Original message
| bmac56
 |  "Goodman 100-4"
, posted Sat 15 Mar 00:51:  
My 1992 Goodman 100-4 has an intermittant problem starting. I am a new owner of this house/furnace, and of course no disclosure about this problem accompanied the sale.
The symptom is, when the thermostat calls for heat, the interposer relay is energized (this seems to be an aftermarket addition, indicating the problem was pre-existing). No activity at the furnace happens, it remains quiet. The series interlock chain to power the gas valve is open at the pressure switch at this time, as noted by my trusty DVM. The power vent motor does not start.
When in failure mode, I can usually get it to start by either cycling the thermostat off/on, or the furnace power switch off/on. The reason I am suspecting the power vent sequencer is that the power vent is required to be running to close the pressure switch, but it doesn't start all the time. The series interlock only seems to involve the gas valve control module, not the blower motor.
I am suspecting the power vent sequencer. As I do not know exactly how it works (is it an edge-triggered device missing my thermostat transition?), I am trying to learn so I can feel better about spending the money on it as a "shotgun" fix.
Any clarification would be welcome.
See http://s246.photobucket.com/albums/gg89/bmac56HVAC / for pictures.
Brian
[this message was edited by bmac56 on Mon 17 Mar 22:46] |
| Replies:
|
| yuri
| "Re(1):Goodman 100-4" , posted Sat 15 Mar 09:15
Take some digital pics of that relay and the front of the furnace and burner and circuit board. Post them at photobucket. Copy the IMG adress and post them here. Your description is way to involved to imagine without seeing the unit.
Yuri
|
| | bmac56
| "Re(2):Goodman 100-4" , posted Mon 17 Mar 22:48
Yuri,
I edited the original post instead of a follow-on post, sorry. This is just to inform you. I'll get used to the format soon!
http://s246.photobucket.com/albums/gg89/bmac56HVAC/ again, just in case.
Brian
|
| | bmac56
| "Re(3):Goodman 100-4" , posted Fri 21 Mar 02:08:
Thanks to marchvac for posting the photos here for me. The descriptions that were with them are not visible, so I will restate them:
The top pic is the power vent sequencer (PVS) and the bottom is the interposer. The interposer is just a slave relay to protect the Tstat from overcurrent, I suspect. It was here when I started, and suspect it was an attempt to solve this problem before. I'll clean it up when finished troubleshooting.
The PVS is what I suspect of not always allowing the power vent to operate, which has to happen before the gas valve opens and is lit, providing the heat source.
Do these PVS devices "give up" after a try if not sucessful? I have not seen it do this, but cycling the Tstat or furnace power seems to jump-start the furnace when it has failed. Manual intervention is not what the wife thinks is a good design, and as I am out of town 3 weeks at a time, I'm afraid she will call someone to do what I have already tried, and charge for it.
I'm ready to start easter-egging this, as it is the season!
Brian
[this message was edited by bmac56 on Fri 21 Mar 02:10] |
| | marchvac
| "Re(4):Goodman 100-4" , posted Fri 21 Mar 10:23
I would have to see a wiring diagram and I don't have access to one. If you still have the manual you could scan it and post it or if it is on the back try to take a picture of it. Normally on a high efficiency furnace the sequence is
Ventor motor comes on
air prove switch closes
module gets power
spark or glow
pilot flame proves
main gas. Be careful with some of those expensive air filers it might be too restrictive.
blower.
Be careful sometimes you don't get a second chance
|
| | bmac56
| "Re(5):Goodman 100-4" , posted Fri 21 Mar 16:19
The schematic is on the inside of the door, in KY. I am on the road now, so it will take a day or so to get it posted.
The blower pressure switch is in series with the rest of the interlocks to call for gas, but the blower motor is driven from the PVS. I cannot state with authority how it wires in, and senses the Tstat call for heat, so when I get the posting done, we can continue.
Thanks again, Brian
Brian
|
| | bmac56
| "Re(6):Goodman 100-4" , posted Wed 2 Apr 09:32:
Update: I ordered a Power Vent Sequencer, and the schematic that came with it shows it to have a time delay on/off characteristic. That is the answer to the original question in my posts here.
This is what I surmise the sequence of events to be in my furnace:
When the Tstat calls for heat, the PVS coil and the gas valve are energized. The gas valve is powered through the interlock series circuit, one contact being the pressure switch. It is made when the power vent motor starts, which is done at the first closing of the Tstat. The PVS will cycle the blower on and off the whole while according to its duty cycle, in my case, 1-25 sec on, and 65-115 sec off. The rest of the controls just take care of temperature limits being exceeded and driving the circulation fan when appropriate.
I will be sitting in front of the furnace again during a cold spell to verify this sequence. For now, the new PVS is installed, and all seems well. Of course, it may take three weeks for the intermittancy to show up again if this was not the fix.
I will post schematics and PVS diagrams at photobucket, at this link http://i246.photobucket.com/albums/gg89/bmac56HVAC
Brian
[this message was edited by bmac56 on Wed 2 Apr 09:51] |
|
|
