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George H.
George H., ASE Certified Technician
Category: Buick
Satisfied Customers: 15604
Experience:  ASE Master 15+years
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I have a 99 Buick Century and the cooling fans wont come on.

Customer Question

I have a 99 Buick Century and the cooling fans won't come on.
Submitted: 4 years ago.
Category: Buick
Expert:  George H. replied 4 years ago.

Hello I will help you with your question,

 

Do the fans come on when you select AC on the climate control panel?

 

There are several reasons the fans may not be operating, the fan motors may have failed, the power supply to the fans may be open or the ground from the fans may have opened.

 

Do you have a testlight or voltmeter to make some simple tests with?

 

Is the radiator full of coolant?

 

Here is the wiring diagram for the fan circuit I will guide you to the repair if you will answer my questions.

 

graphic

 

Thank you

 

 

George H., ASE Certified Technician
Category: Buick
Satisfied Customers: 15604
Experience: ASE Master 15+years
George H. and 9 other Buick Specialists are ready to help you
Customer: replied 4 years ago.

The fans do not come on when I select the a/c.

I do have a testlight.

The radiator is full of fluid.

 

This may be a seperate issue, but the air control is not working either.

Expert:  George H. replied 4 years ago.

Great, lets get started.

 

Check at the fan connector for power between the pins of the harness side of the connector. Do this with the AC selected on and the engine running. Disconnect the fan connector before you start the engine

 

If you do not have power there move to the relay box under the hood. and pull relay #12. Plug the fan connector in and use a large paperclip to jump between pin socket #30 and #87 (they are numbered on the bottom of the relay) Turn the key to the run position and let me know if the fan runs

 

graphic

 

If the fan does run use the paperclip in pin socket #86 and run your testlight from there to ground at the battery. If the test light shows power with the key on and the AC selected let me know

 

Enough for now, do these tests and post back

 

 

 

 

Customer: replied 4 years ago.

Okay, I'm not getting power at the harness.

When I put the paperclip between #30 and #87, the fan starts running even without

turning the key.

 

I put the paperclip in #86 and touched the battery I had power.

Expert:  George H. replied 4 years ago.

Try putting the paper clip in #85 and turning the key on but put the other end of the testlight to power at the battery. If the light comes on with the engine running and the AC on the PCM is trying to turn the fan on.

 

So far you have verified that you have a good fan, fuse for the fan and wiring to the fan. Now we start to work on the system that tells the fan to turn on.

 

You said your air control does not work? The AC button does light up?

 

Try this after testing at pin #85, put the relay inplace and disconnect the coolant temp connector from the sensor and use the paperclip to jump acrosss the pins of the connector on the harness side.

 

The CTS is located here

 

This is on the drivers end of the engine just below the fuel pressure regulator and above the upper radiator hose inlet fitting to the engine.

 

Turn the engine on and the fan should run, if it does not swap relays with one of the others in the same relay box and try again.

 

Let me know what you find.

 

Sunday is "dinner" with my 93 YO mom so I will be offline for a couple of hours.

 

Let me know what you find and I will post back or I will opt out and allow other experts to continue with your question if that is what you would like

 

Thanks

 

 

 

 

Customer: replied 4 years ago.
The light doesn't come on when going between #85 and the pos battery terminal.
Expert:  George H. replied 4 years ago.

This means that the computer is not sending the nsignal to turn the fans on.

 

Try shorting the coolant temp sender as I outlined above and see if the fan will come on with the relay installed and the engine running

 

 

Customer: replied 4 years ago.
Both fans come on when I jump across the sensor.
Expert:  George H. replied 4 years ago.

OK I am back, sorry for the delay

 

Great this means that the PCM is capable of controling the fans so you have a problem with the sensor itself or the AC circuit.

 

You never told me about your statement that the air control is not working either.

 

Does the AC work?

 

Why do you believe that the fans do not work?

 

 

Customer: replied 4 years ago.

While I was waiting I went ahead and changed the CTS and it didn't make any difference.

 

The AC works some but not great.

 

When I'm talking about the air control, I'm talking about when you switch from vent, to

bi-level, max, to defrost, the air flow doesn't change. Air comes out of all vents.

 

Also, the low coolent light stays on most of the time.

 

The reason I say the cooling fans aren't working is because the car runs cool as

long as you moving. But when you come to a stop the motor starts heating up quickly.

And I've stood there with the hood open and the fans won't kick on.

Expert:  George H. replied 4 years ago.

I just lost a long answer to you,

 

You will need to get the codes read at an Autozone or other large parts store so we can find out what the PCM thinks is happening

 

Does the AC compressor run when you turn the switch on?

 

 

Customer: replied 4 years ago.

I really couldn't here the compressor come on so I added some refridgerant

and then I could definately here it kick on. Now the fans will work when the AC is on.

Expert:  George H. replied 4 years ago.

So the problem is that you have a leaking AC system. The most common leak on these is the compressor. If the body is covered with oil the compressor is leaking.

 

If you scan the computer you will see AC inhibited due to low pressure codes. The computer is never seeing the coolant get hot enough to turn the fans on. The coolant level is low enough to leave the sensor in the air or you have a bubble in the system.

 

Have you bled the air from the cooling system?

 

If not here is the procedure

 

Filling Procedure

Notice: DO NOT use cooling system seal tabs (or similar compounds) unless otherwise instructed. The use of cooling system seal tabs (or similar compounds) may restrict coolant flow through the passages of the cooling system or the engine components. Restricted coolant flow may cause engine overheating and/or damage to the cooling system or the engine components/assembly.

  1. Close the radiator drain valve. Install all the engine block drains.
  2. Remove the coolant recovery reservoir and empty. Flush the reservoir with clean water, drain and reinstall. Important:
    • When refilling the engine coolant system, add GM approved new Ethylene Glycol Coolant DEX-COOL(TM) GM P/N 12346290.
    • If the cooling system is being refilled ONLY (no flush), a 50 percent ethylene glycol and 50 percent clean water mixture should be used to fill the system. Fill the system until the level of the 50/50 mixture has reached the base of the radiator neck. Wait two minutes and recheck the level of the coolant mixture, add a 50/50 ethylene glycol/water mixture as necessary to restore the coolant mixture level to the base of the radiator neck.
  1. Slowly fill the cooling system through the radiator neck using the following procedure:

3.1.If the coolant system has been flushed first add 100 percent ethylene glycol in the amount listed for the appropriate engine application.
3.2.Slowly add clean water to the system until the level of the coolant mixture has reached the base of the radiator neck.
3.3.Wait for two minutes and recheck the level of the coolant mixture, add clean water if necessary to restore the coolant mixture level to the base of the radiator neck.

  1. Install the radiator cap making certain the arrows line up with the overflow tube.
  2. Close all air bleeds. DO NOT over-torque the air bleed valve. The air bleed valve is made out of brass.
  3. Add 0.75 liters (0.80) quarts) of a 50/50 mixture of ethylene glycol and clean water to the coolant recovery reservoir. Notice: The Low Coolant warning/indicator lamp may come on after this procedure. If after operating the vehicle so that the engine heats up and cools down three times, the Low Coolant warning/indicator lamp does not go out, or fails to come on at the ignition check, and the coolant is above the full cold mark in the reservoir, refer to Low Coolant Warning/Indicator Lamp in Instrument Panels, Guages and Warning Indicators. If at any time the Temperature warning/indicator lamp comes on, immediate action is required. Turn OFF the engine and allow the vehicle to cool. Do not remove the coolant recovery reservoir cap at this time.
  4. Inspect the freeze protection of the engine coolant after the engine heats up and cools down three times using a refractometer or a hydrometer to ensure proper freeze -37°C (-34°F) protection. Obtain the coolant mixture for the inspection from the base of the radiator neck, NOT from the coolant recovery reservoir.

The air bleeds are on the inlet next to the end of the hose

 

graphic

 

You can also remove a lot of air by running the engine at 3000 RPM with the cap off and filling as it is running but you will have to bleed the air until only coolant runs from the air bleed

 

 

Customer: replied 4 years ago.

I have bleb the cooling system in the past but have not done it recently.

 

If the refridgerant is low, wilthat effect the operation of the air flow switch, (i.e. vent, defrost, htr?
Expert:  George H. replied 4 years ago.

Try bleeding it now and let it run til the gauge shows 3/4 hot then see if the fans cycle on.

 

The airflow problem is not related but you will have to tell me if this is an automatic temperature control system or is this manual?

 

 

Customer: replied 4 years ago.

Honestly I'm not sure. It has temp adjustment knob between the fan control and the

airflow knob.

Expert:  George H. replied 4 years ago.

This is the manual system the automatic has a display that you set the temp on.

 

The air doors are vacuum controled so you will have to check the vacuum supply to the control head (black hose) then connect the vacuum supply to the various vacuum motors to see if they move while the engine is running. You will be taking the place of the control head. If all of them work the control head is the problem

 

Here is the diagram of the vacuum routing there is a vacuum connector under the center of the dash just to the right of center this is a good place to check for supply while the engine is running and to use a small hose to jump the vacuum to the different colored hoses shown in the diagram with the blower running then you can feel for the air from the vents

 

graphic

 

 

 

 

Customer: replied 4 years ago.

I'll let you go. I'm going to bleed the system and see how that works.

 

I appreciate all your help.

Expert:  George H. replied 4 years ago.

Glad to help and I will watch for your post. Have a good night!

 

 

Customer: replied 4 years ago.

Hi George, I bled the system and that seems to have solved my problem for now.

 

I must have a leak in the cooling system somewhere because I continue to

smell anti-freeze. I've check everything I can see and haven't found anything.

I also got the air flow problem fixed. It ended up being a cracked vaccum hose.

 

Thanks again for all your help.

Expert:  George H. replied 4 years ago.

Glad you got it working, if you continue to get air in the system you may have a leak in the intake gasket area. The smell of coolant will last a long time so it may just be leftover coolant and it will have to run off over the next few weeks. Keep an eye on it.

 

Thanks for using JA!!

 

 

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