Unexplained voltage Reading from Mastertemp 400 Blower Motor

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R

RGS1

Member
Aug 4, 2023
15
San Deigo
I suspect I have a bad motor, but wanted to check here before replacing it.
I'm getting a voltage reading Pentair tech support could not explain when I talked to them by phone. My heater will not start. After the failed starts the following are on: Service Heater, AFS LED, and the ICM LED flashes once every 3 seconds. I believe this is because the blower motor never starts, so the air flow check fails. When my heater is off, and I disconnect the blower motor connector, I get a reading of approx 120V on pin #1, which is the pin for the red wire that comes from the BM terminal (Line 2) on the Terminal board. I get a reading of 0V on Pin 3 which is the pin connected to the black F2 wire that runs to the F2 terminal on the ICM. I understand that these are the readings that would be expected. After reconnecting the blower motor connector I take an another reading from the F2 wire. To take the F2 wire reading, I disconnect the F2 wire from the F2 terminal on ICM so that I can take a reading from the end of the wire. I get a reading of approx 120V on the F2 wire, which I'm told is not expected, and cannot be explained by Pentair tech support. I'm told the F2 wire in this scenario should read 0 volts. As far as I can tell there is no short between the wires running to and from the blower motor that would cause this reading. Also, there is no continuity between pins 1 (red wire) & 3 (black wire) on the blower side of the blower motor connector when the connector is disconnected. I don't know much about motors. I asked Pentair if the reading could be caused by some sort of blower motor winding short or an issue with the capacitor(s), and they said no, and said they knew of no scenario that would cause this reading. Also, if both the F1 wire (from Line 1) and the F2 wire are disconnected from the ICM, and I take a reading between them I get approx 240V, which seems to make sense given the other readings I am getting. Earlier in my troubleshooting I tested the blower motor by touching the F1 and F2 wires when the heater was off, and the motor came on as expected. After discovering that both the F1 & F2 wires are always hot and are on different 120V phases, I retried starting the motor by touching the wires together and it started up fine and sounded normal. I can't find any wiring diagram for the motor, but Pentair tells me there is no winding that runs on 240V. Pentair only advice is to replace the blower motor, but they say they don't understand the readings I am getting.

My Mastertemp 400 is model number 460737 built on 9 Sep 2011. The blower motor assembly is GL200X30Sb (220W, 3450 RPM) and the capacitor(s) is located inside the motor housing.

All the readings above were taken with the heater off. I have not provided all the background info here, because I wanted to just focus on the blower motor for this question. Given that Pentair tech is not sure whats going on, I wanted to check here to see if anyone knows something they don't, before making the decision to put out a lot of money for a new blower motor assembly.
 
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Welcome to TFP.

Let's get some basics..

Is the red 240V plug or the black 120V plug connected in your heater?

If the blower motor spins up when you connect the F1 and F2 wires then I doubt replacing the blower assembly will fix your problem.

Read here about testing the Air Blower - Pentair MasterTemp Heaters - Further Reading

@JamesW @swamprat69 may have more ideas.
 
Is your heater wired for 240V? The contacts on the Fenwal relay for the blower motor ( F1/F2 normally open ) provide 1 leg of the power to the motor. In looking up the blower assembly from the manual https://www.pentair.com/content/dam...p/manual/Manual-MasterTemp-472592-English.pdf ( Pentair/Sta-Rite 77707-0253 Combustion Blower Kit | Parts4Heating.com) and refering to the ladder diagram on page 42 it appears that when the heater is wired for 240 volts that only 1 leg of the 240 volts is switched (through the F1/F2 contacts on the Fenwal). This means that the F2 wire on the Fenwal can be read through the motor windings as the unswitched leg (L2) of the 240 volts supplied to the motor which would show 120 volts to ground. When the heater is wired for 120 volts the L2 would be the neutral. This is one of the reasons that I don't recommend testing a 240 volt circuit to ground if you don't fullly understand the circuit connections.
 
The F1/F2 contacts on the Fenwal are supposed to close and start the blower motor when you have 24 volts between "TH" and the 24 volt ground. If you have 24 volts at these 2 points and the contacts do not close, you would need to replace the Fenwal.
 
ajw22 said:
Welcome to TFP.

Let's get some basics..

Is the red 240V plug or the black 120V plug connected in your heater?

If the blower motor spins up when you connect the F1 and F2 wires then I doubt replacing the blower assembly will fix your problem.

Read here about testing the Air Blower - Pentair MasterTemp Heaters - Further Reading

@JamesW @swamprat69 may have more ideas.
Click to expand...
The heater is wired for 240V, and the red 240V plug is solidly connected. Thanks!
 
Do the checks described in post #4.

First check for 24V between TH and GRND.

Then if you have 24V at TH check that the relay between F1 and F2 closes.
 
swamprat69 said:
Is your heater wired for 240V? The contacts on the Fenwal relay for the blower motor ( F1/F2 normally open ) provide 1 leg of the power to the motor. In looking up the blower assembly from the manual https://www.pentair.com/content/dam...p/manual/Manual-MasterTemp-472592-English.pdf ( Pentair/Sta-Rite 77707-0253 Combustion Blower Kit | Parts4Heating.com) and refering to the ladder diagram on page 42 it appears that when the heater is wired for 240 volts that only 1 leg of the 240 volts is switched (through the F1/F2 contacts on the Fenwal). This means that the F2 wire on the Fenwal can be read through the motor windings as the unswitched leg (L2) of the 240 volts supplied to the motor which would show 120 volts to ground. When the heater is wired for 120 volts the L2 would be the neutral. This is one of the reasons that I don't recommend testing a 240 volt circuit to ground if you don't fullly understand the circuit connections.
Click to expand...
What you are saying makes total sense to me, and that's also how I read the ladder diagram. However, the Pentair tech support told me otherwise. They said no winding is powered by 240V. If that were true, I'm thinking there would need be at least 2 windings each powered by a separate 120V leg (L1 & L2). If that were the case I believe the only way to complete the circuit according to the ladder diagram would be to use the grounded heater frame as the ground leg to complete the circuits like it's done with low voltage DC circuits in a car. My understanding is that would be dangerous in a high voltage application and not be permissible by code. I suspect I got bad information from the Pentair tech.
 

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swamprat69 said:
The F1/F2 contacts on the Fenwal are supposed to close and start the blower motor when you have 24 volts between "TH" and the 24 volt ground. If you have 24 volts at these 2 points and the contacts do not close, you would need to replace the Fenwal.
Click to expand...
After attempted starts, I had 24V between ground and the following points: the control board IND pin, the ICM IND terminal , and the ICM 24VAC terminal, but the fan never started. At this point I suspected the built-in ICM relay that connects The F1 & F2 terminals was bad. I ordered a new (certified used one actually) ICM and it never worked. It's a bit of a long story, so I will explain in a subsequent post.
 
The voltage selector plug changes the connections from series to parallel.

Each winding gets 120 volts either way.

In series the two windings each get 120, which adds up to 240.
 
The voltage selector plug changes the connections from series to parallel.

Each winding gets 120 volts either way.

In series the two windings each get 120, which adds up to 240.

JamesW said:
The blower has 3 sets of windings. 2 main run windings and an auxiliary start winding.

Red and blue go to one set of windings. Black and yellow go to the other set.

For 120 volts, the windings are in parallel. For 240 volts, the windings are in series.

The auxiliary start winding is in parallel with the black --> yellow winding.

Remove the capacitor and test for resistance from red to blue and black to yellow. The values should be the same.

Label the capacitor wires C1 and C2. Test from C1 to C2, C1 to black, C1 to yellow and C1 to white.

Test from C2 to black, C2 to yellow and C2 to white.

Test from each wire to the green ground wire to see if any wires are shorted to ground.
Click to expand...

JamesW said:
To test the motor directly wire as follows:

For 240 volts, Black to hot leg, Red to the other hot leg, blue and yellow connected together.

For 120 volts, red and yellow to one line, black to the other line and blue and white connected together.

Note: I think that this is right, but I can't guarantee it. It's presented as is. If you want to test like this, you do it at your own risk.

Do the resistance test first as that should tell us something.

Test the capacitance of the capacitor to make sure that it's correct.

One power leg is always connected to the blower motor and the black wire from F2 is the switched leg.

You might have gotten a power surge, but I don't know if it would affect the motor if the switched leg was not connected because the current could not flow.

I suspect that it's a board or ignition control module problem.

Either way, the recommended tests should let us know something.
Click to expand...
 
ajw22 said:
Do the checks described in post #4.

First check for 24V between TH and GRND.

Then if you have 24V at TH check that the relay between F1 and F2 closes.
Click to expand...
Thanks so much for your help. I never checked for voltage on the TH pin or terminal because I did not expect them to go hot until the AFS check was satisfied. I had assumed the startup sequence did not get far enough to activate TH because of the AFS error. As mentioned in my previous post I ordered a new ICM module because I suspected the built-in ICM relay that connects the F1 F2 terminals was bad. However, before the new ICM arrived I made a wiring change on the original ICM. The F1 & F2 wire connections were reversed on my original ICM module. The F1 wire was connected to the F2 terminal, and the F2 wire was connected to the F1 terminal. The heater had never been repaired since it was installed, so I figured it was probably wired in reverse at the factory, and that it was not a problem, since the heater worked fine for 12 years. Before changing the wires to the correct terminals, I called Pentair tech support to make sure it was OK. They told me the relay is not directional so it does not matter if the wires are reversed, but I could switch the wires to the correct terminals. I put the wires on their matching terminals to avoid any future confusion. When the new ICM arrived, I went to install it and saw that the old ICM was burnt and partially melted. I broke open the case and saw that the source of the heat was the built-in relay that was now completely cooked. I called back Pentair to reconfirm it was OK to have switched the wires. I talked to a different tech this time and they reconfirmed it was not a problem and it could not be the cause of the melted ICM. I installed the new ICM, and the heater was now completly unresponsive when I tried to start it up. No LED lights at all. I disconnected the new ICM in case it melted like the old one. This is when I took a closer look at the F1 and F2 wires, and determined that they had 240V between them. This did not jive with what the tech had said about the ICM relay only switching a 120V circuit. As mentioned in my first post, Pentair said something must be wrong with the motor if I am seeing 240 volts between the F1 and F2 wires, and the only suggestion they had was to replace the motor. I did not feel totally confident with their assessment, so that led me to post the question here. The new ICM module may be bad, or perhaps it also got cooked. At this point I want to eliminate the motor as a problem, before purchasing another ICM.
 
I want to make sure you understand the way things are operating.

The 24V at TH is what closes the relay in the ICM that connects F1 to F2 and powers the blower.

If you have 24V at TH and the relay works and closes the blower should run. You already confirmed the blower runs when F1 is connected to F2 and that is all the closed relay does.

I agree with what Pentair techs told you that the F1/F2 has no polarity and the wires can be connected either way.

What you need to look at is the amp draw of the blower motor when it runs. Do you know how to measure amps in a circuit with a multimeter or do you have a clampon ammeter? If the blower motor is drawing more amps then it should it can burn out the relay.

Did you do the following checks on the blower motor:

Remove the capacitor and test for resistance from red to blue and black to yellow. The values should be the same.

  • Label the capacitor wires C1 and C2.
  • Test from C1 to C2, C1 to black, C1 to yellow and C1 to white.
  • Test from C2 to black, C2 to yellow and C2 to white.
Test from each wire to the green ground wire to see if any wires are shorted to ground.
 
ajw22 said:
I want to make sure you understand the way things are operating.

The 24V at TH is what closes the relay in the ICM that connects F1 to F2 and powers the blower.

If you have 24V at TH and the relay works and closes the blower should run. You already confirmed the blower runs when F1 is connected to F2 and that is all the closed relay does.

I agree with what Pentair techs told you that the F1/F2 has no polarity and the wires can be connected either way.

What you need to look at is the amp draw of the blower motor when it runs. Do you know how to measure amps in a circuit with a multimeter or do you have a clampon ammeter? If the blower motor is drawing more amps then it should it can burn out the relay.

Did you do the following checks on the blower motor:

Remove the capacitor and test for resistance from red to blue and black to yellow. The values should be the same.

  • Label the capacitor wires C1 and C2.
  • Test from C1 to C2, C1 to black, C1 to yellow and C1 to white.
  • Test from C2 to black, C2 to yellow and C2 to white.
Test from each wire to the green ground wire to see if any wires are shorted to ground.
Click to expand...
Ok, thanks for the clarification. I had thought it was IND that activates the blower, and then, following a successful AFS check, TH activates the ignitor.
I do have an ammeter, and I can also check capacitance if that is necessary. How do I access the capacitor? From what I can tell, I would have to bend the metal retention tabs at the end of the motor and then remove the end cap?? Thanks!
 
RGS1 said:
I do have an ammeter, and I can also check capacitance if that is necessary. How do I access the capacitor? From what I can tell, I would have to bend the metal retention tabs at the end of the motor and then remove the end cap?? Thanks!
Click to expand...

You check the capacitor using the ohmeter resistance, not ammeter.

Separately you should check the amp draw of the blower and see it is within the specs of the blower motor. If the amp draw is high it would be the reason the ICM relay is burning out.

I have not needed to get that deep into my heater to see exactly how the blower motor and capacitor is accessed.
 

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