71SoCal

I've got the SPAL PWM controller with the secondary relay from DeWitts to run my dual SPAL fans. I also installed the temp coolant sensor in the passenger-side head.

For some reason, I can't seem to get this thing right. Everything is connected properly. I start the car cold, use an IR gun to monitor temp at the thermostat housing, and when it gets to 175, I press the low setting. I wait until the temp gets up to around 195, then press the second one.

Do I have to wait until the car completely cools down before retesting? When I set the high temp, I plug the fans back in to get the motor cooled back down, but both fans never seem to turn off.

When is that second fan supposed to turn off? Does it have something to do with the fact that I have a 180 degree thermostat, and I'm setting the low temp at 175? I've tried other temps (low and high) as well.

I'm not sure what to think, but I'm getting frustrated with the whole thing, and I'm close to putting the low tech fan/shroud back in.

Has anyone dealt with this problem before, or am I doing something wrong?

Thanks...

miechesa

I ran into the same problem. Set low at 160 and high at 195. Fan is always on. Engine stays at 180, Maybe because its variable speed. Low speed on both fans constant to maintain temp. Anyway I dont have a problem with them being on, drives fine.

b71vette

I am in the process of installing Dewitt's Dual Spals on my 71 vert, anxiuos to see how this works out. At$425 I hope they work as designed and both do not run all the time unless engine temp requires it.

pws69

I believe the problem is that you need to set the fan-on temp ABOVE the T-Stat. Look at it this way (this is just a simple way to understand it - hold off the flames!) - the T-stat is there to determine when the water needs to go through the radiator [because it's too hot] - the fans are there to "help" the radiator when it can't cool the hot water down by itself. The fans should come on when the temp of the water exceeds the T-stat temp.

I have the same setup you have (180 stat, Spal PWM, Dual Spals) and I had no trouble setting mine up.

Gordonm

I had the same problem. You cannot set the low setting below the Tstat rating. It will never shut off. I know I tried many different things. I have mine set at about 185 on and 200 full high. This seems to work pretty well. I just hope the rad and single fan are enough for my new motor. It kept the old one cool but it was close a few times.

CGGorman

I agree with Gordon and PWS above, but I DO have a question about the PWM controller...

I was thinking about getting one, but didn't know if I needed the extra relay or not. I've already got two relays that the original SPAL kit came with. They both tie into one 180* temp switch in the head. If I get the PWM, do I need another relay harness to control both my SPALs?

Gordonm

I don't have the instructions with me but if I remember right the wiring has a provision for the extra relay. The controller will control one fan but you need a relay for the second fan. I only have a single fan at the moment so I don't have a relay just the controller.

71SoCal

Yes, the PWM controller has an output line that I believe pulls down to signal the secondary relay. Any secondary relay could work, but SPAL's relay is rated correctly for the second fan.

BTW - Thanks guys!!! The fact that my thermostat never allows the temp to get much below 180 totally makes sense as to why the second fan never turns off. I'm guessing that the second fan will only turn off once the temp falls below the low temp.

I'm going to try it out tonight...I'll keep you posted.

0Tom@Dewitt

Spal tells me that you need at least a 20 degree differential before the fans can work. So the concept of "programable" set points is kind of misleading. I mean, what else would you have other than 200 on and 180 off.
The main features of the controller is the fact it varies the fan speed, and stages the dual fans. It also will power the fans on high with the AC turned on. But the best feature, and seldom used, is the fact the controller can use the stock gauge sending unit for feedback. Most engines don't have an extra port for installing a new sender (even though we included one) and everyone asks me where do I put the switch.
Here is a link to the spal PWM manual

PWM manual

Buffalo Dude

waterplay

Why are you saying to use the green? It looks like you can use the white? (page 8 W/O AC in my case) this is what I did BUT I still have not had the chance to try it out yet. Am I wrong with what I did or will the white work? Also if I cut and use green do I need to ground the single white? (page 6)
Thanks
Dave

71roadster

I used the stock temp sensor to drive a secondary relay that provides power to the fans. Nearly free. Sometimes people overthink things

Chris

71SoCal

I’ll tell you what guys…I’m baffled.

Last night the car was cold, I unplugged the fans, ran the car up to 185 then set the low value. The yellow light stays on to tell me that it has accepted the value, then I let the car get to 205+ and set the high value. Red light stays on and I think it’s all good. I plug the fans back in to cool the motor down, which it does, but the second fan never turns off !@$%# I quit for the night in defeat.

This morning, I decided to test it out before work. I started the car and just let it sit there and idle. I watch the thermostat temp with the IR gun and around 165 the first fan turns on for a second, then turns off! Somewhere around 180 they both turn on. I turned the car off and left for work. I’m feeling frustrated and defeated. This thing should work!

Any thoughts or ideas…

Thanks guys.

kmckiou

I installed dual Spals in my son's '73 BB. We had very similar problems, but it had nothing to do with the temperature settings. It has to do with the voltage seen at the temperature sensor. The stock alternator does not put out enough juice to feed these fans. So, you get a big voltage drop when they come on. It turns out that a voltage drop happens when the sensor sees high temperature. So, as soon as the fans come on, they stay on. The situation is even worse at idle. The voltage variation is so bad I had to take a bunch of readings at different temps and RPMs and graph it to determine where to set the fans to come on and shut off. The ultimate solution was a new 105A alternator. After I got one, all the issues went away.

Good luck!

pws69

What are you using for Temp Sensors?

71SoCal

I got the sensor and sleeve from Tom DeWitt about 2 weeks ago. I'm not sure of the p/n but Tom said it was the one. It's the one that plugs into the green/black connector.

Thanks for the alternator suggestion, kmckiou. I do actually have an upgraded 140 amp alternator. It cranks out the power...at idle it can handle both fans, headlights w/hi-beams on, and anything else I can think of...and drives them all strong.

I'm thinking about pulling the sensor w/connector still attached and boiling some water. Put the sensor in 150ish water, then start adding more hot water and see what happens. By doing so, I can remove the engine/cooling system from the picture and focus on the electronics.

I'll let you know my findings...

kmckiou

I think you are on the right track. I do suggest you clip volt meter leads on the temperature sensor to monitor/record the voltage seen at the sensor. The Spal control unit appears to be monitoring voltage levels and it seems to assume a dropping voltage equates to a rising temperature level. When you program it, you are telling the controller the voltage level to turn the fans on/off.

- Kevin

0Tom@Dewitt

You can't do that. The stock temp sender is a resistor, not a switch. It changes resistance (in ohms) and the temperature changes. This device will not operate a relay.

0Tom@Dewitt

As I said above, the senders (both GM original and Spals) are resistors. They change resistance in a super small range on ohms. This is something like .2-.4 ohms if I remember right. It has nothing to do with voltage. These controllers work very well and they are pretty simple. If 71soCal is having this much trouble my guess is you simply got a bad one.

0Tom@Dewitt

I know they say that but it's wrong. Keep in mind, this controller wasn't made for Corvettes only. It was created to be universal for every car and the senders on Corvettes have very low resistance readings.

If you want to use the Spal switch we supply, then ground the white and simply use the two wire (black and green) plug as is.

If you want to use the stock sender (and have you gauge read right) use the white wire per SPAL engineering