Lennox Pulse 21 Fan Control

[John]

I'm trying to troubleshoot the following problem with my Lennox Pulse

21 furnace: the furnace fan will sometimes shut off in the middle of a cycle (while the gas is still on and the furnace is pulsing). Occasionally this will continue until the limit is hit. The furnace has a honeywell fan/limit control but only the limit side is used... I'm assuming that the blower motor is controlled elsewhere.

I've already tried replacing the fan relay but that did not solve the problem. Can anyone provide some insight as to how the blower motor is controlled in the pulse 21? It seems funny that it has a fan/limit control but nothing is connected to the fan side...

[daytona°]

Plugged secondary Plugged filter Over firing Weak Fan/limit Plugged evaporator Plugged (I think it's called a blow by filter) internal

[John]

[Bob_Loblaw]

"daytona°" wrote

None of the above would cause the fan to shut down. Just the opposite. BTW, what is a "(blow by filter) internal" ???

[Bob_Loblaw]

"John" wrote

Do a little more reasearch and you'll find there were problems with the Pulse heat exchanger. You need someone who is trained to work on Pulse's in order to perform a credible test to see if the exchanger has failed. IOW, you have to know what you're doing to do it properly. This should be done every year. BTW, this has nothing to do with the fan issue.

[Noon-Air]

[Joseph]

John,

This group was never intended to be a homeowner forum (my opinion), however the fan is controlled by a timer and the fact that that is funny to you is reason enough for you to call a tech. You may also want to check on getting your heat exchanger checked, the Lennox guys say it needs to be pressure tested every four years. They also require the replacement of a couple of parts internal to the combustion process. FYI...

Joseph

[John]

Yeah, I know all about this. I've already performed a pressure check on the exchanger.

I'm pretty sure my problem is the fan timer control. I was a bit confused at first... it now seems that the fan relay is only use for AC, not heat. The fan timer controller has an internal relay for heat. Can anyone confirm that this is how the newer Pulse 21 is configured? If this is the case I'll order a new fan timer.

I was able to duplicate the problem once... the fan timer clicked rapidly before the fan shut down. Unfortunately I didn't have my DMM connected at the time so I couldn't verify the theory about bad timer control...

[daytona°]

Stick a CO tester in the exhaust and get a reading.......let me know what it is..and thing over 150 ppm is a bad heat exchanger

[daytona°]

I forget the real name, but the round white filter ....OH SHIT...I should go to the Dave site and get the name.....maybe be back

[Bubba]

Why stop now? Replace the thermostat. It's almost always the thermostat. You'll need to replace the low voltage thermostat wiring too. The new wiring has to be matched to the new stat or the electrons will get all confused and produce fault codes. Bubba

[John]

Yeah, this is pretty clear from the responses I've seen. "Call a tech" seems to be the standard. These things really aren't rocket science... I've been able to locate a service manual and parts source. I'll take things on my own from here.

[Bubba]

........and you think we care why? Dont let the door hit you in the ass on the way out. Thanks for shopping alt.hvac you cheap bastard Lemme guess..........another engineer? Bubba

[jamesgangnc]

[Bob_Loblaw]

"Noon-Air" wrote

Why would Lennox be reluctant to sell parts to a licensed professional?? I buy Lennox parts all the time, no problem.

[Bob_Loblaw]

"daytona°" wrote

Nope. Not even close. If you want to know the proper way to test a Pulse exchanger, email me.

Respectfully, Bob

[Bob_Loblaw]

"daytona°" wrote

It's an air flapper, not a filter. When you change one, look for a star marking on the two plates. They should be in the same quadrant when it's put back together.

[Bubba]

Purchase the "plug kit" from Lennox and you fill it with water. Totally stupid design and fix just like everything they do. Im sure you've all seen their heat exchanger with the nut, bolt and washer through the eyelet at the top to keep it from separating? Now they've gone to a tubular heat exchanger just like everyone else. The "Pulse".................what a joke. Bubba

[Bob_Loblaw]

Bubba wrote

I'm not a big fan of Lennox, but really, if you think about it, the Pulse was quite something in it's day. No ventor motor, 97% efficient, self sustaining ignition.... Once the other models caught up to it in efficiency, or close to it, there was no need for it anymore.

[daytona°]

Thanks for the offer, but I don't work on the POS's....and damn glad It's easier to change sections in a boiler