Heater Fan Switch

[stuhagen]

I am having a hard time finding the right switch for this application. The rotary switch has detents. The switch can also turn 360 as there are no stops. There are 5 speed levels. Turning the knob up appears to send a pulse or ground to the AC Amplifier and increases the speed. Same in the reverse. So I assumed it was a rotary pulse unit (w/0 switch) I purchased one of the only ones on Digikey (and one from Mouser) that fit my board. They really do not work. I may not be thinking in the right direction. I have a test box I use for testing the Heater itself. I have 5v applied one side and ground the other. I also have green/blue LEDs for testing going up (green LED flashes) and down (blue LED flashes. With this new pulse switch I got, they both flash going up and down with a slight millisecond delay. The OEM switch just flashes each LED individually going up or down. (there is no PN on the OEM switch)

This is what I bought thinking it might be correct.

**broken link removed**

Maybe it is some other type, like a momentary off set grounding rotary switch??

Anyways, I need to repair 2 Heaters foe friends and this is all I need. A new Heater is $750.

Stu

 

[tunedwolf]

This is probably off the mark, but that photo reminds me of the little ALP's volume control pots often used in Pioneer Car stereos and the like. You have checked to make sure it's not just a pot?

 

[stuhagen]

The Mouser one I tried was a ALPs brand. I have never seen a regular pot with detents. When reading the resistance between detents it goes like this in order:

1) 10k
2) 17k
3)23k
4)30K
5) 36K

Same in reverse, After the flash reading of resistance it rests at '0' continuity (in between detents). So detent-12k-open-detent-17k-open-detent 23k-open-detent, etc. Open= '0' continuity.

 

[tunedwolf]

In which case it would appear to be behaving like an actual switched resistor bank. If that's the case, it seems to be reading correctly and your heater control fault therefore lies elsewhere

Alps make pots with detents, as do a number of others, but they do not go open circuit as you turn them. They all use a simple little spring loaded ball bearing to give that "click". When I was a lad, they called it tactile feedback

 

[stuhagen]

Thanks....but I know it is the switch as it reads nearly a short across the 2 outer legs. Plus this shorts effects other switches. I installed this new switch and it did fix everything. Problem now is the actual fan speeds going up and down do not function properly. I am sure this switch sends a quick pulse of resistance to activate the speeds, but goes back to
open in between the clicks.

 

[tunedwolf]

What does a good switch read across the outer legs? If you have a buggered one, why not carefully take it apart and see exactly what it is, then you can at least duplicate it if need be Can you post a schematic of the heater control?

 

[stuhagen]

Here is the circuit as shown in the ECM manual. A "good" switch reads '0' ohms from center to each leg. My bad one reads about 400 ohms. Which causes havack with other
push button switches on the same circuit. It thinks it is getting the signal to operate a blower vent. This switch would be very difficult to open up. But I now have 2 bad ones so
maybe I will try. I found on the ALPs website a switch called a "self return" switch. The center leg of this switch is ground. So when you click "up" the resistance (or capacitance)
goes up incrementally. Click "down" it is reversed or high to low readings. Each click the fan speeds go up or down. Not in the circuit attached is the brains, or AC Condenser module.
That is what takes the command and sends it back to the motors, etc.

By installing a new 20 pulse encoder, it fixed all the issues with the other vent motors going crazy, and the fan speeds move but very intermittently. To many pulses maybe, and not enough delay time. Hence why I think this is in reality a "self return" style??

 

[tunedwolf]

Self return usually means spring loaded here, i.e. you turn it one way and when you let it go it springs back to center off. I'm still trying to determine if this is a resistor bank that is being switched, or if the whole resistance thing is just poor contact and it is indeed just a fancy center off switch. Have you tried just wiring two single pole momentary switches in series and wiring them into the heater control to see what happens? The schematic certainly indicates that this is just a single pole center off switch.

 

[stuhagen]

That is a good idea. I will take two momentary buttons tying the 2 legs together to ground. I will test to see if by pushing the buttons, fan speed will go up with one and down with other.
Question is, if this indeed works, is there such a rotary switch that fits this design. I have no other options other than to fit right in the OEM holes

 

[stuhagen]

OK I wired 2 momentary switches and they work perfectly. Question is where to find a vertical switch with the same pin configuration and size that would fit on the circuit board.
I spend an hour on Mouser and Digikey with no luck. It could be because I am looking in the wrong places. This switch appears to have a momentary ground to each of the outer
legs, where the center leg is ground. The switch has to be a spring back style, so when it is rotated either direction, it only momentarily grounds and releases. Picture above.
Also, this can rotate endlessly with small detents. Even though it only triggers 5 speeds.

 

[tunedwolf]

Try this: https://www.alibaba.com/product-detail/11mm-momentary-rotary-switch_785934498.html?s=p

There are manufacturers of this type of switch, most of them in the far east, that will sell in small quantities, a quick search of Alibaba or TaoBao etc will turn up a few.

 

[stuhagen]

Try this: https://www.alibaba.com/product-detail/11mm-momentary-rotary-switch_785934498.html?s=p

There are manufacturers of this type of switch, most of them in the far east, that will sell in small quantities, a quick search of Alibaba or TaoBao etc will turn up a few.

But they say the same as ones I have tried. They all say so many "pulses"-Detents much greater than what I think they are. Looking at the data sheet, they all show a PWM square wave the appears to be way to fast. However, I may have not bought the correct switch. This is the one I bought and it is too fast and the head unit doesn't get a long enough pulse for it to trigger the speed rotation.

https://www.digikey.com/product-search/en?x=21&y=7&lang=en&site=us&KeyWords=987-+1185-+ND

Stu

 

[tunedwolf]

Pulses certainly suggest a rotary encoder, which is not really what is shown on the schematic you posted. However, I think it may be that was what was originally fitted, just one with a suitable mark/ space ratio. If it really is just a fancy switch and not an encoder, what will be of primary importance to the heater control is that it only sees one switch operating at a time, i.e either going up or going down, an encoder, however, will pulse out in both switch poles as it is being rotated and this will definitely confuse the heater control. The link I posted suggests that they have several different types available, it may be worth shooting them a friendly email and asking them about their range, it may turn up a suitable candidate for replacement, they may even manufacture the correct switch or at least know who does