Cooling fans rear intake temp switch
10-11-2017, 11:37 AM
#1
Three Wheelin'
Thread Starter
Cooling fans rear intake temp switch
After running my 1990 for an hour or so, fully warm, after full shut down, my cooling fans also shut off (not running AC).
But if I turn the ignition switch to "on" the fans run. Assuming that something is telling the fans to cool the engine off, so why don't the fans continue to run with key off?
Are there 2 different sensors communicating with the fans? and if so, they must be set at different temp levels?
But if I turn the ignition switch to "on" the fans run. Assuming that something is telling the fans to cool the engine off, so why don't the fans continue to run with key off?
Are there 2 different sensors communicating with the fans? and if so, they must be set at different temp levels?
10-11-2017, 12:37 PM
#2
Rennlist Member
There are two different scenarios as far as the fan controllers are concerned and one is what happens when the motor is running and the other what happens when the engine is switched off.
Each of these two scenarios has different possibilities.
1. When the engine is running the fans are controlled considering coolant temperature, a/c system pressure and in the case of auto transmission models the ATF temperature. The cooling system and the a/c pressure have senders so the output is modulating. The ATF is switch- on or off. Thus the fans will run at whatever voltage is required to satisfy the biggest demand.
2. When the engine is stopped. This is where either the intake switch controls or the coolant temperature controls. When both of these inputs drop to about 83C the fans stop running.
Each of these two scenarios has different possibilities.
1. When the engine is running the fans are controlled considering coolant temperature, a/c system pressure and in the case of auto transmission models the ATF temperature. The cooling system and the a/c pressure have senders so the output is modulating. The ATF is switch- on or off. Thus the fans will run at whatever voltage is required to satisfy the biggest demand.
2. When the engine is stopped. This is where either the intake switch controls or the coolant temperature controls. When both of these inputs drop to about 83C the fans stop running.
10-11-2017, 12:59 PM
#3
Three Wheelin'
Thread Starter
thanks Fred
but..........the intake sensor is measuring intake air temp and not water temp?
so in theory, with the key on and the water temp up, fans would run and then shut down with key off? and not run because intake air temp is not high enough?
but..........the intake sensor is measuring intake air temp and not water temp?
so in theory, with the key on and the water temp up, fans would run and then shut down with key off? and not run because intake air temp is not high enough?
10-11-2017, 01:25 PM
#4
Chronic Tool Dropper
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Fred nailed the functions perfectly. Expanding on his explanation a little:
-- The sensor for coolant temperature is at the front of the discharge (left) radiator tank at the bottom. That's the driver's side tank on US LHD cars. The sensor is hard to see from the top as the AC condenser is in the way, as it sits below and to the rear of the condenser there. It's easier to see looking through the grill in front.
There's a two-pin connector there that is sometimes forgotten when servicing the engine in front (timing belt service) or otherwise removing the radiator. The signal through that sensor is a very low current, so having clean connections and a good sensor is imperative. Many recommend using DeOxit spray in the connector to clear any oxidation.
Know that the failure mode on the fan controls has the fans running when that sensor loop fails open or shorted. There's a test protocol in the workshop manuals IIRC that uses your DMM in Ohms mode, testing from the fan controller connections under the cover next to the passenger's seat. Regardless of that though, you'll want to clean and firmly seat the connector at the radiator temp sensor as a logical first step, and see if that solves the symptom.
-- For others playing along or reading this later: I was just working on the temperature switch on the auto trans a couple days ago, chasing a leak I caused a few weeks ago related to that switch and another task. I grabbed some dimensions from the switch, and noted that the temperature stamped in the shell is 110ºC. I assume that the switch closes at that temperature, opens again at a somewhat lower temp. The switch is at the rear of the transmission cooler line connection on the forward left-hand side of the transmission.
For the OP, this switch is not related to your fans running at least as you describe the conditions. The transmission fluid and intake manifold switches cause fans to run on low speed regardless of key position. Since your description says it happens immediately on key-on, the suspects list is narrowed to that temperature sensor or the refrigerant pressure and AC run status.
Continuing:
-- As far as the AC and refrigerant system pressure, on my car there's enough static pressure in the system to run the fans immediately on key-on if the AC button is depressed .or. the defrost function is enabled at the dash controller. Full-defrost runs the AC compressor to dehumidify the air circulated to the glass. You can look at your controls, and you may want to confirm that the AC compressor clutch isn't engaged as you turn the key to on. Have your trusty assistant cycle the key a few times with the hood raised, while you watch and listen for the AC clutch to engage. It makes a pretty heavy clunk as the floating center of the clutch is pulled back against the drive pulley. Belt-driven AC compressor is low on the passenger's side (on US LHD cars) of the engine. No need to start the engine; the clutch will clunk with key transition from position 1 (accessories) to position 2 (engine run).
HTH!
-- The sensor for coolant temperature is at the front of the discharge (left) radiator tank at the bottom. That's the driver's side tank on US LHD cars. The sensor is hard to see from the top as the AC condenser is in the way, as it sits below and to the rear of the condenser there. It's easier to see looking through the grill in front.
There's a two-pin connector there that is sometimes forgotten when servicing the engine in front (timing belt service) or otherwise removing the radiator. The signal through that sensor is a very low current, so having clean connections and a good sensor is imperative. Many recommend using DeOxit spray in the connector to clear any oxidation.
Know that the failure mode on the fan controls has the fans running when that sensor loop fails open or shorted. There's a test protocol in the workshop manuals IIRC that uses your DMM in Ohms mode, testing from the fan controller connections under the cover next to the passenger's seat. Regardless of that though, you'll want to clean and firmly seat the connector at the radiator temp sensor as a logical first step, and see if that solves the symptom.
-- For others playing along or reading this later: I was just working on the temperature switch on the auto trans a couple days ago, chasing a leak I caused a few weeks ago related to that switch and another task. I grabbed some dimensions from the switch, and noted that the temperature stamped in the shell is 110ºC. I assume that the switch closes at that temperature, opens again at a somewhat lower temp. The switch is at the rear of the transmission cooler line connection on the forward left-hand side of the transmission.
For the OP, this switch is not related to your fans running at least as you describe the conditions. The transmission fluid and intake manifold switches cause fans to run on low speed regardless of key position. Since your description says it happens immediately on key-on, the suspects list is narrowed to that temperature sensor or the refrigerant pressure and AC run status.
Continuing:
-- As far as the AC and refrigerant system pressure, on my car there's enough static pressure in the system to run the fans immediately on key-on if the AC button is depressed .or. the defrost function is enabled at the dash controller. Full-defrost runs the AC compressor to dehumidify the air circulated to the glass. You can look at your controls, and you may want to confirm that the AC compressor clutch isn't engaged as you turn the key to on. Have your trusty assistant cycle the key a few times with the hood raised, while you watch and listen for the AC clutch to engage. It makes a pretty heavy clunk as the floating center of the clutch is pulled back against the drive pulley. Belt-driven AC compressor is low on the passenger's side (on US LHD cars) of the engine. No need to start the engine; the clutch will clunk with key transition from position 1 (accessories) to position 2 (engine run).
HTH!