220 Volt Question

[Unimatic1140]

My '59 Philco dryer decided to stop heating last night, everything else works just fine. So tonight I took some measurements trying to determine the cause and I want to be sure I'm reading the results right.

With the dryer running when I measure from point A to ground my meter reads 122 volts, when I measure from point B to ground I also get 122 volts (see schematic below). When I place one meter probe on A and one meter probe on B I get 0 volts, I believe I should read 220 volts here.

I've tested the input of the cord at Red and Black and I do read 220 volts. I've tested both the High Limit and Control Thermostats for resistance and they both are closed and working properly at 0 ohms.

The thing that confuses me is when I measure the two heater terminals for resistance I get 9.4 ohms (after removing the connected wires from the terminal). I would think if the heater was bad or open I would get infinity resistance. Can I assume there is a problem in the heater or am I missing something? Since 120 volts gets to each side of the heater separately can I assume that it should heat at 220 volts? What do you guys think?

 

[combo52]

Dryer heat circuit testing

Disconnect wire A&B from heater terminals and test from each to ground you will not get 120 volts on one side this will help you decide witch side of the 240 volt circuit is faulty. I would bet motor centrical sw bad timer or heat control sw. Test must be done with dryer running be careful.

 

[cadman]

Robert, do you have a way to clip onto A and B and measure for 240v when running, with heater and everything else in circuit?

It's not uncommon for a heater to go open as it warms and expands; this should let us know for sure- Your meter may even jump up a few volts if the heater goes open during the test.

Cory

 

[Unimatic1140]

Hey John!

Thanks John. So I didn't realize I should remove the two wires that attached to the heater before testing, which now that I think about it makes total sense. So I ran downstairs and tried it. Unfortunately with the wires removed the Gray wire (point A) reads 122 volts, the Blue wire (point B) reads 117 volts. When I turn the heat switch to air dry, the value on the gray wire drops to 0 volts which is what I would expect and the blue wire remains at 117 volts.

Now I'm really confused lol.

 

[Unimatic1140]

Robert, do you have a way to clip onto A and B and measure for 240v when running, with heater and everything else in circuit?

Hey Cory, I did clip onto both A and B at the same time and it reads zero volts (both wires connected to heater). Let me try that with both wires removed. brb

 

[Unimatic1140]

Yup with both wires removed from the heater, one attached to each side of the meter I get 235 volts.

The heater isn't acting intermittent, it stopped cold and has not been able to start again.

 

[supremewhirlpol]

I would start with violet from motor terminal and red while the machine is on. If I read the schematic right, you should get 220V from those wires. If you don't, check motor terminal switch and each individual wire for continuity while the machine is unplugged. I hope this helps Robert.

 

[Unimatic1140]

I would start with violet from motor terminal and red while the machine is on.

Thanks supremewp, I assume you mean with the violet wire still connected to motor terminal at the same time measurement is taken?

 

[cadman]

Interesting.

Sounds to me like you've got a high resistance feed to the heater (now the question is, which side?), high enough that when the heating element is in circuit the meter shows zero, but without that low-z element in place, the lightly loading meter reads appropriately.

Have a 60w light bulb handy? Disconnect the heating element, then check from A to ground while running, then B to ground while running. The bulb should load the circuit enough to give us an idea if L1 or L2 is the culpret....

 

[supremewhirlpol]

Yes Robert, that's what I meant. Sorry, long day.

 

[Unimatic1140]

So when I connect the meter from Violet (attached to the motor terminal) and directly to the Red side of the cord, it reads 0 volts when the dryer is operating and 110 volts when the dryer is turned off.

I would think it should be reversed, no? I'm assuming the centrifugal switch shown in the schematic is drawn with the dryer turned off.

Cory I would have to build a socket device to do that, what would I expect to see with the light bulb connected to each side?

 

[cadman]

Robert,

What I'd expect is the bulb to light from ground to A or ground to B (heater out of circuit for all this). If you answer true for both all bets are off!

Hypothetically, if it lights from ground to B with dryer running and switches properly set, we can assume the path through the thermostat and centrifugal switch is OK and we can start back tracking from A up to the source using your test lamp (still referenced to ground) to find out if it's the heat switch, limit switch or timer contacts that's bad.

The idea is the lamp will pull enough current that any marginal set of contacts will reveal themselves as open whereas a meter draws in the milliamp range which still allows a continuity or voltage reading through even the highest resistance of contacts. We want that heater still disconnected as it would allow a sneak path back for your test lamp.

BTW, any old 60, 75 or 100w bulb should do. Got any porcelain sockets lying around or maybe a dryer drum lamp from a parts machine?

 

[Unimatic1140]

Thanks Cory, that makes total sense. I will build a socket tomorrow night and give it a try. I will report back with the findings. I bet you are correct in the fact that the dryer has a switch or bad terminal that's almost open but not quite!

 

[combo52]

240 dryer heat testing

connect the violet wire at the motor switch to the black terminal by passing the centrifugal sw this will make it heat. The centrifugal sw is one of the most common problems on older electric dryers. I usually install a 240 volt coil 30 amp heat relay in older electric dryers & combos that i intend to use to protect the timer , control thermostat, heat control sw, and motor cent sw etc. Its best to leave the heater box safety thermostat in the high current path in case the heat relay should ever stick.

 

[mrb627]

Control Therm

Robert,

Have you checked across the control therm to be sure it is not open? I think you are getting zero volts across the heating element because both side are on the same leg of power.

 

[Unimatic1140]

I love going home over lunch and working on machines!

you checked across the control therm to be sure it is not open
That was the first thing I checked Malcom as it is in easy access as well as the high-limit safety thermostat, both are working perfectly.

John and Cory thank you both, you are both correct.

First Cory, you are so right about the dryer having a switch or bad terminal that's almost open but not quite. The meter was being tricked!!! The light bulb test was pure genius! I used my interior dishwasher light assembly with a 100 watt bulb. Here is what happened, disconnecting the Dark Blue wire (point B) from the heater and connecting that wire to the light bulb, turned the dryer on and the bulb does not light.

 

[Unimatic1140]

Now I disconnected the wire from the heater on point A on the schematic and connected it to the bulb. Turned the dryer on and sure enough it lights!

 

[Unimatic1140]

Nice way to confuse little old me mr. meter

Just to make sure I'm not nuts (ok we all know I'm nuts, but not totally insane) I connected the meter back onto point B where the bulb did not light and sure enough the meter reads phantom voltage!!!! I wish my meter had a switch on it to add resistance to the circuit to check for this!

 

[Unimatic1140]

Now I took John's advice and placed a jumper wire on the black terminal to the violet wire and sure enough the dryer heats. Word of caution, the jumper wire is not very thick, so I only ran the dryer long enough to see the heater working, the wire would heat up very fast and burn off if I kept it running like this.

So the culprit is the centrifugal switch in the motor. Its a safety switch that doesn't allow the heater to come on unless the motor is running at full speed. Otherwise the heater could burn out if the fan is not blowing air through it.

Tonight I will take the motor and switch apart and examine the contacts, hopefully they are just dirty. More pictures to come.

 

[alr2903]

Wow, you guys could rule the world, you do know your stuff. Robert that big pulley must make the belt to what i think is the blower really go. Are philco's considered high airflow? alr2903

 

[mrb627]

Glad you found it.

Robert,

Glad you found the little bugger. And it didn't burn the house down. That would be a nightmare, wouldn't it...

Malcolm

 

[cadman]

Glad you found the culprit!