Harman P68 Distribution Blower Strangeness

[Biffo]

I have a 6 year old Harman P68 pellet stove that has served us well.

This season, the stove is displaying some oddness that I am uncertain where to begin troubleshooting. The stove starts fine on its own, and ramps up the distribution fan when it detects there is a fire inside the stove. The strange thing is that with the stove set to the "Max" on either Room Temp mode or Stove Temp mode, the distribution fan will turn off for roughly 5-8 minutes after running for 30 minutes. While the distribution fan is in this off state, the stove still feeds the hopper with pellets. After the 5-8 minute time-frame passes, the distribution blower starts up at full speed again for another 20-30 minutes where it'll repeat the cycle.

In previous years, the distribution blower would stay on. In the event that it helps, the room temp is 70-72 degrees when this issue begins.

Has anyone run across this with their Harman Stove? Any ideas on what to check first?

Thanks in advance for any help.

~Bob

 

[Bioburner]

Are you up against the stop on the switch?

 

[rayttt]

You could check the bearings on the fan...does the fan spin freely or is it rough moving?

Maybe theres a built in thermal shutdown on the fan, and its over heating.

From things Ive read on these forums...blower issues is usually from a bad or shakey ESP Probe in the exhaust vent.

 

[Delta-T]

the fan will shut off if the ESP probe detects that the internal temp of the machine is too cool for correct operation. this is not uncommon when the unit is burning low, with the fan set to high, could also be an indicator that your ESP probe needs some cleaning. Ash is a great insulator, couild be tricking the stove into thinking it is cooler that it really is.

 

[Lousyweather]

would love to see a DDM reading during operation and when it shuts down......otherwise, its just conjecture

 

[Biffo]

BioBurner - I am not against the stop switch, but I did find it interesting that you brought this up. I have found that if I am up against the stop (max setting) that the stove gets wonky (surging fan speeds, etc.). So, I keep the knob backed off just short of the max fan setting.

I've cleaned the ESP probe as well thinking that it may be the cause, and still have the symptoms. I am going to show my ignorance with the following question - In regards to getting a DDM reading, is a special tool needed to pull these readings? Or can it be easily done with a voltmeter?

I did think about taking a Hell Mary approach and replace the circuit board behind the controls, and the ESP probe.

Thanks for the feedback fellows. Much appreciated.

 

[Bioburner]

DDM is a dealer tool over $300. Pot switch sounds like its going out. There is someone that repairs boards. Someone just posted getting their board fixed for an out of manufacture Harman Invincible for $125 with shipping. ESP is about $50

 

[Micmann]

I second rayttt's suggestion of thermal overload. Make sure motor is not dragging. Dust and other fibrous material can get caught in the fan or bearings could be bad. Motor heats up, thermal pops, motor stops, motor cools, thermal closes, motor runs again till it gets hot and repeats cycle. Could be something else, but this is a strong possibility.

 

[Harman Lover 007]

DDM is a dealer tool over $300. Pot switch sounds like its going out. There is someone that repairs boards. Someone just posted getting their board fixed for an out of manufacture Harman Invincible for $125 with shipping. ESP is about $50

I agree with Bioburner....sounds like a bad pot. A new board is only about $170 bucks. You can get the pots from a guy on EBay for about $10 if you are fairly good with a soldering iron.....

 

[Bioburner]

I agree with Bioburner....sounds like a bad pot. A new board is only about $170 bucks. You can get the pots from a guy on EBay for about $10 if you are fairly good with a soldering iron.....

Or we could be fighting a failing motor and have just dug up a worn pot switch that's not helping get a true fix on the problem. When was the last time the fan taken off the stove and fins cleaned and the motor windings blown out?

 

[Biffo]

Wanted to circle back on this post, and say thank you for the help and direction.
Problem ended up being the P68 Distribution blower. Must be a thermal overload switch in the blower that was causing the cycling.
I bought a new blower locally for roughly $170 after tax and installed myself. After comparing the two blowers, it was obvious that the bearings in the old blower were not working properly. The fins on the old blower certainly didn't spin as freely as the new.

After changing the blower out, no more cycling and consistent running.

Thanks again for all the help.

 

[Bioburner]

Wanted to circle back on this post, and say thank you for the help and direction.
Problem ended up being the P68 Distribution blower. Must be a thermal overload switch in the blower that was causing the cycling.
I bought a new blower locally for roughly $170 after tax and installed myself. After comparing the two blowers, it was obvious that the bearings in the old blower were not working properly. The fins on the old blower certainly didn't spin as freely as the new.

After changing the blower out, no more cycling and consistent running.

Thanks again for all the help.

Good to hear, almost three months of winter left, then another three months of shoulder season