99 Taurus cooling fan runs only when heater is on.

[JN94]

I'm stumped on my 99 Taurus. The cooling fans runs only when the heater is turned on and over cools the engine causing loss of heat. I've replaced the thermostat and both temp sensors to no avail. Oddly the fan still works with the fuse and relays removed. Anyone have any ideas on what my issue could be ?

 

[Rand]

what setting is the heat on? floor? vent? defrost?

 

[Chris142]

Should come on with the AC compressor too.

 

[JN94]

what setting is the heat on? floor? vent? defrost?

Fan runs regardless of vent setting.

 

[JN94]

Should come on with the AC compressor too.

It does. I know it's normal for them to run on defrost also.

 

[BC1]

How hot did you let it get to determine it does not turn on? Some will get uncomfortably hot, 220ish, before the computer turns it on.

 

[JN94]

How hot did you let it get to determine it does not turn on? Some will get uncomfortably hot, 220ish, before the computer turns it on.

The fan turns on immediately regardless of engine temp. Only does that when the heater is turned on. Doesn't matter what position the vent is set on.

 

[grasscutter]

The electric cooling fan is supposed to come on full time when the AC compressor is engaged.

 

[BC1]

The fan runs with the relay out when you turn on the HVAC?. That sounds like someone has done some shady wiring. Check to make sure the relay socket pins are not melted or corroded together.

 

[JN94]

The electric cooling fan is supposed to come on full time when the AC compressor is engaged.

My problem is they run when not needed , over cooling the engine resulting in lack of heat.

 

[JN94]

The fan runs with the relay out when you turn on the HVAC?. That sounds like someone has done some shady wiring. Check to make sure the relay socket pins are not melted or corroded together.

They also work without the fuse.

 

[Tman220]

My problem is they run when not needed , over cooling the engine resulting in lack of heat.

Sounds like you need a thermostat too.

An over-zealous cooling fan wont result in a lack of heat if your thermostat is doing what it's supposed to do.

 

[JN94]

Sounds like you need a thermostat too.

An over-zealous cooling fan wont result in a lack of heat if your thermostat is doing what it's supposed to do.

Thermostat and both temp sensors are new. Heat will work fine provided I can keep the fans off.

 

[Rand]

Doesn't sound normal. Needs physical investigation.

How hot was the engine before you concluded the fans weren't working?

 

[Trav]

If you don't have one here is the fan wiring diagram.

 

[mk378]

They also work without the fuse.

The 40 amp fan fuse under the hood?
In that case as @BC1 said, someone has modified the wiring.

Note that with stock wiring, the PCM controls both fan relays. The PCM has a data link connection to the HVAC computer. It also has a direct wire from the A/C high side pressure switch. Use a scan tool to check the coolant temperature sensor reading. If the PCM erroneously thinks the engine is hot or the A/C is at high pressure, it will turn the fans on high. Whenever the A/C is engaged they come on low. This brings me to the obvious point to be sure the A/C button on the control panel is not engaged.

 

[JN94]

Doesn't sound normal. Needs physical investigation.

How hot was the engine before you concluded the fans weren't working?

Fans work. They just constantly run anytime the car is running with the heater on. Live data shows the temp drop from 213°F down to 139°F. Highest temp I've seen is 217°F.

 

[JN94]

The 40 amp fan fuse under the hood?
In that case as @BC1 said, someone has modified the wiring.

Note that with stock wiring, the PCM controls both fan relays. The PCM has a data link connection to the HVAC computer. It also has a direct wire from the A/C high side pressure switch. Use a scan tool to check the coolant temperature sensor reading. If the PCM erroneously thinks the engine is hot or the A/C is at high pressure, it will turn the fans on.

Fans still work with the 40 amp fuse removed.

 

[Rand]

Fans work. They just constantly run anytime the car is running with the heater on. Live data shows the temp drop from 213°F down to 139°F. Highest temp I've seen is 217°F.

Ok so when is the fan turn on point? Some cars it's around 220f

Unless you're walking back your first post where you say they don't.???

. The cooling fans runs only when the heater is turned on

 

[JN94]

If you don't have one here is the fan wiring diagram.

View attachment 322147

Thanks for the diagram. I'll look into the wiring.