AC compressor/ electric fans not working

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Frankv3499

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Hi all,

I was lucky to find your group! I have an 05 Yukon Denail 6.0 and when I fired it up yesterday, after several months of hibernation, I had a loud squeal and I assumed it was the AC compressor or a tensioner when I heard it.
I drove it into my garage and let it run for a while and when doing so, I tried to engage the ac and all it would do is flash the little snowflake on the hvac control and then the snowflake would go away without the ac turning on.
I have over 250k on the Yuk and I understand things wear out.
The bigger problem is that as I ran it, I realized that neither electric fan was turning on. I used my el-cheapo, Bluetooth obd reader on it to verify the engine temp and I could see it creep all the way past 220 degrees with neither fan turning on.

I guess that tells me that my coolant temp sensor is working? But, why would my ac compressor failing have anything to do with the fans no longer working?
I really couldn't care less about the ac no longer working. We only use this Yuk when the weather gets bad so I don't plan to dump that kind of money into it to replace the ac compressor (if it's bad).

I absolutely need those fans to work automatically when the engine temps rise, since it's shown me that it will overheat without them so, I am hoping that one doesn't require the other.

Can someone please tell me how to fix this or what to check for? The electric fan/fans could always be heard running when the ac would kick on. My coolant was full and I had pretty even temps across all of the under hood hoses when I checked with my thermometer.
The temp gauge on the dash works as it always did and it was quite odd to see it move so far past where it normally sits. My heat output was constant at the front and rear heat vents.

Thanks!
 
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Frankv3499

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I have been picking at this thing for 2 days. As of now, all that I know is that when I unplug the coolant temp sensor connector at the drivers side head, both fans run at full speed.

Does that indicate a bad coolant temp sensor??
My obd reader is telling me that my engine temp is now -38° with that sensor unplugged.
My garage is 75 degrees and the ac compressor clutch isn't locking up but the snowflake on my dual climate no longer flashes. It's remaining lit up.

Any advice?
Both cooling fans remain running on high with the ac/snowflake turned off
 

S33k3r

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How much is the sensor? If it is sufficiently inexpensive enough, and no one here has any other ideas, might be worth firing the parts cannon once.
 
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Frankv3499

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How much is the sensor? If it is sufficiently inexpensive enough, and no one here has any other ideas, might be

Yep. I almost assumed this may be a common issue and felt silly asking for help.
I ordered a Delco temp sensor. I found that it's hard to start hot and cold with the temp sensor unplugged.
It seems like the ac compressor may have taken a dump and that seems to correlate to the fans not running.
 

OR VietVet

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Welcome to the forum.

Like what @S33k3r said, go ahead and throw a sensor at it and double check that the wires are in good shape after the hibernation. Make sure a rodent has not chewed at the wires. Secondly, if refrigerant has leaked out of a/c system, the compressor will not turn on. You can unplug the low pressure sensor at the accumulator, cross the connections with a jumper and see what happens. The compressor should turn on if the problem was just low pressure. Make sure those wires in the system are in good shape as well.
 
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Frankv3499

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Welcome to the forum.







Like what @S33k3r said, go ahead and throw a sensor at it and double check that the wires are in good shape after the hibernation. Make sure a rodent has not chewed at the wires. Secondly, if refrigerant has leaked out of a/c system, the compressor will not turn on. You can unplug the low pressure sensor at the accumulator, cross the connections with a jumper and see what happens. The compressor should turn on if the problem was just low pressure. Make sure those wires in the system are in good shape as well.

Will do. Thanks for those tips!
 

ivin74

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I have been picking at this thing for 2 days. As of now, all that I know is that when I unplug the coolant temp sensor connector at the drivers side head, both fans run at full speed.

Does that indicate a bad coolant temp sensor??
My obd reader is telling me that my engine temp is now -38° with that sensor unplugged.
My garage is 75 degrees and the ac compressor clutch isn't locking up but the snowflake on my dual climate no longer flashes. It's remaining lit up.

Any advice?
Both cooling fans remain running on high with the ac/snowflake turned off
The fans are programed to on when the temp sensor goes out. If you disconnect them the ecm thinks the sensor went out and kicks the fans at full speed.
 

nonickatall

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Two things may come together here. A defective air conditioning system and a defective fan, because the two systems are intrinsically independent of each other.

Although the air conditioning switches on the fan, this is also controlled by the engine electronics to maintain the temperature of the engine.

I'm not very familiar with both systems on the GMT 800, but I know this system from many other vehicles and they are actually always structured the same way.

The fan has a fan relay which switches the fan on from the engine control, or from the climate control. I would check the fan fuse and relay first.

You can bridge the relay with a wire and the fan should turn on. I don't know where the relay is located but you will find out.

With air conditioning systems it is usually the pressure switch, as already written by @QR VietVet. Background: The air conditioner is charged with a predetermined amount of refrigerant, which is a gas and liquefies at a certain pressure. That's what the compressor is for. If there is not enough refrigerant in the system, the compressor will be extremely stressed and destroyed.

This is why the air conditioner does not switch on, when the pressure switch reports that there is not enough refrigerant in the system. Of course, it is also possible that there is another defect, e.g. that the magnetic clutch no longer switches, or the air conditioning compressor is even defective.

I would also first identify the pressure switch, bridge it and see if the air conditioning compressor starts. However, you should not let it run for long, just check whether the magnetic clutch switches on the air conditioning compressor.

If that doesn't work, I would apply 12 volts to the magnetic clutch on the air conditioning compressor to see if it switches.

If not, as well the compressor hat fuse and relay.

If all of these are the case, you have a harder-to-find defect, probably the air-condition control itself.
 

nonickatall

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I have been picking at this thing for 2 days. As of now, all that I know is that when I unplug the coolant temp sensor connector at the drivers side head, both fans run at full speed.

Does that indicate a bad coolant temp sensor??
My obd reader is telling me that my engine temp is now -38° with that sensor unplugged.
My garage is 75 degrees and the ac compressor clutch isn't locking up but the snowflake on my dual climate no longer flashes. It's remaining lit up.

Any advice?
Both cooling fans remain running on high with the ac/snowflake turned off
I completely overlooked this message, otherwise I would not have written so off topic.

As I said, I don't know exactly how it is with the gmt800, but most cars have two temperature sensors, one for the display instrument and a temperature sensor for the engine electronics, which of course also controls the fans.

If your fans runs when you unplug the sensor, the fans and relay are working. So it is very likely that the temperature sensor is defective.

It is slso possible that the air conditioning does not come on, because the air conditioning is switched off at low temperatures, because the cold threatens to cause defects and the cooling effect only works if there is a difference between the refrigerant temperature and the condenser temperature.

If I were you, I would replace the temp sensor and that should probably fix your problem.
 
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