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Cooling fans high speed

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How to replace coolig fan sending unit on a 2008 chevy uplander


Why ? Did you test ? Hook up a scan tool to see if the PCM/ECM - engine computer is reading coolant temp. ? Testing not guessing ? Do you even know how the system works .

The engine cooling fan system consists of 2 electrical cooling fans and 3 fan relays. The relays are arranged in a series/parallel configuration that allows the engine control module (ECM) to operate both fans together at low or high speeds. The cooling fans and fan relays receive battery positive voltage from the underhood fuse block.
During low speed operation, the ECM supplies the ground path for the low speed fan relay, which is Fan 1 Relay, through the low speed cooling fan relay control circuit. This energizes the low speed fan relay coil, closes the relay contacts, and supplies battery positive voltage from Fan 1 Fuse 29 through the cooling fan motor supply voltage circuit to the left cooling fan. The ground path for the left cooling fan is through the Series/Parallel relay, which is the Fan 2 Relay, and the right cooling fan. The result is a series circuit with both fans running at low speed.
During high speed operation the ECM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. The ECM supplies a ground path for the high speed fan relay, which is the Fan 3 Relay, and the Series/Parallel through the high speed cooling fan relay control circuit. This energizes the Series/Parallel relay coil, closes the relay contacts, and provides a ground path for the left cooling fan. At the same time the Fan 3 Relay coil is energized, the relay contacts close to provide battery positive voltage from Fan 2 Fuse 33 on the cooling fan motor supply voltage circuit to the right cooling fan. During high speed fan operation, both engine cooling fans have their own ground path. The result is a parallel circuit with both fans running at high speed.
When the request for fan activation is withdrawn, the fan may not turn OFF until the ignition switch is moved to the OFF position or the vehicle speed exceeds approximately 10 mph. This is to prevent a fan from cycling ON and OFF excessively at idle.

Feb 27, 2017 | 2008 Chevrolet Uplander

1 Answer

Fan is not working on 2001 Chevy Silverado 2500 truck radiator fan motor?


The engine cooling fan system consists of 2 electrical cooling fans and 3 fan relays. The relays are arranged in a series/parallel configuration that allows the powertrain control module (PCM) to operate both fans together at low or high speeds. The cooling fans and fan relays receive battery positive voltage from the underhood fuse block.
During low speed operation, the PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. This energizes the low speed fan relay coil, closes the relay contacts, and supplies battery positive voltage from the low fan fuse through the cooling fan motor supply voltage circuit to the left cooling fan. The ground path for the left cooling fan is through the cooling fan s/p relay and the right cooling fan. The result is a series circuit with both fans running at low speed.
During high speed operation the PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. After a 3 second delay, the PCM supplies a ground path for the high speed fan relay and the cooling fan s/p relay through the high speed cooling fan relay control circuit. This energizes the cooling fan s/p relay coil, closes the relay contacts, and provides a ground path for the left cooling fan. At the same time the high speed fan relay coil is energized closing the relay contacts and provides battery positive voltage from the high fan fuse on the cooling fan motor supply voltage circuit to the right cooling fan. During high speed fan operation, both engine cooling fans have there own ground path. The result is a parallel circuit with both fans running at high speed.
Your best bet would be to take your vehicle to a qualified repair shop !
Relay Driven Dual Cooling Fan Diagnostics

Aug 19, 2016 | 2001 Chevrolet Silverado 2500

1 Answer

I have an 05rendezvous,need to locate switches for cooling system,fans aren't co ming on & now I'm going to need a new radiator,cuz plastic broke.But it broke before fans gave out.Which I changed stat


The engine cooling fan system is controlled by the body control module (BCM) and the powertrain control module (PCM) or engine control module (ECM). The BCM performs the calculations as to how long, when and what speed the cooling fans should turn on. The BCM then sends a class 2 message to the PCM/ECM to engage the cooling fan relays. If there is a malfunction with the BCM, the PCM/ECM will control the engine cooling fans independently. The engine cooling system consists of 2 electrical cooling fans and 3 fan relays. The relays are arranged in a series/parallel configuration that allows the PCM/ECM to operate both fans together at low or high speeds. The cooling fans and fan relays receive battery positive voltage from the underhood accessory wiring junction block. The ground path is provided at G100.
During low speed operation, the PCM/ECM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. This energizes the cooling fan 1 relay coil, closes the relay contacts, and supplies battery positive voltage from the cool fan 1 fuse through the cooling fan motor supply voltage circuit to the left cooling fan. The ground path for the left cooling fan is through the cooling fan 2 relay and the right cooling fan. The result is a series circuit with both fans running at low speed.
During high speed operation the PCM/ECM supplies the ground path for the cooling fan 1 relay through the low speed cooling fan relay control circuit. After a 3 second delay, the PCM/ECM supplies a ground path for the cooling fan 3 or S/P relay and the cooling fan 2 relay through the high speed cooling fan relay control circuit. This energizes the cooling fan 2 relay coil, closes the relay contacts, and provides a ground path for the left cooling fan. At the same time the cooling fan 2 relay coil is energized closing the relay contacts and provides battery positive voltage from the cool fan 2 fuse on the cooling fan motor supply voltage circuit to the right cooling fan. During high speed fan operation, both engine cooling fans have there own ground path. The result is a parallel circuit with both fans running at high speed.
The BCM and PCM/ECM command Low Speed Fans on under the following conditions:
?€¢
Engine coolant temperature exceeds approximately 106?°C (223?°F).


?€¢
A/C refrigerant pressure exceeds 1 310 kPa (190 psi).


?€¢
After the vehicle is shut off if the engine coolant temperature at key-off is greater than 140?°C (284?°F) and system voltage is more than 12 volts. The fans will stay on for approximately 3 minutes.

The BCM and PCM/ECM command High Speed Fans on under the following conditions:
?€¢
Engine coolant temperature reaches 110?°C (230?°F).


?€¢
A/C refrigerant pressure exceeds 1 655 kPa (240 psi).


?€¢
When certain DTCs set.


The three relays are located in the under hood fuse / relay box ! You need to have it checked for DTC'S -diagnostic trouble codes ! An you need a GM Tech 2 scan tool !
This diagnostic procedure supports the following DTCs:
?€¢
DTC P0480 Cooling Fan 1 Relay Control Circuit


?€¢
DTC P0481 Cooling Fan 2 and 3 or S/P Relay Control Circuit


?€¢
DTC P0691 Cooling Fan 1 Relay Control Circuit Low Voltage


?€¢
DTC P0692 Cooling Fan 1 Relay Control Circuit High Voltage


?€¢
DTC P0693 Cooling Fan 2 and 3 or S/P Relay Control Circuit Low Voltage


?€¢
DTC P0694 Cooling Fan 2 and 3 or S/P Relay Control Circuit High Voltage


  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, command the Fans Low Speed ON and OFF.
Do the low speed engine cooling fans turn ON and OFF with each command?
Go to Step 3
Go to Step 4

3

Important:: A 3 second delay occurs before the powertrain control module (PCM)/engine control module (ECM) changes the cooling fan speed.
With a scan tool, command the Fans High Speed ON and OFF.
Do the high speed engine cooling fans turn ON and OFF with each command?

Aug 08, 2015 | Cars & Trucks

2 Answers

2004 Chevy Monte Carlo 3.4 the a/c stopped blowing,then it started overheating to the red within a couple miles,replaced the thermostat,the relay switch some days it overheats sometimes it runs fine


Are the cooling fans coming on ? What relay switch did you replace ?
The BCM will request low speed cooling fan operation from the PCM under the following conditions:
?€¢
Engine coolant temperature exceeds approximately 103?°C (217?°F).


?€¢
When A/C is requested and the ambient temperature is more than 10?°C (50?°F).


?€¢
A/C refrigerant pressure exceeds 1310 kPa (190 psi).


?€¢
After the vehicle is shut off if the engine coolant temperature at key-off is more than 117?°C (243?°F) and system voltage is more than 12 volts. The fans will stay on for approximately 3 minutes.


The engine cooling fan system consists of 2 electrical cooling fans and 3 fan relays. The relays are arranged in a series/parallel configuration that allows the PCM to operate both fans together at low or high speeds. The cooling fans and fan relays receive battery positive voltage from the engine wiring harness junction block. The ground path is provided at G101.
During low speed operation, the PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. This energizes the FAN CONT #1 relay coil, closes the relay contacts, and supplies battery positive voltage from the FAN CONT #1 fuse through the cooling fan motor supply voltage circuit to the right cooling fan. The ground path for the right cooling fan is through the FAN CONT #2 relay and the left cooling fan. The result is a series circuit with both fans running at low speed.
During high speed operation the PCM supplies the ground path for the FAN CONT #1 relay through the low speed cooling fan relay control circuit. After a 3-second delay, the PCM supplies a ground path for the FAN CONT #2 relay and the FAN CONT #3 relay through the high speed cooling fan relay control circuit. This energizes the FAN CONT #2 relay coil, closes the relay contacts, and provides a ground path for the right cooling fan. At the same time the FAN CONT #3 relay coil is energized closing the relay contacts and provides battery positive voltage from the FAN CONT #2 fuse on the cooling fan motor supply voltage circuit to the left cooling fan. During high speed fan operation, both engine cooling fans have there own ground path. The result is a parallel circuit with both fans running at high speed.
Is your vehicles check engine light lit ?
Is the

Jul 10, 2015 | Cars & Trucks

1 Answer

My ac is not working I have a Chevy Tahoe 2005 the fans won't turn on either .


Hi Maria , The A/C system wouldn't keep the fans from running but none working cooling fans will keep the A/C from working ! This is a fairly complex system if your not familiar with this sort of thing ! I will add the description from the factory service manual.
Cooling Fan Control - Two Fan System
The engine cooling fan system consists of 2 electrical cooling fans and 3 fan relays. The relays are arranged in a series/parallel configuration that allows the powertrain control module (PCM) to operate both fans together at low or high speeds. The cooling fans and fan relays receive battery positive voltage from the underhood fuse block.
During low speed operation, the PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. This energizes the low speed fan relay coil, closes the relay contacts, and supplies battery positive voltage from the low fan fuse through the cooling fan motor supply voltage circuit to the left cooling fan. The ground path for the left cooling fan is through the cooling fan s/p relay and the right cooling fan. The result is a series circuit with both fans running at low speed.
During high speed operation the PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. After a 3 second delay, the PCM supplies a ground path for the high speed fan relay and the cooling fan s/p relay through the high speed cooling fan relay control circuit. This energizes the cooling fan s/p relay coil, closes the relay contacts, and provides a ground path for the left cooling fan. At the same time the high speed fan relay coil is energized closing the relay contacts and provides battery positive voltage from the high fan fuse on the cooling fan motor supply voltage circuit to the right cooling fan. During high speed fan operation, both engine cooling fans have there own ground path. The result is a parallel circuit with both fans running at high speed.
Do you have a check engine light lit ? The thing to do would have it check at the dealer or a ASE certified repair facility ! They could hook up a advanced scan tool an diagnose fairly quick ! Or you could find a wiring diagram an try testing with a volt meter yourself ! But watch yourself so you don't short out the PCM - engine computer !

May 01, 2015 | AC Cars & Trucks

1 Answer

Cooling fan relay location


cooling fan is activate for many reasons like engine hot, A/C high pressure, if there engine code and so on
does check engine light is on?????
hope it helps

Mar 31, 2014 | 2006 GMC Sierra 1500 2WD

1 Answer

Furnace transformer/fan-relay wiring to fan-motor


All you need is 2 fan speeds, 1 for cool and 1 for heat. Leave the low speed disconnected. Normally we have high speed for cooling, and med. or low for heat. So either speed connected to the heating circuit is fine.

Apr 12, 2017 | Heating & Cooling

1 Answer

High low fan motor


Your main concern is the temperature difference across the indoor coil for both heating and cooling. When you turn your thermostat from auto to on, you are on high speed.

If you have long duct runs and little return air registers then high speed
would help cool the house better. However in the heating mode, you
could lose up to 10degrees by having the high speed setting.

What they installed is sized for your house and the speeds should not have to be changed unless the ductwork is not sized right for the house.
Cooling should be High-Black wire.
Heating should be Low-Red Wire.

400cfm equals a ton of cooling= 1200 sq. foot, For cooling you need
High speed. For heating it is whatever the temperature rise across the
coil is, which is located on the furnace/air handler.

Jul 13, 2010 | Goodman CLQ36AR49 Air Conditioner

1 Answer

Overtemp


The cooling fan is probably not working. Unit will overheat. Check the fan to see if it run continuously with no scraping noise with the UPS turned "ON". If the fan does not run, open the case and replace the fan.

Jan 19, 2010 | Powerware 9120 UPS System

1 Answer

Red light...


Red Led Is For Overtemp Condition Detected,
I Never Leave Mine In The Car Window or near the
Heater Vents.
LCD Screens are not ment to be left inside vehicles
in cold climates.
LCD {Liquid] Just like cell phones, laptops,ect
Will Mess The LCD Up.

Sep 21, 2009 | Digital Video Systems Plenio VXA-3000 GPS...

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