A/C Inside AND Outside Temps Both Wrong
Thread Starter
Race Director
Joined: Jun 2001
Posts: 10,084
Likes: 3,056
From: CA
A/C Inside AND Outside Temps Both Wrong
My inside and outside temps are both about 10-12 degrees too low. I can't believe both sensors failed the same day and by the same amount. Anyone else have this problem, and how did you fix it?
Example: Outside temp 70 degrees. Reads 59.
Inside temp set to 70. Inside temp actually 81.
Thanks,
Michael
Example: Outside temp 70 degrees. Reads 59.
Inside temp set to 70. Inside temp actually 81.
Thanks,
Michael
Thread Starter
Race Director
Joined: Jun 2001
Posts: 10,084
Likes: 3,056
From: CA
I just checked the voltage at the outside temp sensor (near the bottom corner of the radiator on the passenger side), and it read 5.06 volts. I think it should read 5.0 volts, and a high voltage would tell the computer that the temperature is low (simulate higher resistance).
I was wondering if a couple people could unclip their outside temp sensor, and tell me what voltage they get on the connector.
Thanks,
Michael
I was wondering if a couple people could unclip their outside temp sensor, and tell me what voltage they get on the connector.
Thanks,
Michael
Drifting
Joined: May 2000
Posts: 1,917
Likes: 3
From: Southern NH
The better test is to check the impedance of the sensor with an ohm meter. The voltage seems normal assuming you measured an open circuit at the connector.
The HVAC control unit uses a 5V reference voltage and 5.06 is fine. At 68*F, the sensor should measure ~12.5k ohms and the voltage drop across it would be a ratio of the sensor impendance and the reference impedance somewhere between 0.1V and 4.9V.
If the sensor fails as an open circuit, the HVAC will default to about 56*F, close to what you're seeing on the display. Since the sensor is known to fail, I would guess that's your problem but also check the connector for corrosion since that can also lead to incorrect temp readings.
Now when you refer to the internal temp, I assume you're measuring it with a hand thermometer of some type. But since the outside air temp sensor is off, it could affect the internal airflow temp resulting in a higher than expected temp before the inside temp sensor can start adjusting.
The simplest thing to do is verify the outside sensor is bad with the ohm meter and replace it before doing anything else. It's relatively cheap and easy.
The HVAC control unit uses a 5V reference voltage and 5.06 is fine. At 68*F, the sensor should measure ~12.5k ohms and the voltage drop across it would be a ratio of the sensor impendance and the reference impedance somewhere between 0.1V and 4.9V.
If the sensor fails as an open circuit, the HVAC will default to about 56*F, close to what you're seeing on the display. Since the sensor is known to fail, I would guess that's your problem but also check the connector for corrosion since that can also lead to incorrect temp readings.
Now when you refer to the internal temp, I assume you're measuring it with a hand thermometer of some type. But since the outside air temp sensor is off, it could affect the internal airflow temp resulting in a higher than expected temp before the inside temp sensor can start adjusting.
The simplest thing to do is verify the outside sensor is bad with the ohm meter and replace it before doing anything else. It's relatively cheap and easy.
Thread Starter
Race Director
Joined: Jun 2001
Posts: 10,084
Likes: 3,056
From: CA
Originally Posted by JC in XTC5
The better test is to check the impedance of the sensor with an ohm meter. The voltage seems normal assuming you measured an open circuit at the connector.
The HVAC control unit uses a 5V reference voltage and 5.06 is fine. At 68*F, the sensor should measure ~12.5k ohms and the voltage drop across it would be a ratio of the sensor impendance and the reference impedance somewhere between 0.1V and 4.9V.
If the sensor fails as an open circuit, the HVAC will default to about 56*F, close to what you're seeing on the display. Since the sensor is known to fail, I would guess that's your problem but also check the connector for corrosion since that can also lead to incorrect temp readings.
Now when you refer to the internal temp, I assume you're measuring it with a hand thermometer of some type. But since the outside air temp sensor is off, it could affect the internal airflow temp resulting in a higher than expected temp before the inside temp sensor can start adjusting.
The simplest thing to do is verify the outside sensor is bad with the ohm meter and replace it before doing anything else. It's relatively cheap and easy.
The HVAC control unit uses a 5V reference voltage and 5.06 is fine. At 68*F, the sensor should measure ~12.5k ohms and the voltage drop across it would be a ratio of the sensor impendance and the reference impedance somewhere between 0.1V and 4.9V.
If the sensor fails as an open circuit, the HVAC will default to about 56*F, close to what you're seeing on the display. Since the sensor is known to fail, I would guess that's your problem but also check the connector for corrosion since that can also lead to incorrect temp readings.
Now when you refer to the internal temp, I assume you're measuring it with a hand thermometer of some type. But since the outside air temp sensor is off, it could affect the internal airflow temp resulting in a higher than expected temp before the inside temp sensor can start adjusting.
The simplest thing to do is verify the outside sensor is bad with the ohm meter and replace it before doing anything else. It's relatively cheap and easy.
BTW, I recently bought an Extech Multimeter which in addition to the typical volts and amps, it also has a thermocouple and infra-red inputs temperature inputs. The thermocouple is the way to go to check the system - very easy and fast.
I'm keeping my fingers crossed that the system stays running OK.
Thanks!
