HELP! Came home to HVAC system running in fan mode, thermostat is powered off. UPDATE

[The Stigenator]

I just talked to the tech guy who came by the first time, he said the thing does not have a pitot tube as its a packaged air handling unit.

He said that he isnt sure why its blowing the heat towards teh sensor/electronics, says its most likely a problem with the burner and its going to be hard to diagnose..Says he isnt sure why its tripping, cause he isnt sure why the heat is coming back towards teh sensor and tripping it.

He suggested replacing teh entire unit, however I think its easier to do that then try diagnose the system, and I disagree with him on that, so I'll have to get a second opinion.

Any ideas what may be going with it. The unit is less than 8 years old. Installed 3/8/2005. Its a Lennox packaged air handling unit, 12GCS036X-75-5PB is the model #

 

[spidey07]

Why are you having to much trouble getting it repaired? Anytime I've needed work it's repaired the same day I call it in. For sure call somebody else.

 

[The Stigenator]

Well I am going to try get a second opinion on this.... I am going to call the guys who installed it < 8 years ago and have them have a look at it. They are expensive as a tech company and their service sucks even worse (last time I had an issue I had to wait 4 days for them to come look at it). These guys they have been responsive to come visit the home M-S. They tell you when they will arrive and arrive on time. They have been honest so far, but surely replacing the unit is not the solution.

 

[The Stigenator]

found the repair/service manual for the hvac, sure enough the problem i am seeing (system shuts off blower stays on) is part of the safety design..

I am looking at it more in detail but it sounds like replacement isnt an issue here, there is a primary and secondary sensor, when either of them trips (or opens), then the system de-energizes and then the system internal blower continues to run.

Now I wish I knew which sensor was what..

oh the service manual claims to check out the exhaust port for soot and debris and stuff and check / align the burner tubes.. so i'll be doing that..

 

[Rubycon]

Running a furnace with a bypassed high limit switch for anything outside of diagnostics is a very foolish thing to do! Definitely find someone else.

If there is suspicion that the heat exchanger's integrity may be compromised due to a long run without adequate airflow it must be tested for leaks. A leaking heat exchanger is extremely dangerous!

If you are familiar with reading schematic and trace through the sequence of events from when a call for heat is initiated it's not too difficult to troubleshoot this yourself.

Any competent service person can do this and have resolution quickly...

 

[The Stigenator]

Well they had it bypassed until they could get that sensor, it wasnt in stock. It took them about 10 days to get it, however I wasnt in all of that time, and when I left I turned the heat off completely.

hopefully no damage to the Heat Exchanger due to their decision to bypass it. I do have a carbon monoxide detector between the bedrooms (close to the intake of the HVAC), hope it will catch it if there is a problem...

 

[The Stigenator]

Well the final count is that the Heat Exchanger is cracked!

Lennox will be warranting it. They will also be replacing the draft inducer / exhaust and gaskets and what not else. All total labor about $1200.
The tech said he has not seen an HE crack before in all the time he's been working as an HVAC tech. He believes that the sensor was not the cause of the original failure but for whatever reason the HE cracked. However the sensor is usually the first thing that even he would replace.

I'll have to wait 4 days before the parts arrive. Eeek!

 

[edro]

At least you're in LA, not Ohio.

We had furnace troubles last winter when it was 10 degrees outside.
We had electric heaters in all of the rooms.

 

[wirednuts]

Well the final count is that the Heat Exchanger is cracked!

Lennox will be warranting it. They will also be replacing the draft inducer / exhaust and gaskets and what not else. All total labor about $1200.
The tech said he has not seen an HE crack before in all the time he's been working as an HVAC tech. He believes that the sensor was not the cause of the original failure but for whatever reason the HE cracked. However the sensor is usually the first thing that even he would replace.

I'll have to wait 4 days before the parts arrive. Eeek!

i would question how long he has been doing it. cracked heat exchangers are not common, but not unheard of by any means.

dont feel you did anything wrong though. sounds like a manufacturer defect. likely caused by using the thinnest cheapest heat exchanger possible. maybe it was dropped before install too, who knows. but the guy passing the high limit switch and leaving it like that for over a week is not acceptable. im surprised he did that, because if your house filled with carbon monoxide not only would you be dead, he would be out of a career too.

 

[The Stigenator]

i would question how long he has been doing it. cracked heat exchangers are not common, but not unheard of by any means.

dont feel you did anything wrong though. sounds like a manufacturer defect. likely caused by using the thinnest cheapest heat exchanger possible. maybe it was dropped before install too, who knows. but the guy passing the high limit switch and leaving it like that for over a week is not acceptable. im surprised he did that, because if your house filled with carbon monoxide not only would you be dead, he would be out of a career too.

Yeah the tech who found the cracked thing was quite disgusted that the last guy let it run a few days without the safety.. its a safety thing.

 

[Ns1]

Yeah the tech who found the cracked thing was quite disgusted that the last guy let it run a few days without the safety.. its a safety thing.

So you did get a second opinion? And the second opinion found the crack?

 

[KK]

Well the final count is that the Heat Exchanger is cracked!

Lennox will be warranting it. They will also be replacing the draft inducer / exhaust and gaskets and what not else. All total labor about $1200.
The tech said he has not seen an HE crack before in all the time he's been working as an HVAC tech. He believes that the sensor was not the cause of the original failure but for whatever reason the HE cracked. However the sensor is usually the first thing that even he would replace.

I'll have to wait 4 days before the parts arrive. Eeek!

I was just about to ask what make it was. My late FIL's house has a Lennox, and that thing is a POS. It's one of those all in one system. About 3 years ago they had to replace the heat exchanger, yes it was under warranty but the labor wasn't. They have dumped a ton of money in that system,(sensors/motherboards...) and I have pretty much written off Lennox as a shitty company.

 

[The Stigenator]

I was just about to ask what make it was. My late FIL's house has a Lennox, and that thing is a POS. It's one of those all in one system. About 3 years ago they had to replace the heat exchanger, yes it was under warranty but the labor wasn't. They have dumped a ton of money in that system,(sensors/motherboards...) and I have pretty much written off Lennox as a shitty company.

yeah its an all in one system.. if I am going to throw any more $$$ into this, i am going to replace it. I am tired of things going wrong.. its eating into my play $$$$

I think the one to go with is carrier or its subsidiary companies.. or trane

 

[KK]

We just had a bryant installed in our home, and my old man had a carrier installed in his. They seem pretty decent systems and hopefully will hold up over time. My old system was a goodman and the compressor failed on it after about 7 years. Could have been caused from a leaky evaporator coil that we had fixed in 2011.