Mastertemp 400 transformer question

[pinch52]

Heater not working. Upon call for heat, no response(blower, ignition etc) from heater. Membrane shows a very high water temp, service system and service heater will blink red, the extinguish. Blower doesnt not turn on. I have no lights on the control board. Tried running the troubleshooting section of then manual, Heater Will Not Fire-A. It says to check For 24VAC at the transformer secondary. My question is this: Is there supposed to be 24VAC on both secondary wires? I appear to only have 24v from one of the wires, other wire shows 0v.

THanks!!

 

[Jimrahbe]

52,

Welcome to TFP... A great place to find the answers to all of your pool equipment questions..

When you measure the output of a transformer, you normally measure between the two wires on the secondary side, not each wire to ground..

Not sure about your heater, but depending on how the system is wired one side could be connected to ground.

Thanks,

Jim R.

 

[JamesW]

If the water temperature is showing high, then you need to deal with that first.

The heater won't do anything if it thinks the temperature is too high.

 

[pinch52]

Thanks for the replies guys. I will recheck the transformer voltage in the method you mentioned. Both of those secondary wires plug directly into the control board, both saying 24VAC. Attached are the wiring diagrams from the manual. For the water temperature issue, any suggestions on how to attack that? Thermistor? Thanks again.

 

[JamesW]

I don't think that it's a transformer issue.

If the water temperature is showing higher than actual, I would replace the thermistor.

I suspect that that will solve the problem.

 

[pinch52]

I agree!! Its been very rainy here lately, south of Houston TX. Someone mentioned using a hair dryer to dry off the circuit board. Tryed this, being careful not to get it too hot, and the membrane "pool on" light came on after a call for heat, so I think the transformer must be working. Still shows 126 degrees for 67 degree water. Any knowledge on the resistance values for the thermistor. Heater is a Mastertemp 400K BTU, model# 460736. Thanks!!

 

[JamesW]

It's a 10k thermistor. Just Google 10k thermistor chart for the values.

I think that 126 is the highest temperature indicting a thermistor error.

It's probably the thermistor but it could be a bad control board. So, it's worthwhile to check the resistance of the thermistor to verify.

 

[pinch52]

Cruddy thermistor was the culprit. Cleaned it and the contacts back to bare metal and heater fired up!! Thank you guys !!

 

[JamesW]

That one might not be good for long. Maybe consider getting a new one for backup.

 

[Pool Clown]

First, the picture you posted of the schematic shows printed 24VAC (right side). You will notice that it is printed right between the two lines coming in to the board, that means you will get 24V on BOTH those wires (24VAC/FS plug). IOW, put your probes on both wires, not one probe on one wire and the other probe to the chassis. The other printed 24V (on the left) is 24V that goes OUT to the ICM, but ONLY if the board says so. So, you wouldn't be getting 24V on that one because of the bad thermistor.

Second, That thermistor is done! "Cleaning" it may get it to fire several more times if that, but that thermistor, while you may not see it, is cracked, and will no longer be reporting accurately.

 

[pinch52]

Ok thanks guys. All good suggestions. I will get a new themistor.

 

[JamesW]

Based on how the thermistor looks, it's likely that you could have a problem with the high limit or AGS switch soon.

They typically correlate with the thermistor as far as corrosion goes.