Magic-Pak's combustion motor

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Old 02-20-18, 06:22 PM
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Question Magic-Pak's combustion motor

Hi all,

Now that I had a few visits from my HVAC guy for unrelated reasons, he commented on something. So, this is a brand new Magic Pak (model #HWC9N5511P18) and I always thought the following behavior was normal.

When the furnace is turned on, you first hear the whirring of the combustion motor. Then it shuts down. Then starts again. It may happen 2-4 times. Sometimes it only happens once, i.e. it doesn't shut down. Then the ignition starts (sort of a crackle followed by whistling), then the blower comes on. After this, for about 30 seconds to a minute, all I get is room-temp air from the registers, then all works as expected. I always thought this was normal. Sometimes the blower is running without any combustion (you can see through the unit's little window) -- not at the end of the cycle.
My HVAC said: "Hmm. This is not supposed to happen, could be the controller board or some sort of misfire/igniter issue. I will call the manufacturer."

Has anyone had this experience with these units?
Thanks!
 
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Old 02-20-18, 06:39 PM
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On a call for heat the combustion blower should start and not stop until the call for heat has ended. So yes..... that is a problem. 2-4 times.... nope..... not correct.

Crackling and whistling is the spark ignition and burner lighting.... that's normal.
Main blower is timed to come on in xx seconds after burner lights.

I've never seen or worked on a Magic Pak.
 
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Old 02-20-18, 07:12 PM
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I see, thanks. Could this be something funny with the thermostat? 3rd gen Nest here...
 
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Old 02-20-18, 07:57 PM
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Yes.... the thermostat could cause that problem since the inducer is turning on and off.
 
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Old 02-20-18, 08:20 PM
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Maybe I should start with the wiring... Can someone comment? Common wire connected, internal battery fully charged, shows 3.93V.
 
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Old 02-20-18, 09:37 PM
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That wiring is fine. The only way to truly see if it's a thermostat problem is by directly connecting the white to the red wire and seeing if the furnace starts normally.
 
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Old 02-22-18, 01:51 PM
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So, my HVAC dude and I did exactly that: pulled out the thermostat and did a direct call for heat (red wire connected to white). The furnace fired right up, nothing funny. I was informed that the thermostat is short-cycling my unit and that the warranty will be voided, unless I "throw that piece of garbage into trash where it belongs."

Should I be talking to Nest about this, or do I go straight to getting another thermostat make?
 
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Old 02-22-18, 05:12 PM
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You left a picture of a nest and wiring. Is that your actual wiring ? Do you have C wire connected in your application ? If you don't have a C connected.... it could be a compatibility issue and may require a different thermostat. If you do have a C wire connected.... I'd contact nest for a replacement.
 
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Old 02-22-18, 05:42 PM
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It appears that i do, but I don't have a voltmeter to actually confirm that it's under voltage.
 
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Old 02-22-18, 06:41 PM
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In my infinite stupidity per Nest tech's suggestion I swapped W1 and Y1 and tested heat, which I think turned the AC on in 20F temperature (the unit is in a cabinet on the patio). I turned it right off. Is this okay?
 
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Old 02-22-18, 06:46 PM
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A brief shot of A/C should be ok. Good idea swapping the W and Y. You could shut the disconnect off at the outside unit to keep it from coming on.
 
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Old 02-22-18, 06:49 PM
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I honestly didn't realize what it was she suggested, because I am not so clear on which wire does what, except C. If anything got damaged, it's on them now.
 
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Old 02-22-18, 06:54 PM
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They wanted you to swap the white and yellow wires and then put the stat into cooling mode.
 
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Old 02-22-18, 06:55 PM
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Aaaand they are suggesting to leave the C wire out...
 
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Old 02-22-18, 06:56 PM
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I don't see how that can help but it's not my decision.
If you pull the C wire out.... don't let it touch any of the other wires.
 
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Old 02-22-18, 07:01 PM
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I capped it, but on a second try I believe it cycled again.
On top of which Nest just suggested that my Magic-Pak is a heat pump and my old Honeywell thermostat is indeed switched to the heat pump / electric mode.
 

Last edited by shura; 02-22-18 at 08:14 PM.
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Old 02-22-18, 08:45 PM
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It is not a heat pump. It lacks the required O connection to the thermostat for heat pump operation. The old thermostat may have been set up like that due to how the blower turns on.

I looked up the model number you left in the other thread. That is a packaged gas heat- A/C system.
magic-pak/literature/technical-specifications/V-Series_HWC4_Tech_Spec.pdf
 
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Old 02-23-18, 12:27 PM
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It IS a packaged furnace/AC unit, yes. Overall, my conversation with their support (level 1 and senior tech) was not useful, including how they went about asking me to swap the wires. Leaving the C wire out caused the furnace to run the fan without any ignition, so I reconnected it. It short cycles like before, but eventually starts heating.
Nest is sending a replacement, but my HVAC guy is telling me to just let it go and get a different thermostat make. He believes they cheaped out on hardware and sometimes the call for heat signal cannot maintain the voltage expected by the control board of the furnace.
He also seems to agree that a brief AC run wouldn't do much harm. In his words "LOL don't do that again, the oil is very cold in that compressor."
 
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Old 02-23-18, 12:41 PM
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Most thermostats use relays for switching the output functions. Any thermostat that requires a C connection or battery type use relays. There are several power stealing thermostats... like the nest... that use electronic switching. Most systems will not be bothered by that slight drop in voltage caused by electronic switching..... but we have seen several issues here in the past where the nest was ultimately not compatible.
 
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Old 02-23-18, 12:55 PM
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Yeah, pretty much what my HVAC guy said right from the moment I wanted to install Nest. Not in those exact words, and with rich use of expletives, but the gist is what you said.
I suppose one could add some external circuitry to reduce those voltage fluctuations, but I suppose he won't bother and Magic-Pak's manufacturer already told me they will only discuss it with a certified HVAC. If you have anything in mind, especially if it is a passive circuit, I will definitely appreciate it.
 
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Old 02-23-18, 01:31 PM
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A very easy work around. Requires a 24vac NO (normally open) relay. The W signal from the nest would turn the relay on an the relay would supply a hard contact to the furnace.

There are many 24vac relays you can use. Absolutely non critical.
Here's a diagram I supplied here for a member using his relay.

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Old 02-23-18, 02:36 PM
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So, the Nest's signal controls the switch between the red and white wire, correct?
I think I'd better understand an actual electric diagram, including the AC on/off signal and everything else (there's a PhD in EE diploma somewhere in one of the drawers), but let me try to show this to my HVAC contractor, he's an actual handyman. That is, if he doesn't punch me for mentioning Nest again. Thank you.
 
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Old 02-23-18, 02:39 PM
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Instead of the nest supplying the +/- 24vac to the furnace at W for heat..... it activates the relay and the relay connects 24vac directly to the W terminal. No loss.

The Y and G have nothing to do with this.
 
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Old 02-23-18, 02:41 PM
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So those connections remain as they are, got it. Thanks a bunch!
 
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Old 02-23-18, 03:37 PM
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Old 02-23-18, 03:41 PM
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That one is fine. The load is extremely low.... maybe 250ma (1/4A) maximum.
 
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Old 02-23-18, 03:51 PM
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I think I persuaded my HVAC dude to try this one last time, because he's about to punch me from just hearing the word 'Nest'. His argument is "yes, but that piece of crap will control the relay!" Since he's so sure, here's my offer to him: if it fails with the relay, I will sell the brand new replacement they sent, and he gets half the money. I think that's fair.

I suppose I could do this on my own with the newly gained knowledge, but I don't want to lose the warranty I have with him, in case something else goes wrong with my Magic-Pak. I have a 10 year parts & labor warranty for this less than a year old install.
 
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Old 02-24-18, 11:01 PM
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Quick question: for these relays, what's the typical input tolerance? If Nest's W is unstable, how unstable does it need to be for the relay to start switching back and forth?
 
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Old 02-24-18, 11:41 PM
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I don't think you'll have any problem with the relay. It'll switch cleanly on a heat call.
 
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Old 03-01-18, 12:36 AM
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Haven't added the relay yet, but the replacement Nest causes the same behavior. On top of which energy history hasn't been uploaded in over 24 hours -- never happened with the old one. Such BS...
 
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Old 03-05-18, 04:39 PM
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Two different HVACs refused to install the relay I got. According to them, in this config absolutely nothing would change and the call for heat would be interrupted the same way as without the relay.
 
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Old 03-06-18, 04:08 PM
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There's no arguing with logic.
 
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