Ambient Temp Sensor Testing?

jcrews

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If you are talking about the IAT, you can use VCDS. Look at measuring group 007 in the engine after it has cooled off, preferably at night.
 

JB05

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A new CTS cured my erratic temperature gauge, even though the engine performed normally.
 

DanG144

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If you are talking about the one for the AC system, under the plenum, I have seen two types (I think). One type is truly a switch - it opens when below 35 F or so.

The other type is a thermistor, you can check the resistance with a multimeter. Mine read 1.1 kohm at 75 F or so.

 

tron2003

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I was talking about the outside temp sensor for AC purposes, it's located behind the cowel on the left side of the car..... follow up the crack between the drivers door and the left front fender. It will be located in behind the top of the fender just below the left bottom corner of the windshield.... remove the black plastic under the hood to access it.
 

DanG144

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I think it is supposed to read low resistance when above about 35 F.

Not sure about the sound; I have no experience with that type.

What has you looking at it? AC issues?
 

tron2003

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Yes, A/C issues plus I just had a wiper motor go out so I figured I would double check that as long as I was right there.
 

commanderjjones

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I don't mean to hi-jack your thread, but would either of those sensors cause my A/C to not work unless it is hot outside? I've had this issue for several days and it's becoming annoying.

The A/C won't work in the mornings (around 70 degrees) and I have difficulty getting the windshield to unfog on the way to work.

On the way home from work (90+ degrees), the A/C works fine.
 

DanG144

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It is a small cylinder, about half as long a tube of chapstick, located in the windshield plenum, under that plastic grill, on the car left side. Two wires run to it.
 

commanderjjones

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It is a small cylinder, about half as long a tube of chapstick, located in the windshield plenum, under that plastic grill, on the car left side. Two wires run to it.
Before I start tearing things apart, is it accessed from outside or under the dash? From what you are saying, I'm envisioning it is on the opposite side of where the cabin air filter is located?

Sorry for all of the newbie questions.:D
 

DanG144

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You are correct. Access from outside. Pull the wiper arms. Pull the cabin filter cover. Pull the black plastic trim grill (carefully, they get brittle).

It is easily found after that.

Rodents love to chew the wires off of them.
 

tron2003

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Before I start tearing things apart, is it accessed from outside or under the dash? From what you are saying, I'm envisioning it is on the opposite side of where the cabin air filter is located?

Sorry for all of the newbie questions.:D
What did you find out? What were you getting for an ohm reading?
 

tron2003

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I got 1.1 kilo ohm on my 2005 Jetta.
Hmmm, really makes me wonder as I was getting .7. I was in the 200 ohm setting. When I bumped it up to the 2K setting I obviously was getting 0.0.

Of course mine is an '00 Jetta opposed to your '05. Can anybody with an '00 style chime in?


 

commanderjjones

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What did you find out? What were you getting for an ohm reading?
I've been working my butt off the last several days and still haven't had time to tear into it. The problem is still there.....the A/C will work fine for a while, cut off the engine and it may or may not work the next time. It's driving me crazy and it's too damn hot to be driving around without A/C.:mad:
 

seaglf

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I have been having the code p0128 on my scan gauge, and actually have used my VAG COM. I realize that it could be from a faulty temp sensor or thermostat,but I have changed those. And used the improved green sensor. Anyway I still get that code intermittently. I also had issues with my AC, but replaced the fans and it worked fine for awhile. Now it doesn't work at all.

One of the VW dudes I took it to said something about the ambient temp sensor passably causing the code i'm getting. This was before I had AC problems.

Could that sensor trigger the code and the subsequent loss of fuel mileage and power loss, and if its completely out would the AC stop working.
 

jcrews

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The outside air temperature switch only bypasses the AC when the temperature is too cool. Most are switches. I have a thermistor, but the FCM uses the information the same way.

Your problem is with the cooling system or the signal from the ECT (either the ECT is faulty or there is a wire problem).

You'd have to log group 007 with VCDS to see what's happening. To set P0128, the warm-up time has to be very slow (>15 min above a minimum start temperature).
 

seaglf

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The outside air temperature switch only bypasses the AC when the temperature is too cool. Most are switches. I have a thermistor, but the FCM uses the information the same way.

Your problem is with the cooling system or the signal from the ECT (either the ECT is faulty or there is a wire problem).

You'd have to log group 007 with VCDS to see what's happening. To set P0128, the warm-up time has to be very slow (>15 min above a minimum start temperature).
thanks I will try that when I can.
 

rackaracka

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How can you tell if you have a switch or a thermistor? I am troubleshooting no voltage at the AC clutch on my 2002. (fans run when ac is switched on). I've pretty much gotten it down to the ambient temp sensor or the pressure sensor, or the fan control module - but would like to test before I just buy more parts.
 

DanG144

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I am not sure how you can tell by year model, etc. - at least not definitively. I think the 2000 and before may have the switch, and the later ones the thermistor. But you can measure the resistance, put it in the freezer and measure again, if you have the thermistor, you will see a signifigant resistance change.



It seems to me that the ambient temperature switch/sensor being open circuited prevented the fans from working, too, not just the clutch. Perhaps you could try plugging and unplugging your temperature sensor and see if your fans turn off and on?
You can also use a 1kohm resistor, I think to temporarily replace the thermistor for testing.
 

tooreal

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I've been having Air Conditioning problems with my 06 Jetta TDI, and I Hope someone here can Help me? My A/C had started acting up about 5 weeks ago, it was blowing warm air on a Hot Day.
I ordered a New RCV to replace the old one that Broke while I was taking it out of the Compressor to check it out and clean it up. I pulled a vacuum on the system and weighed in the factory recommended 17.75 Oz of 134A, then cleaned the Radiator and Condenser Coil with foaming coil cleaner to push out the bugs and Crud that had built up over the last 9 years of Driving. Everything went back together perfect and Looked Great too, but it didn't fix my problem! The air conditioning will Only put out 44°F with the fan set on the #2 speed. If I set it up to fan speed #3 the ait temp goes up to 52°F, and if I set it on #4 it goes up to 60°F , then if I set the Fan on Recalculate mode the temperature goes up even more. The pressures on my Gages read 36 on the Low side and 125 or 150 on the High side which I believe is right on the money.
I found the Thermistor for the Blower Motor N24 located under the dash on the passenger side Extremely Hot and probably causing the Discharge air temperature to be about 10° Higher than it should be, I would have to think? Could this cause the problem that I am having?
What would cause the Thermistor to put out So Much Heat? I Thought it was a secondary Heating Element when I pulled it out (and caught it for a Nano Second) before I quickly let it hit the floor.. The fan won't run without it, but is it supposed to get that Hot in the Summer when Running the Air Conditioning?
Anyone have any ideas?
Thanks in advance for any Help..
 

AndyBees

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The faster you push air through the evaporator the less it is cooled..... the contact time is reduced with fast moving air.

Seems your low side pressure is a bit high. It should be more close to 30 psi or slightly lower. The high side pressure should be s bit higher too. Of course, you never told us what the ambient temp was when you obtained those pressures. .... it does matter.

The resister pack (thermistor) is just that, a resistor. Thus, it does produce heat. If the fan is working on all speeds, the resister pack is just fine. There is only one speed that the resistor pack will virtually produce no heat, that's high (full 12 volts to the fan). Being located in the fan housing provides needed cooling for the resistor, otherwise, it's life expectancy would be tremendously reduced.

Unless I am badly mistaken, the recirculate option only shuts off out side air. That's why it's called "recirculate" never allowing a fart to leave the cabin.
 

meerschm

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The resistor pack for the air fan just has resistors in it. (and a fuse)

while the resistance will vary a slight bit with the temperature, (which goes up as the resistor turns current into heat), that is not a property used for anything.

they do get hot, which is one reason they can burn out.



A thermal resistor (thermistor) is made to have a resistance value that changes quite a bit as the temperature changes, which makes it useful to measure the temperature. Later cars measure the temperature of air used for combustion in a couple places, as well as several places in the HVAC system, and even more in the exhaust system. one of these is used to source the measurement of ambient temperature.

What a thermistor is made of changes for the application, as does the specific resistance curve over a useful temperature range.
 
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