Heater Craft heater

Tom,
When you got the zero volt readings, did you check the volts going into the switch? There should be one terminal that's always got the volts and then depending on the switch position the current gets sent to the respective low, med., high terminal. Check the switch again for volts going into the switch. If nothing, then there's a problem upstream like a connection or a bad breaker. If you have power going into the switch but noting out at any of the 3 settings, then the switch is bad.

Tom,
Here's a picture I found of the 4 position Heatercraft switch:



Isn't there a 4th terminal for the 12 volt supply?

Yes, that is my switch, and the wiring seems to be what the manual states. The heater did work great for four seasons. One thing I just noticed as I was tracing the black ground wire behind the dash is that it ends, and is spliced into a wire that goes to the cigaret/phone charger plug in (for lack of a better term). Anyway, that connection/splice looks really bad. Exposed wire, and some corrosion. I have no idea if that means anything or not, but thought I'd mention it.

I'll double check for more corrosion. Sorry I'm so ignorant about electrical topics, but since you have the photo of the switch I can tell you exactly what I did with the VOM. I placed one probe on the somewhat isolated terminal (and kept it there), and the other on one of the three terminals that are kind of grouped together. As I went from one terminal to the next (while keeping the first probe on the isolated terminal) I always got 12.3 volts on the VOM as long as the switch was in the "off" position. Zero volts all around if the switch was in any other position. Does that mean there are 12 volts at the switch?

OK, will try and do that. The black ground wire goes from the cigaret lighter to the blower/main heater unit. It doesn't get anywhere near the switch. What should I put the probes on?

OK, I think I managed to do as instructed. Slightly pulled back the ground on the terminal at the cigaret lighter to expose more metal, and placed the black probe on the terminal. Next, with the switch in the "off" position (but the accessory one pushed on) I put the red probe on the four terminals of the rotary switch. It read 12.4 volts at the isolated terminal and a few mV on the other terminals. In every "on" position it was reading 12.4 volts at all four terminals. On a side note, did I hear your families name mentioned on the local news for putting on the festival of lights in Three Lakes?

Tom,
We may be getting someplace now that I think you found an actual ground and not a 12 volt positive.

Follow the wire connected to the 12 volt supply to the switch (you call it the "isolated terminal") back to the breaker which you have said is accessory 1. Turn the selector switch to any position (low, med. high) where you are getting the 0 volt readings. Keeping the black probe of the VOM on the ground use the red probe to check for volts both in and out of the accessory 1 breaker. You should only have 2 terminals on the breaker. 1 is the "load" going to the blower selector switch and the other is the 12 volt source. Report back.

I'll do that breaker test later today. I'm stuck at work this weekend, so I'll report back this evening. Thanks again for the patience.

KENO wrote: Hi Tom Your "isolated terminal" is power into the switch like Pete has said. It sounds like you have 12 volts there and at your accessory 1 breaker.based on what you've posted already .

Ken,

tjs1295 wrote: The only time I saw a reading (which was 12.1 volts) was with the switch in the off position on the isolated terminal. .

Tom has mentioned no volts at the switch supply when the switch is turned to any of the speeds twice so, I'm taking him upstream to testing the breaker and I have mentioned checking connections. I have a feeling with an applied load, a bad connection or bad contacts in the breaker is pulling the volts down.

BTW, I might have to make a "house call" on this one!! And, I won't be coming down a chimney!!

You only got 12V once because it looks like you are measuring across the contacts of the switch,
If you put one lead on the incoming (isolated terminal) and the other on any of the three outgoing leads (to the fan) you should get 12V to ground on the isolated one, and 0 on all the others when you put the switch in one of the running positions. If you are measuring each outgoing terminal to ground you should see 0V to ground on the three outgoing terminals with the switch in OFF and 12V to ground on each terminal when the switch is in the position that corresponds to that terminal but you will see 0 Volts between the isolated terminal and the selected terminal because you are now looking at the voltage drop across the contact instead of seeing if power is actually there or not. If you are looking for the presence of power at a location in the circuit always measure between the circuit and a good ground. After you find out where the volts disappear you can start measuring across contacts, and connections to see what part is bad.

When the switch if off you have 12V on the incoming power line, when the switch is in any other position that contact for that speed is closed and you will have 12V minus any contact resistance. ie if you put the switch in low and measure from incoming terminal to the low speed terminal you now have a reading of 0V between the incoming lead and low speed lead because you are measuring across the contact in the switch. If you measure from the low speed terminal to ground you will now have 12V.   

You need to measure from each terminal to ground (which I think you already did.) It looks like you have 12V going to the motor from the switch so there is either a really bad ground connection, an open circuit in the unit itself, or the motor is bad. Since it doesn't work in any speed my bet would be on a bad ground connection.

If you measure 12V to a good ground with the switch off, and then move the switch to any running position and that voltage drops way down it could indicate a bad power side connection (high resistance hot side connection somewhere. If it doesn't change at all then its an open circuit somewhere after the switch.

You are seeing 12V on all the outgoing leads because the motor only has 2 connections (line and ground) and the voltage (but no current) from one closed contact is back feeding back up to the other two open contacts in the switch. The switch contains 2 different resistors and one direct connection that limits the current flow to the fan (and/or drops the available voltage) to give you the three different fan speeds.

Think of the switch as 3 different sized pipes with valves in them. The pipes are 2 4 and 6 inches in diameter all sitting on the ground next to one another connected to the bottom of a water tank. You fill the tank quickest from the 6" pipe but all the pipes or full of water on the back side of the valves. That's why the switch contacts all show the same voltage when any one of them are closed.

Your switch is working properly, and you have 12V through the switch. Add a temporary jumper wire from the ground wife all the way back to the negative terminal on the battery and see if that works.

Is there an inline fuse that could have blown or reset button on the blower itself?

I was typing as you responded Mark. I'll have to look for an inline fuse, or reset button.

mark c wrote: You only got 12V once because it looks like you are measuring across the contacts of the switch,

Tom wouldn't get any voltage reading at anytime if he was measuring across the switch contacts!!

Having 3 different windings in a DC motor is a very expensive way to control the speed of a motor, Maybe that's why heatercraft charges so much for their hardware. All DC fan motors similar to the ones used in cars up until the automatic ventilation systems with PWM fan control were done with 2 or 3 parallel resistors in either the armature, or field wiring to control the current to one of these sets of windings. The more resistance added to the armature windings tend to slow the motor down, and the inverse happens when resistors are added to the field wiring. Almost all small DC motors use the Armature winding scheme to control speed. Direct connection, full speed, high resistance slow speed.   If the resistors are not in the switch then they are inside the box where the Fan motor resides, at the other end of the wiring.

8122pbrainard wrote: mark c wrote: The switch contains 2 different resistors . Mark, Here's your two ceramic resistors in the air flow of the blower itself for cooling. There's NO way a tiny SP4T switch could house resistors plus cool them.

So Pete

This must be your funny way of saying that the motor doesn't have 3 different windings like you thought and like Mark said it has 2 resistors . One for low speed and one for medium speed and nothing needed for high speed