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ECC climate control temp sensor measurements made easier

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This topic is in the MVS Volvo Repair Database » ECC Climate Control Temp Sensor Measurements Made Easier
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jreed
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Volvo Repair Database ECC climate control temp sensor measurements made easier

Post by jreed »

I'm in the process of trying to figure out why the ECC climate control system on my '97 855 GLT (158k miles) is unhappy and blinking its AC and REC lights at start up. As best I can tell the system functions as intended: AC is cool, fan blows normally, temperature tracking seems ok, position knobs for upper and lower vents direct the air properly, the recirculation switch makes the damper move into recirculate mode, etc. I'm just going through the system checking out components to try and find one or more that isn't working right.
Part of the process was to check that the two duct temperature sensors and two interior cabin sensors are working. Maybe somebody else already discovered this method, but I hadn't come across a write-up anywhere, so it was new to me: I found a way to do the resistance test on all four sensors relatively easily (no removal of sensors or disassembly of lower part of dash is required for this test -- though like me you may already have removed the panels and glovebox, etc, to check everything else out). All you have to do is to pull out the ECC control module from the dash, disconnect the three green connectors on the back. (Removing the radio first makes it easy to push on the back of the ECC module to release it from the panel).
Remove the three green connectors on the back of the ECC module.
Remove the three green connectors on the back of the ECC module.
ECC_Connectors.jpg (91.61 KiB) Viewed 12461 times
With the connectors disconnected from the module, take the large connector in the middle and locate the brown, yellow and green wires on the back.
Brown, Yellow and Green wires going into back of large connector.
Brown, Yellow and Green wires going into back of large connector.
I took a short length of thin gauge copper wire and inserted it into the connector to make the connection to these wires.
Measuring the resistance of one of the Cabin interior temperature sensors (the Brown-Green pair)
Measuring the resistance of one of the Cabin interior temperature sensors (the Brown-Green pair)
Above I'm measuring the Green "#2" connection (my #1 and #2 labeling numbers are arbitrary -- I don't know if green is driver's or passenger's side) and getting about 7.7kOhms resistance, which is close to the 8-12kOhms range described in the helpful "850 -95 AC Heater System Manual" pdf file. I figure I was reading 7.7kOhms because it was pretty hot outside when I was doing this test (~85-90F) and the pdf mentions that the resistance declines with increasing temperature.

Below I'm measuring the opposite side of the car (the Brown-Yellow pair) and getting 7.56kOhms.
Measuring the resistance of the Brown-Yellow (GND - #1) sensor
Measuring the resistance of the Brown-Yellow (GND - #1) sensor
Next I'm measuring the duct temperature sensors. The wires for these sensors are on the small green ECC connector that only has four wires going to it.
Duct temp sensor test
Duct temp sensor test
Here I'm measuring the Brown-Yellow pair and getting 8.3kOhms. I measured the Brown-Green pair and got a similar value.

Just thought I'd write this up as a quick and handy test to allow measuring all four of the interior temperature sensors in a relatively quick and painless way. All four of my temp sensors appear to be reading roughly similar values. I also checked that the fans located behind the cabin temp sensors appear to be spinning normally.

The fifth sensor in the AC system is at the bottom front of the car mounted to a metal tab right in front of the radiator (on my '97 -- I think '95 and earlier have a different type of sensor that is located near the windshield on the passenger side). When I tested that sensor I got about 500 Ohms, which matched the reading of the second temperature sensor located just above it in front of the radiator.
1997 855 GLT (Light Pressure Turbo) still going strong. Previous: 1986 240 GL rusted out in '06, 1985 Saab 900T rusted out in '95, 1975 Saab 99 rusted out in '95, 1973 Saab 99 rusted out in '94

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jreed
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Post by jreed »

Note there is actually a sixth temperature sensor in the system, located between the power transistor and the blower motor. It's accessible after removing the lower kick panel on the passenger side of the car. I'm going to go test that one next.
1997 855 GLT (Light Pressure Turbo) still going strong. Previous: 1986 240 GL rusted out in '06, 1985 Saab 900T rusted out in '95, 1975 Saab 99 rusted out in '95, 1973 Saab 99 rusted out in '94

JimBee
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Post by JimBee »

Another helpful writeup.
A couple of questions on sources that might help others:
Where did you get the measurement spec's and wire code index?
Also, I think there are two under dash sensors in that network on either side of the control module.

JB

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jreed
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Post by jreed »

Thanks for the feedback! I really enjoy reading what others have done here and it inspires me to document what I do trying to fix my car so I can share it back.

I got the measurement specifications for the temp sensors from the Volvo 850 PDF zip file that I downloaded from MVS.
( https://www.matthewsvolvosite.com/forums ... php?t=8018 )
The specific file containing the information is titled "ac heater system auto.pdf", a forty page gold mine of detailed troubleshooting data that blows away anything in VADIS.

I've attached a screenshot of the resistance specification info. A couple pages farther down in that document it spells out the colors of the wires involved.
Resistance specification for temperature sensors
Resistance specification for temperature sensors
AC Heater System Auto PDF screenshot.jpg (81.08 KiB) Viewed 12448 times
I went out this evening and located the sixth sensor, which measures the temperature of the air in the intake duct:
Location of intake duct air temperature sensor
Location of intake duct air temperature sensor
And probed it with my trusty cheap-o Harbor Freight Cen-tech multimeter (set to the 20kOhm scale):
Probes in place on pins
Probes in place on pins
And got a reading of 8.1kOhms:
Resistance measurement of sensor
Resistance measurement of sensor
This value is within the normal 8-12kOhms range, so I'm concluding that this sensor is OK.
1997 855 GLT (Light Pressure Turbo) still going strong. Previous: 1986 240 GL rusted out in '06, 1985 Saab 900T rusted out in '95, 1975 Saab 99 rusted out in '95, 1973 Saab 99 rusted out in '94

byeboy
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Post by byeboy »

Did I miss the part where you fixed the blinking lights?

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jreed
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Post by jreed »

No, I'm sorry to say you didn't miss it --- I haven't figured out why the lights are still blinking. Usually I like having a '97 model year, except when it comes to the ability to easily read out the diagnostic codes on the ECC.
1997 855 GLT (Light Pressure Turbo) still going strong. Previous: 1986 240 GL rusted out in '06, 1985 Saab 900T rusted out in '95, 1975 Saab 99 rusted out in '95, 1973 Saab 99 rusted out in '94

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Post by JimBee »

You mentioned that the air directional dampers are working, but are you sure they are all working? That one on the right side of the climate control unit, left of the glove box, is notorious for splitting out the damper shaft which is made of plastic. That might be one thing to check and repair if needed even if it's not the cause of the lights. If it's broken that means cold feet if you drive around in winter weather. You have to sleeve it to get it workable.

JordanW
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Post by JordanW »

Just curious if you knew you could read the codes for the ECC using the OBDII port, a 12V LED, and a switch? Granted, it's a bit of a pain, but it works. The directions are found at the top of the page here http://volvospeed.com/vs_forum/topic/47 ... formation/ right where it begins "To retrieve the flash codes the following procedure can be adopted..." If you buy a 12V LED it will have the resistor already.
96 850R = ARD Green m4.4, rip, Kilen's, C70vert subframe, S60R exhaust manifold, NA TB with 960 plate, SNAAB J pipe, MSD coil.

Matty Moo
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Post by Matty Moo »

That's only up to 1995. He has a 97.
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jreed
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Post by jreed »

JimBee-- Thanks for asking about the dampers and the damper shaft. To check those out, I turned on the ECC system and set the direction knob to defrost. I felt air blowing out towards the windshield from the vents on top of the dashboard. Then I turned the direction knob to straight forward and felt air only coming from the upper front vents. Then I turned the knob to floor and felt air coming from the floor vents under the dashboard.
Each time I turned the knob I looked in a the black plastic damper shaft and I could see it turning smoothly. I couldn't see any splits or anything that looked broken. So that part of the system seems like it is working normally.
1997 855 GLT (Light Pressure Turbo) still going strong. Previous: 1986 240 GL rusted out in '06, 1985 Saab 900T rusted out in '95, 1975 Saab 99 rusted out in '95, 1973 Saab 99 rusted out in '94

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