1997 960 Flashing AC Blue light, No Heat, ECC Code 214

Delucadana · Post by **Delucadana** » 20 Oct 2013, 18:45

It's October in MA and time for heat but our 1997 960 has no heat. This just occurred, it was working fine a week ago.

Symptoms:
The vent blows only luke warm air regardless of setting. (The A/C hasn't worked in years but that's not the problem.) With the fan on auto the fan speed automatically increases when temperature knob is turned up to max heat or max cool but does not change speed when knob is turned up/down from 64° to 80° and fan slows down when turned away from the max or min settings. It's as if the internal temp sensor thinks its warm already.

The blue A/C light is still flashing once per second but it initially stays off for about 20 seconds then starts blinking. This happens with key in on position even w/o engine running.

Have tried the following with no success:
1. Replaced thermostat
2. Flushed out heater core in both directions with garden hose and found no blockage
3. Checked that the vacuum-controlled flow valve on the heater core port freely operates and is not frozen closed. Zip tied it in open position in case vacuum was failing (not sure if vacuum opens or closes it) but core intake and return are both the same hot temperature so hot coolant is flowing freely through the heater core. At this point I suspected the passenger compartment temperature sensor but then I found the ECC diagnostic procedure, which can detect problems with the in-vehicle temperature sensor and it didn't.
4. Ran the ECC self-diagnostic procedure and retrieved code 214 via the flashing blue lights, which indicates: Servomotor fails to operate within 10 seconds.
Does that mean the servo motor is bad or could there be a simpler issue like linkage? I found instruction for replacing the vacuum servo but is that the same thing as the servomotor? What does it take to replace servomotor and could I handle it in under four hours? If it takes more than that, I will let a pro do it. I could not find any instructions for replacing a servomotor.
Thanks,
--Dana

danr960 · Post by **danr960** » 21 Oct 2013, 10:23

One thing I might do would be to check for any vacuum leaks. I am not sure on the '97 if the servo motors are electric, or vacuum controled. Maybe there is a sensor that is telling the computer the servo is not moving. If it is moved by vacuum pressure, then maybe there is a leak in the vacuum system.

Check the hose at the fire wall near the a/c dryer. Follow that hose to the intake manifold and check the rubber elbows. The elbows have a tendency to rot out on the under side, so be sure to inspect their undersides. Also check all other vacuum rubber hoses, the leak may be small because a larger leak would cause an idle problem and trigger a check engine light.

Or you could have a failed servo motor, which there is one that is a common problem and real head ache to repair. There are short cuts that will not require dash board removal, but even these are not for the faint of heart. Most just plug the offending vacuum hose and live with limited control settings.

DanR '94 964 387,000 miles (153,000 on the new engine)

lindy8_man · Post by **lindy8_man** » 25 Oct 2013, 18:19

Ok, it sounds like the cabin temp sensor has failed. It is in your dome light. Front side you can see a little hole (about 1.5 MM) with a thin sharp probe inside. That's your baby! Be careful when removing the dome light as there is a big plastic clip that is prone to break... if it hasn't already.

I would also get under the car and look for your temp sensors outside. They are plugged into your brush guard. There are 2. Both need to work properly for the ECU to know what the outside temp is. Your ECU should be throwing a code if one of those has failed.

Also that "blue AC" light that is in the bottom left corner is not an AC light. IT is telling you it is freezing outside... What does the digital temp gauge say? That it is flashing tells me there is a problem there. When freezing conditions persist, it will be solid... which tells me you might have a short in one of those sensors under the hood.

Delucadana · Post by **Delucadana** » 28 Oct 2013, 13:51

Lindy, Thanks. I have eliminated the in-vehicle sensor as the problem. I checked the vacuum tube connected to the dome light sensor and felt a vacuum pull when the vehicle is running so that means interior air is being sucked over the sensor. Next I removed the whole dome light assembly and connected my voltmeter to the thermistor, heated it to 89º F then stuck it into a cooler with ice and measured resistance over a temperature range of 89 to 39 degrees Fahrenheit. The thermistor nicely varied linearly over the whole range from 4.7K ohms at the high temperature end to 21K ohms at the low temperature end. I even plotted the data points for fun. See attached excel chart.

Thermistor characteristics.xlsx: In-vehicle sensor performance; (31.45 KiB) Downloaded 204 times

I think I have logically eliminated the coolant temperature sensor because as I understand it, that only prevents the fan from blowing cold air before the engine is warm. Since the fan blows, I'm concluding that the coolant sensor is sensing heat.

That leaves the ambient sensors. I'll test those next right after I find them.

Dan, I think the servo motor is electric only because of the word "motor". Also I think the servo motor works because at one point, only for 20 seconds though, I got good hot air out of the vent. I believe the servo motor controls a baffle that allows air to flow or not under certain conditions i.e., based on the inputs from all the sensors and temperature controls. So for any hot air to have come out, it means that the servo motor moved the baffle at least once.

Delucadana · Post by **Delucadana** » 28 Oct 2013, 18:24

Found only one external ambient temperature sensor under the radiator hanging off a cable. The sensor was tucked inside the frame support just under the radiator on the driver's side. Disconnected and bench-tested it in the same way I tested the in-vehicle sensor. It's good. See graph of its temperature characteristics. Interestingly, it has different characteristics than the in-vehicle sensor. It has a negative temperature coefficient (NTC) meaning the resistance goes down as the temperature goes up like the other sensor but the resistance range varies from 350 ohms at 90º F to 1117 ohms at 43.5º F. See attached graph of the data points I measured.

Thermistor characteristics.xlsx: (31.44 KiB) Downloaded 238 times

The two connector pins to the sensor from the cable were all green so I cleaned them up and cut and cleaned the wires, soldered the connector pins to the cable for a reliable connection and reconnected the sensor.
Warmed up the engine and tested. Still no heat.
There are two codes from the ECC diagnostics, 214 (servo motor) and 161 (something to do with the light sensor on the dash). I shined a flashlight light on it and put it in direct sunlight. Neither would clear the 161 code. As I understand it, that light sensor on the dash only functions to lowers the temperature setting by 3ºC when in direct sunlight to compensate for solar heating of the passenger compartment. Not likely to be the problem.

BTW, the in-dash digital readout of the external temperature is correct. I suppose if I had checked this first I would have concluded that the external temperature sensors were good and saved the test. I'm assuming that the ECC computer must read the external sensors and drive the digital display on the dash, so that would mean the computer is at least reading the sensors correctly and correctly talking to the digital display. Maybe it only reads one of the external sensors and the other is broken?

So I will look harder for the other external ambient temperature sensor. Any other ideas? Thanks.

lindy8_man · Post by **lindy8_man** » 01 Nov 2013, 20:44

Well, my s90 had 2 sensors. My brush guard broke off and the sensors were dangling, and eventually failed... Then I failed smog test and had to replace them both. They were located near the bottom corners of the radiator. Since I don't have a brush guard any more, they are tucked up behind that aluminum sub frame.

The vacuum servos are also called a motor. assuming there is no blockage in the heater hose, and the coil is getting hot, and the fan is blowing... And your temp sensor is working properly. I think you have a door in the air handler that is not opening to allow the hot air in. could be the "motor" or the linkage has failed.

Delucadana · Post by **Delucadana** » 18 Nov 2013, 10:34

After exhausting other possibilities, we concluded (see above) it must be the servo motor or linkage which I did not want to replace by myself. So we asked a Volvo mechanic to change it and he did it successfully for about $550. That solved the problem. The 960 now has heat! So that credits the ECC diagnostics which pointed to the servo motor to begin with. We were hoping we could out-smart it.

Thanks for the help!