Cooling fan and AC clutch

[MarkZ]

I have a 2000 STS and the radiator fans do not come on. It seems to be keeping the AC clutch from being able to click on as well because the the AC will turn off a few seconds after the car starts. The radiator fans should be running on low speed whenever the AC is on so I believe the AC looks for the fans and thens shuts off when they do not run. I can pull the relays and jump them and the fans run, I can make them run slow or fast, I can also jumper the AC relay and make it run just fine as well. I assume it is looking for a common sensor/relay that is shorted/faulty somewhere. Would a bad coolant temperature sensor cause this? The coolant temperature will go to the the 12 oclock position and doesn't move from there, which is odd since the cooling fans do not work. I have replaced (in the past) the radiator, water pump and hoses and even the engine was replaced right before it hit 100k miles due to a spun bearing(thank God for the extended warranty)

[Göran W]

Any codes?

[Cadillac Jim]

In the 1997 model year, the same fuse that powers the A/C compressor clutch powers the cooling fan relay coils.

In the 2002 model year, the fuses are separate for the A/C compressor and the cooling fans. Two of the cooling fan relays have their own fuse.

The problem sounds like an issue with one of the cooling fan relays or with a cooling fan, and the PCM is turning everything off. If so, there will be an OBD code that tells the tale.

[JimD]

I have a 2000 STS and the radiator fans do not come on. It seems to be keeping the AC clutch from being able to click on as well because the the AC will turn off a few seconds after the car starts. The radiator fans should be running on low speed whenever the AC is on so I believe the AC looks for the fans and thens shuts off when they do not run. I can pull the relays and jump them and the fans run, I can make them run slow or fast, I can also jumper the AC relay and make it run just fine as well. I assume it is looking for a common sensor/relay that is shorted/faulty somewhere.

The compressor clutch solenoid can be cycled ON/OFF by either the A/C Pressure Sensor or the A/C Low Side Temperature Sensor. When the PCM senses the compressor clutch relay is NOT energized, the PCM logic assumes A/C is not selected ON and the fans are then cycled as a function of coolant temperature.

I would look at the high side and low side pressure values at the compressor and be certain the system contains the specified amount of refrigerant.

Would a bad coolant temperature sensor cause this? The coolant temperature will go to the the 12 oclock position and doesn't move from there, which is odd since the cooling fans do not work.

Unless you are under the hood with a flashlight looking at the fan blades, you cannot tell if the fans are running or not. With the hood closed and engine idling, I cannot hear the fans running even when I know they are running.

Your fan control circuit uses three relays and the same setup has been used in many GM front wheel drive vehicles for decades. The weak link (if there is one) seems to be a relay failure.

[Logan]

That is a good point. The fans at low speed are pretty much unnoticed..

I attached a schematic of the 2000 STS cooling fans.

[Cadillac Jim]

Thanks, Logan. That is pretty much identical to what I have for the 2002 STS.

I'm thinking that, since the compressor comes on for a few seconds and then shuts off, either its low on Freon or there is a fan problem and the PCM is shutting off the A/C. Either way the OBD codes should tell what's up.

[MarkZ]

Ok, thank you all for ideas. I tested all applicable relays and fuses. The thing finally threw a code. P0480, it appears the PCM never sends the signal to the fan relays. I have the front shroud removed so I can monitor the fans. They do not come on at all, engine running for awhile, A/C on etc. I can jump the relays and they work great so I assume the PCM is not energizing the relays. Would that keep the A/C compressor from running and the fans from running? I assume my issue is before the PCM, is there a sensor that could be bad which would not let it ground the circuit to energize the relay? If I understand the diagram correctly it energizes by allowing the ground to complete. I would think an electrical diagram for the cooling system would help. The diagram for the fans is simple and was much appreciated, it allowed me to rule a number of things out.

[Cadillac Jim]

P0480 means that the circuit form the PCM to the fan relays isn't working. First, I would check the fuses in the two end relays. Then the obvious - the connectors to the relays and the fans.

The rest of the schematic probably won't help much. The only other one for the cooling system is for the engine coolant level indicator. Everything is operated by modules through relays. The fan circuit that Logan posted is essentially identical to what I have for the 2002 STS. Presuming that the A/C schematics are the same, too, here is the list:

Figure 1: Blower Motor - Front
Figure 2: Blower Motor - Auxiliary
Figure 3: A/C Compressor Clutch
Figure 4: Electric Actuators
Figure 5: Temperature Sensors - LH Drive
Figure 6: Temperature Sensors - RH Drive
Figure 7: Steering Column Controls

The A/C compressor schematic is unremarkable, except that it shows a thermal protection switch in the compressor. Its operated by a relay controlled by the PCM from power that is "Hot in ON and START." It shows the refrigerant low temperature sensor connected to the DIM, the refrigerant pressure sensor connected to the PCM, and the DIM, PCM, and IPM (A/C controls) connected through the car's CAN network.

And, yes, the PCM won't turn on the A/C compressor if the fans aren't working. It's in the software. The P0430 tells us that the problem is in the circuit that Logan posted.

[MarkZ]

Let's rule out the fan wiring schematic. I tracked the diagram back to 25 C1 at the PCM and ohmed and tested the wiring from the PCM to the relays and to the fans. If I trick it right at the PCM and create a ground on the proper dark green wire the fans run just fine. The question is what keeps the PCM from being able to create the ground to complete the fan circuit. Is there a sensor that is not completing the circuit before the PCM can ground the fan relay to turn them on? I checked the onboard (dash) codes and found a P0532 A/C refridgerant pressure sensor circuit low voltage code as well.

[JimD]

....Is there a sensor that is not completing the circuit before the PCM can ground the fan relay to turn them on?

Indeed there is; the Engine Coolant Temperature (ECT) sensor.

But before I type my example of a no-cost but time-consuming method of checking the operation of the ECT sensor, let me refer you back to post #4. You have not said word one about A/C system pressures or refrigerant level.

The whole fan operation question has been made out to be much more complicated/convoluted than it is or needs to be. Back to post #4; the cooling fans have two distinctly separate operating modes.

One mode when the A/C compressor is actually active; this cooling fan mode ensures there will be airflow through the condenser IF the vehicle happens to be in stop-go city traffic. We can't allow passengers to get uncomfortably warm just because the vehicle is not in motion.

The other mode is when A/C functions are not selected ON (therefore the A/C compressor is not active). In this mode the cooling fans are toggled ON/OFF and high speed/low speed strictly as a function of the ECT value.

And since your A/C compressor is not active, your cooling fans are under the control of the ECT sensor and only the ECT sensor.

[JimD]

....I checked the onboard (dash) codes and found a P0532 A/C refridgerant pressure sensor circuit low voltage code as well.

This important information was added while I was responding to the unedited post. Above is the reason why your A/C compressor is not active which is the reason why your fans appear to be misbehaving.

See post #4.

[MarkZ]

The fans are not coming on under either condition. I believe I have two issues here. I am going to pull a vacumn and recharge the A/C unit tomorrow to rule that out and go from there. The fans do not come on even after 10-15 minutes of driving in a hot NC summer, nor does the temperature gauge ever much go over half way even when sitting still with the fans not running. Electrical demons........

[JimD]

The fans are not coming on under either condition. I believe I have two issues here.

Possible but not likely.

I am going to pull a vacumn and recharge the A/C unit tomorrow to rule that out and go from there.

Locating the leak would also be good.

The fans do not come on even after 10-15 minutes of driving in a hot NC summer, nor does the temperature gauge ever much go over half way even when sitting still with the fans not running. Electrical demons........

If or when you ever want/need to dig into the whole issue of when the fans are commanded into which mode, I'll repeat the offer of a no-cost time-consuming method as mentioned in post #10.

[MarkZ]

I will gladly take you up on that! The A/C leak was addressed by fixing a high side line leak, new dryer, new orifice tube and pulling a vacumn which it held overnight then charged. I am concerned that there is too much oil in the system though so I am going to reclaim the system tomorrow to measure it before pulling a vacumn and recharging. I believe my gauges on my viper A/C reclaiming/vacumn,charging machine are lying to me though so I am borrowing a seperate set of gauges tomorrow to verify. I do want to note that the A/C issue was a past repair and the fan issue came a few weeks later. I will not rule out them being related though!

[KHE]

I will gladly take you up on that! The A/C leak was addressed by fixing a high side line leak, new dryer, new orifice tube and pulling a vacumn which it held overnight then charged. I am concerned that there is too much oil in the system though so I am going to reclaim the system tomorrow to measure it before pulling a vacumn and recharging. I believe my gauges on my viper A/C reclaiming/vacumn,charging machine are lying to me though so I am borrowing a seperate set of gauges tomorrow to verify. I do want to note that the A/C issue was a past repair and the fan issue came a few weeks later. I will not rule out them being related though!

Why are you thinking there is too much oil in the system? Was oil added at some point? The only way to remove the oil is to pull and drain the condenser, compressor, and accumulator - a lot of work.

With the proper refrigerant charge in the system, is it cooling properly?

[MarkZ]

How do I reset the service AC message on my dash? 2000 STS

[JimD]

Clear all the codes.

[MarkZ]

I did that with my OBD scan tool. How about on the dash?

[JimD]

Maybe your scan tool cannot handle "B" or "C" or "U" codes. Try this:

http://www.caddyinfo.com/readingcodes.html

[MarkZ]

That is what I was looking for. Thank you.