I'd be more worried about OL (no connection)

You can use the FSM posted on microimage and look at the section for the ac system. It will probably require discharge/recharge

Is your condenser is good shape visually?

[CTScott]

Originally Posted by jmandawg

CTScott, I test the resistence:

12.09K between the grey and black wires
7.26K between the yellow and black wires

Does this mean it's bad? Also it looks like changing it requires a full discharge/evac/recharge?

Those are fine. The next step is to check the sensor's actual output while the system is on.

To do that you need to measure the following. To do so you need to poke something tiny and sharp through the wire insulation and into the wire (I like to use a small sewing needle):

Voltage of the yellow wire to ground (should be 5 Volts)

Voltage of the grey wire to ground (should be between 0.76 volts and 4.74 volts)

[Ben_]

At school we use t pins from any office supply store. They are thin and relatively strong and have a good area to touch your meters test leads to
http://www.officedepot.com/a/product...d-T-Pins-Pack/

[CTScott]

Originally Posted by Ben_

At school we use t pins from any office supply store. They are thin and relatively strong and have a good area to touch your meters test leads to
http://www.officedepot.com/a/product...d-T-Pins-Pack/

The only problem with things like that with large heads is the potential for them touching something that they shouldn't and creating a whole new issue. That's why I stick with sewing needles.