Old Kenmore Clothes Dryer

[clearchris]

So, this is a very, very old dryer, and I love it. I can take it apart almost with my eyes closed, it's usually very easy to repair. Anyway, the timer module refuses to advance. I replaced the timer module with a used one (new unavailable), it worked for a few weeks, and now the new (used) timer module isn't advancing again.

I opened up the first bad timer module, and the RSI contact was pretty toasty, there was a nearby burn mark like it suffered a big arc at one point. While I had everything apart, I tested the timer motor and it appeared to work. I cleaned the RSI contact and reassembed it.

I have attached the dryer schematic, and there's a note, which seems relevant, but I don't understand what is going on. "With TM-RSI closed, timer motor does not run until a heat contact opens." Looking at the schematic, I'm completely unable to explain why one of the heat contacts opening up would make the timer motor run.

Can anyone explain this? I'm having a terrible time troubleshooting this when I don't understand the theory at work. Thanks!


IMG_20220518_180642.jpg

[keeney123]

The timer switch in the lowest circuit with the heater element is closed by a coil in the timer motor circuit when the Tm is connected to CS. When one of the heat contacts in the heat element circuit opens to control the heat in the dryer the TM returns to RSi to continue run the timing through the 240-volt circuit through the resistor and heat element. I do not see the control coils on the schematic, so I am going from prior knowledge. If you look at the table to the right it will tell you when each switch is being used for each setting. Possible cause of burn contact is resistor value being too low. That is RS to RS. Need to look up the part number and measure the resistor if you cannot see reading on the resistor. and measure out of circuit with ohm meter. I thought the switch timer was on a coil, but I believe it is indeed a manual timer. This dryer must be old I believe all the switches are mechanical switches.

[sam_sam_sam]

First of all the RSI is only active when it is in auto mode
Second of all the reason why there is a high value resistor on this circuit is because when the heater is on it does not have enough current to run the timer until it open then the current can flow through the heater element to run the timer motor

In refrigerator they do the same thing with the door heater circuit controlling some circuit which right at moment I remember the device it powers but I learn about this in a appliance repair class years ago and it was a hard for me to understand it at first

[keeney123]

Originally Posted by sam_sam_sam

First of all the RSI is only active when it is in auto mode
Second of all the reason why there is a high value resistor on this circuit is because when the heater is on it does not have enough current to run the timer until it open then the current can flow through the heater element to run the timer motor

In refrigerator they do the same thing with the door heater circuit controlling some circuit which right at moment I remember the device it powers but I learn about this in a appliance repair class years ago and it was a hard for me to understand it at first

The cs timer circuit and the heater element circuit are two different circuits one goes to 120V the other to 240V. It you go to the table to cs you will see that the timer still runs. The timer motor runs off 120V. When it connects to RSi it connects to the 240V. The 240V circuits has the heating element in series with the 120v timer motor and the resistor. Looks like all the switches are mechanical. Very old dryer. Well before the late 1980's

[sam_sam_sam]

I did remember what the device was that the door was feed from the compressor motor windings

I left something in my description about why the timer motor does not run when the heater is activated is even thought it has 240 volts and has a drop down series resistor is because it is a 110 volt timer motor and also remember that current takes path of the least resistance and when heater elements is activated it is the least resistance not the timer motor but when the heater element is not activated it is the next least in the path of least resistance

The reason why it was done this way for automatic mode back then they did not have moisture sensor like do now but the principle is basically the same in that when the drier get to temperature it then the timer runs until the temperature cools down and activates the heater element again the amount of time the timer is running in theory the drier the cloth are

You do not see this type of circuit very often and when people see this type circuit they are confused by it

[clearchris]

Originally Posted by sam_sam_sam

You do not see this type of circuit very often and when people see this type circuit they are confused by it

You can say that again! Thanks everyone, I'll check the resistor, it's quite possible it's fried or out of spec.

And yeah, it's probably from the 70-80s, possibly the late 60s. But it just works, the dryer is a monster that just does it's job. A few years back I replaced the belt, the felt seal, the rollers, and the wear parts are good to go for another 40 years.

Newer models, you hear about the drum cracking and all other kind of silly stuff because the manufacturers wanted to save a few bucks. Not this one, it's built like a tank and made to be repairable. This is the only issue that has given me grief. It's still on the original heater too. And now I have a spare timer (assume the new timer needs some contacts cleaned as well), the only really hard to find part for this machine.

[keeney123]

Originally Posted by sam_sam_sam

I did remember what the device was that the door was feed from the compressor motor windings

I left something in my description about why the timer motor does not run when the heater is activated is even thought it has 240 volts and has a drop down series resistor is because it is a 110 volt timer motor and also remember that current takes path of the least resistance and when heater elements is activated it is the least resistance not the timer motor but when the heater element is not activated it is the next least in the path of least resistance

The reason why it was done this way for automatic mode back then they did not have moisture sensor like do now but the principle is basically the same in that when the drier get to temperature it then the timer runs until the temperature cools down and activates the heater element again the amount of time the timer is running in theory the drier the cloth are

You do not see this type of circuit very often and when people see this type circuit they are confused by it

It was confusing and at first, I had thought what you said previously but, looking a little farther I saw the two voltages. I had assumed they just did not list the coils that control the switches in the schematic until I looked at the read out for what closes when. That read out is like a matric where you can read across and also read down That is when I realized all the switches are mechanical that are controlled by the operator when they turn on the settings.

[keeney123]

Originally Posted by clearchris

You can say that again! Thanks everyone, I'll check the resistor, it's quite possible it's fried or out of spec.

And yeah, it's probably from the 70-80s, possibly the late 60s. But it just works, the dryer is a monster that just does it's job. A few years back I replaced the belt, the felt seal, the rollers, and the wear parts are good to go for another 40 years.

Newer models, you hear about the drum cracking and all other kind of silly stuff because the manufacturers wanted to save a few bucks. Not this one, it's built like a tank and made to be repairable. This is the only issue that has given me grief. It's still on the original heater too. And now I have a spare timer (assume the new timer needs some contacts cleaned as well), the only really hard to find part for this machine.

That is what I miss about the old days. A piece of equipment that does its function and keeps on running. I believe this is attributed to simplicity in design and the ability to repair it.

Just make sure the resistor is the cause of the burnt contact by measuring it and then looking up the part number. The resistor would need to be lower in value to cause the contacts to burn out.

The mechanical switches are set by the operator. When the timing motor times out, they return to the original states. That is almost too simple to understand.

Also, make sure that the centrifugal motor switch is open when you first turn on the switch to RSI. Basically, you can just ohm out the centrifugal switch from the heating element to L2 with the dryer unplugged from the AC receptacle. If you read a short, then you will have to replace the centrifugal switch.

[keeney123]

Is this your timer part? This one is new.

https://www.genuineapplianceparts.co...b5cb6a07843f27