My garage queen is a 1989 Vette with about 57,000 miles. Recently, I noticed that the aux/condenser fan was not running when the AC was set to "ON". The function of the aux fan is to blow air into the condenser coils to reduce the head pressure in the AC compressor when the AC is turned on. In addition, the aux fans provides additional cooling for the radiator once a specific coolant temp is reached. Here are the actions I have done:
1. Hard wired aux fan and the motor is operational.
2. Replaced the aux fan relay mounted on the radiator shroud.
3. Checked all fuses and they are good.
4. Ordered a new aux fan control sensor. I do not believe a new sensor will solve my problem since my Vette has a "high flow" 160 degree thermostat.
I would appreciate any comments on this issue. In addition, I would like to replace the aux fan motor and have learned this fan motor has been discontinued.
If anyone has the GM part number for the aux fan, I would welcome this information.
Thanks in advance for your time.
Ole Sam

 

What temp are you thinking fan should run?
The aux fan should come on at 238, not when the AC is on
You want to replace aux fan after you've tested and it's working? For what?

 

Sounds like you have a misconception. The ONLY condition for the AUX fan (in front of the condensor) to run is temperature. Turning the A/C on does not force the aux fan to operate. Cruisinfanatic is correct. The aux fan comes on at 238 -- and that's it. When the sensor near #1 cylinder hits that approx temp, it closes -- grounding the circuit -- and the aux fan turns on.

FWIW...the main fan is controlled by the ECM. While monitoring the temp sensor, the ECM grounds the low-voltage side the main fan relay. That energizes the 12V side -- which turns on the puller fan behind the radiator. I think that one comes on around 224 though I don't remember the exact temp right now. (Mine is modified for lower temp turn-on)

I should add that I'm not terribly impressed by the aux fan performance. That said, you can alter it's turn-on temp by swapping the block sensor to another part#. At one point, I did a thread on this.

 

I also have a '89. I thought the one wire sensor by cylinder 1 somehow controlled the cooling fan as it's wired to its relay, and the sensor between cylinders 6-8 controlled the aux fan in front of the condenser which comes on at 238 as mentioned.

I believe the ECU controls the cooling fan based on coolant temperature and vehicle speed, but can someone clarify what the various temperature sensors for an '89 do and where they're located? Are there three temp sensors? One for the display, one for the ECU and one for the aux fan or is the display sensor the same that the ECU reads.

I also had a cooling fan issue. Mine ran all the time. Turned out that the AC refrigerant high switch sensor was dislodged. Once I reconnected it, the fan worked normally.

Can someone please summarize the various temperature sensors?

 

I told you a lot of what you need to know in my prior post. The conditions stated for the aux fan are complete and true. Because this thread was about Sam's AUX fan, I tried to address that -- w/o getting overly detailed on the main fan. There are a few "logic" points for the main fan I'll try to describe for you....Everything below applies to the MAIN FAN.

There are 2 temp sensors. One of the dash (front of the intake manifold) and one for the ECM that you identified. The block SWITCH by #1 is not a sensor. It's only closed/open. Some might call that a sensor but, technically, it's not. To finish my prior post, the main fan turn-on is 226 (not 224). It turns off at 221 (220.5). Because the dash sensor isn't the same as the ECM sensor, you may see a distrepancy for on/off temps. What the dash shows will have no bearing on ECM control of the fan. If the 2 sensors are calibrated differently, your observed on/off might be different than 226/221. Turn-on/Turn-off temps are the same whether the A/C is on/off. I'm pasting the relevant MAIN FAN tables below. I pulled these from my TunerPro and referenced the stock AYPY bin. (The other numbers are what mine is set to....So note the values highlighted in yellow).

The top 4 tables confirm turn-on and turn-off temps (226/221). 3rd one down in the left column states the fan will run if the high pressure switch is on. 4th one down says it must run for a minimum of 15 seconds -- whenever triggered. The 3rd one down in the right column says the fan will run according to the fan duty cycle table -- when the speed is below 35mph. I'm not posting the duty cycle table because it says 100% for all temps. The 4th one down in the right column says the fan turn-on will lower to 11mph if the A/C is on. To summarize the last two sentences, the main fan will turn on below 11mph if the A/C is on. Between 11mph and 35mph, the duty cycle COULD be lower than 100% -- but it wasn't set to anything less. That means -- if between 221-226 engine temp, the fan will run 100% of the time below 35mph.



BTW...I believe the main fan will also run if the ECM is in fault (limp) mode. I don't know if it runs at all speeds all the time though. It might not run above 35mph? Basically, above that speed air rushing in the grill will be superior to fan operation. (FWIW, I believe that to be true above 20mph)

 

Thank you for the reply GREGGPENN, much appreciated. That was informative and helpful.

 

A few points of clarification since the fan control parameters are used a bit differently than what is implied by their naming/labeling:

With standard tuning, the main fan will run according to the variable duty cycle table whenever the coolant temperature exceeds the appropriate (A/C on or A/C off) fan on temperature (both are set to 226 °F). The main fan will be switched off 15 seconds after the coolant temperature drops below the appropriate (A/C on or A/C off) fan off temperature setting (both are set to 220 °F).

At vehicle speeds less than or equal to 11 mph, the A/C on temperature settings will always be honored independently of A/C being on or off which causes much of the confusion. Above 11 mph, the A/C on temperature settings will only be used when the A/C is actually on and the A/C off temperature settings will only be used when the A/C is actually off as expected. The fan will run according to the variable duty cycle table (100%) in both cases.

Below 35 mph, the A/C high pressure switch will activate the fan (via the ecm) independently of the coolant temperature (if not already running) and the fan will run at the fixed duty cycle setting (100%).

Above 35 mph, the fan will only run according to the appropriate (A/C on or A/C off) coolant temperature settings and will run according to the variable duty cycle prescribed by the variable duty cycle table (again 100%), so it may be switched off above 35 mph with A/C on and A/C high pressure, presuming that the coolant temperature is below the A/C on fan off setting of 220 °F. This is the only condition where vehicle speed above 35 mph may result in fan deactivation.