Cooling only runs when defrost is on

Tiny
JESS COLON
  • MEMBER
  • 2002 TOYOTA SIENNA
  • 200,000 MILES
My cooling fans only run low when the defrost is on. And only sometimes. The fans will not kick on by them selves and the A/C and heat does not kick them on. Only the defrost and it works sometimes and sometimes they don’t come on at all. I checked the relays and unplugged the sensor and nothing changed.
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Sunday, March 10th, 2019 AT 1:55 PM

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Tiny
JACOBANDNICKOLAS
  • EXPERT
Welcome to 2CarPros.

The first thing you should check are the coolant temperature sensors. That is what sends the signal to operate the fan other than when the AC or Defroster is on. There are two engine coolant temperature sensors (ECT).

Here are the directions for testing the sensors:

INSPECTION
1. DRAIN ENGINE COOLANT
2. REMOVE ECT SWITCHES

Picture 1

3. INSPECT NO. 1 ECT SWITCH
a. Using an ohmmeter, check that there is no continuity between the switch terminals when the coolant temperature is above 98 C (208 F).
If there is continuity, replace the switch.
b. Using an ohmmeter, check that there is continuity between the switch terminals when the coolant temperature is below 88 C (190 F).
If there is no continuity, replace the switch.

Picture 2

4. INSPECT NO. 2 ECT SWITCH
a. Using an ohmmeter, check that there is continuity between the switch terminals when the coolant temperature is above 94 C (201 F).
b. Using an ohmmeter, check that there is no continuity between the switch terminals when the coolant temperature is below 83 C (181 F).
If continuity is not as specified, replace the switch.
5. REINSTALL ECT SWITCHES
6. REFILL WITH ENGINE COOLANT
________________________________________________
If the sensors are good, then you need to check the relays. I realize you moved things around, but you need to test things to confirm.

COOLING FAN RELAY
INSPECTION
1. INSPECT NO. 1 COOLING FAN RELAY

Picture 3

a. Remove the No. 1 cooling fan relay. (Marking: FAN NO. 1)

Picture 4

b. Inspect the No. 1 cooling fan relay continuity.
1. Using an ohmmeter, check that there is continuity between terminals 1 and 2.
If there is no continuity, replace the relay.
2. Check that there is continuity between terminals 3 and 4.
If there is no continuity, replace the relay.

Picture 5

c. Inspect the No. 1 cooling fan relay operation.
1. Apply battery voltage across terminals 1 and 2.
2. Using an ohmmeter, check that there is no continuity between terminals 3 and 4.
If there is continuity, replace the relay.
d. Install the No. 1 cooling fan relay.
2. INSPECT NO. 2 COOLING FAN RELAY

Picture 6

a. Remove the No. 2 cooling fan relay. (Marking: FAN NO. 2)

Picture 7

b. Inspect the No. 2 cooling fan relay continuity.
1. Using an ohmmeter, check that there is continuity between terminals 1 and 2.
If there is no continuity, replace the relay.
2. Check that there is continuity between terminals 3 and 4.
If there is no continuity, replace the relay.
3. Check that there is no continuity between terminals 3 and 5.
If there is continuity, replace the relay.

Picture 8

c. Inspect the No. 2 cooling fan relay operation.
1. Apply battery voltage across terminals 1 and 2.
2. Using an ohmmeter, check that there is no continuity between terminals 3 and 4.
If there is continuity, replace the relay.
3. Using an ohmmeter, check that there is continuity between terminals 3 and 5.
If there is no continuity, replace the relay.
d. Install the No. 2 cooling fan relay.
3. INSPECT NO. 3 COOLING FAN RELAY

Picture 9

a. Remove the No. 3 cooling fan relay. (Marking: FAN NO. 3)

pic 10

b. Inspect the No. 3 cooling fan relay continuity.
1. Using an ohmmeter, check that there is continuity between terminals 1 and 2.
If there is no continuity, replace the relay.
2. Check that there is no continuity between terminals 3 and 5.
If there is continuity, replace the relay.

Picture 11

c. Inspect the No. 3 cooling fan relay operation.
1. Apply battery voltage across terminals 1 and 2.
2. Using an ohmmeter, check that there is continuity between terminals 3 and 5.
If there is no continuity, replace the relay.
d. Install the No. 3 cooling fan relay.

__________________________________________

Here are a few links you may find helpful:

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

https://www.2carpros.com/articles/how-to-use-a-voltmeter

https://www.2carpros.com/articles/how-to-check-wiring

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

___________________________________________

Let me know if this helps and what you find. If you have other questions, let me know.

Take care,
Joe
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Monday, March 11th, 2019 AT 4:28 PM

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