Payne +90 blower shuts off after 3 mins

[danz]

Hi all,
I discovered this forum while searching for repair information for my Payne Plus 90 gas furnace. this unit was installed in 1989 by the previous owner. I only bought the house in 2005 so I do not have any maintenance history. I had a maintenance call done in 2005 after i bought the house and the repairman cleaned the unit. 2 weeks later there was water dripping onto the electrostatic air cleaner below and i called them back. the condensate box had failed and it costs $225 o replace it.

Anyway, the furnace has been running fine since it got cold here(2 weeks +) and yesterday, i noticed that the thermostate was set at 65 but the temp in the house was 61 but the blower was not working but the furnace was running. I turned it off and let it sit for about 20 mins, then turned it back on and it ran as usual....furnace runs(ignites for awhile) and then the blower comes on...3-5 mins later, the blower shuts down but the temp has not reached the set temperatre and furnace is still running. I let it run for awhile thinking that maybe the blower will run again but it never came back on. So i turned it off again. I tried this several times throughout the day and this is what I it is doing.

Turn furnace on on programmable thermostat control.
Furnace clicks on and ignites( can hear the igniters)
A few mins later, blower comes on. there is warm air blowing out of registers.
3-5 mins later, blower turns off but furnace is still running.

The usual behavior of the furnace is that the furnace will turn on, ignites and when it warms up, the blowers come on and until the temperature in house has reached the set limit, the furnace +blower will shut off.

I cleaned the electrostatic air cleaner filters before I turned on the unit for the season. I looked outside at the intake and vent out pipe and it seems to be clear. Can't see down into pipe cause it's vented through side of house.

I called the HVAC company but they can only come out late next week. So I thought I would try to see if I can solve this myself. I am fairly competent with DIY stuff around the house but have no experience with HVAC.

What should I do to troubleshoot?

[HayZee518]

Look into your hot air plenum for a box about two inches wide, four inches long and about an inch and a half deep. It should be fastened to the air plenum. It has a cover which you can remove. This is the fan hi-lo limit. Inside is an aluminum disk which turns. On it is a slot with two pointers. these pointers are adjustable to give you fan on and off times and a proportional band that the fan operates within. The other side of the disk is a helical element which turns when it gets hot, moving the disk and opening/closing a set of contacts. Could be your band is set too narrow. Other thing is the thermostat has a heat anticipator inside - it is a variable resistance that "senses" approaching the set point and shuts down the burner. you can vary this for more or less on time of the burner.

[danz]

Look into your hot air plenum for a box about two inches wide, four inches long and about an inch and a half deep. It should be fastened to the air plenum. It has a cover which you can remove. This is the fan hi-lo limit. Inside is an aluminum disk which turns. On it is a slot with two pointers. these pointers are adjustable to give you fan on and off times and a proportional band that the fan operates within. The other side of the disk is a helical element which turns when it gets hot, moving the disk and opening/closing a set of contacts. Could be your band is set too narrow. Other thing is the thermostat has a heat anticipator inside - it is a variable resistance that "senses" approaching the set point and shuts down the burner. you can vary this for more or less on time of the burner.

But why would the limit suddenly change since the blower has been able to run until the set temperature? My guess would be that the blower motor is either seizing up and running past a hi temp safety temp. the reason why I say this is about a year ago, the blower started making a slight noise whenever it turned on. Sounded like a bearing noise but since it did not stop, I did not do anything. Now when the blower runs, I have not heard the sound anymore which leads me to think that maybe something has changed.

I did not have time to tear into the furnace yesterday but will do so this morning. I will check the hi-lo set points that you mentioned and also check the thermostat. I don't believe the burner shuts down because i can still hear the burners.

Seeing that my furnace is getting close to 20yrs, should i be looking into a new furnace?

[HayZee518]

The limit's helical element is in the air flow path. Moving air has moving dust in it which deposits itself on the duct walls and anything sticking out of the walls, i.e. the helical element. The noise coming from a bearing should have alerted you as something's wrong. bearings don't squeak unless they're dry. Now you let it run - I'm thinking that the bearings {and not all bearings are ball bearings} may have worn themselves oval shaped. An oillite bearing is made of sintered bronze so it is porous and transmits oil to the bearing surfaces. Ball bearings self destruct if they don't have oil or grease in them. If the bearing(s) have worn down that much the motor rotor may be hitting the stator winding iron which is gonna need a new motor. I suggest if it is the motor you conduct yearly maintenance checks.

[danz]

Look into your hot air plenum for a box about two inches wide, four inches long and about an inch and a half deep. It should be fastened to the air plenum. It has a cover which you can remove. This is the fan hi-lo limit. Inside is an aluminum disk which turns. On it is a slot with two pointers. these pointers are adjustable to give you fan on and off times and a proportional band that the fan operates within. The other side of the disk is a helical element which turns when it gets hot, moving the disk and opening/closing a set of contacts. Could be your band is set too narrow. Other thing is the thermostat has a heat anticipator inside - it is a variable resistance that "senses" approaching the set point and shuts down the burner. you can vary this for more or less on time of the burner.

So I just opened up the furnace(398AA) and ran it and this is what happens

1. when the furnace first starts up, the thing ignites and i see a blue flame through the sight glass.and looked at the burners through the small sight glass.
2. after while, the inducer motor comes on and the burners turn on.
3. Now, it seems that what's happening is that after running for about 3-5 mins(both blower and burners), the burners actually shut off cause i saw the flame go out. (not reach set temp yet)
4. After 30 secs to a min, the blower shuts down but the inducer motor is still running.

I listened more intently to the blower motor when it came on but I don't think its the bearing sound that i thought i heard. it's like a slight whine.

[HayZee518]

the inducer motor runs as a purge of the combustion chamber. if the chamber filled up with gas it could cause a loud "whump" noise when it starts. evidently it sounds to me like the plenum is getting too hot too soon and is kicking off. the flame should oscillate from on to off as you heed heat. there may be another burner control relay somewhere. can you get me a copy of the wiring diagram?

[danz]

the inducer motor runs as a purge of the combustion chamber. if the chamber filled up with gas it could cause a loud "whump" noise when it starts. evidently it sounds to me like the plenum is getting too hot too soon and is kicking off. the flame should oscillate from on to off as you heed heat. there may be another burner control relay somewhere. can you get me a copy of the wiring diagram?

I sent it to you via email. Appreciate your help.

[HayZee518]

I got your prints, now I'm trashing through it and trying to give you some insight what to check. Gimme a few minutes.

[HayZee518]

Blower motor shuts down

From what I can see on the print, a few variables need to be closed before the pilot flame ignites and
the main valve opens. Thermostat connections R & W need to be closed to start the sequence. LS1 & LS2 (if used)
need to be closed. The are the thermal limit switches. The door interlock needs to be closed as it feeds 120 volts
to the system. 1LK is the door interlock switch. The 1DR relay is a DC relay. The main gas valve has a
relay on it that forms a holding circuit for the induced draft motor. AFS is a sail switch in the air flow path.
When you operate the thermostat, it feeds 24 volts to the 1DR (draft relay) and closes it's set of contacts.
When you have adequate draft, the AFS transfers from EC2-2 to EC2-3 and opens the pilot valve. PS is the pilot flame
sensor, and it looks like a millivolt relay. On the print, on the main/pilot valve is a symbol that looks like
a backwards "D" - this indicates a pressure switch that closes on pressure in. So with the pilot valve open it closes
the pressure switch which is the holding circuit for the pilot gas valve. IC is the ignitor control pack. It operates
on a time delay.
24 volts one side (common) is fed to the HFR, 1DR, ICR, CFR coil, and terminal C. The other side of the 24 volts goes
through LS1 and LS2 to terminal R and terminal 5 of the EC1 furnace control board. From what the print tells me, terminal H has no function
as well as terminal GH. GH just bypasses the normally closed contacts on HFR. HFR is the heating blower relay and
is a user defined time delay relay. LOO is a lockout device. If you just touch a wire between R and G,
the CFR relay will close - the fan will swap from low speed to high speed because of normally open contacts
in the CFR relay - So, CFR controls your blower motor. Because of the way it's connected, I suspect something is amiss in your thermostat
or its connections. A contact in your thermostat is opening, shutting off the blower motor.
When the CFR operating coil opens it swaps the blower speed from HI to LOW -and the HFR relay operates the fan in slow speed.
Look to those two relays - CFR and HFR
Let me know where this gets you

[danz]

Burners shutting off prematurely, blower is normal.

From what I can see on the print, a few variables need to be closed before the pilot flame ignites and
the main valve opens. Thermostat connections R & W need to be closed to start the sequence. LS1 & LS2 (if used)
need to be closed. The are the thermal limit switches. The door interlock needs to be closed as it feeds 120 volts
to the system. 1LK is the door interlock switch. The 1DR relay is a DC relay. The main gas valve has a
relay on it that forms a holding circuit for the induced draft motor. AFS is a sail switch in the air flow path.
When you operate the thermostat, it feeds 24 volts to the 1DR (draft relay) and closes it's set of contacts.
When you have adequate draft, the AFS transfers from EC2-2 to EC2-3 and opens the pilot valve. PS is the pilot flame
sensor, and it looks like a millivolt relay. On the print, on the main/pilot valve is a symbol that looks like
a backwards "D" - this indicates a pressure switch that closes on pressure in. So with the pilot valve open it closes
the pressure switch which is the holding circuit for the pilot gas valve. IC is the ignitor control pack. It operates
on a time delay.
24 volts one side (common) is fed to the HFR, 1DR, ICR, CFR coil, and terminal C. The other side of the 24 volts goes
through LS1 and LS2 to terminal R and terminal 5 of the EC1 furnace control board. From what the print tells me, terminal H has no function
as well as terminal GH. GH just bypasses the normally closed contacts on HFR. HFR is the heating blower relay and
is a user defined time delay relay. LOO is a lockout device. If you just touch a wire between R and G,
the CFR relay will close - the fan will swap from low speed to high speed because of normally open contacts
in the CFR relay - So, CFR controls your blower motor. Because of the way it's connected, I suspect something is amiss in your thermostat
or its connections. A contact in your thermostat is opening, shutting off the blower motor.
When the CFR operating coil opens it swaps the blower speed from HI to LOW -and the HFR relay operates the fan in slow speed.
Look to those two relays - CFR and HFR
Let me know where this gets you

After I took off the panels and watched the whole thing cycle though, I don't think the blower is shutting down abnormaly. The blower usually continues on for a min or so after the burners shuts down in order to scrub all the heat from the heat exchanger.

What is really going on is the burners are shutting down prematurely. And I don't think it's the thermostat that is shutting it down cause there's no click sound from the thermostat. I did a search though some of the posts and seems like maybe I should be looking for a flame sensor, or hot surface ignitor or the burner control card. I took off the plate(with the viewglass) and I see something that is is between the gas nozzles and the heat exchanger. is this where the HSI and flame sensor is located?

I watched it a few more times (shut down and let it cool for awhile between each cycle). and each time, the burner is shutting off prematurely. The blower just follows the normal routine of shutting off a min after the burners shut off.

[HayZee518]

furnace

OK. I have the print in front of me. Let's do some troubleshooting using a meter.
Use a V-O-M with a voltage setting of 200. The furnace should be ON and not calling
for heat. The black lead we'll call the COMMON and the other the TEST lead.
Place the COMMON on L2.
Place the TEST lead on L1 - should read 120 volts.
Place the TEST lead on LINE-1 - Should also read 120 volts. This is the other side of the door interlock.
Place the TEST lead on EC1-4 and EC2-5. - Should read 120 volts. This one side of the DRAFT RELAY.
Place the TEST on PR-1 This is the transformer primary. (120 volts)
NOW

Remove the COMMON and place it on SEC-2
Leave the range switch on the meter on the 200 volt range. We will now be measuring 24 volts.

Place the TEST lead on SEC-1 - should read 24 volts
If you have LS2 you should read 24 volts on both sides of the switch.
If you have LS1 you should read 24 volts on both sides of LS1. One side of the switch
is called EC1-5 and is connected to R screw. It is also connected to one side of the HFR relay
contact which is normally closed with power OFF and comes out through the H screw.
24 volts also feeds to one side of the HFR relay coil, which energizes the relay coil.
GH should have 24 volts on it.

There is something called FL - this is an over temperature FUSIBLE LINK. It is part of the
PILOT valve HOLD circuit. Without this the PILOT valve will open and close, open and close

The PILOT ignitor is a high voltage spark gap. there is no HOT SURFACE ignitor in this unit.

PCB2 is the inducer control board. PCB1 is the furnace control board.

Looks like the flame detector is a FLAME-ROD. Looks like just a wire inserted into the PILOT
flame. Uses electronics to operate.

[danz]

OK. I have the print in front of me. Let's do some troubleshooting using a meter.
Use a V-O-M with a voltage setting of 200. The furnace should be ON and not calling
for heat. The black lead we'll call the COMMON and the other the TEST lead.
Place the COMMON on L2.
Place the TEST lead on L1 - should read 120 volts.
Place the TEST lead on LINE-1 - Should also read 120 volts. This is the other side of the door interlock.
Place the TEST lead on EC1-4 and EC2-5. - Should read 120 volts. This one side of the DRAFT RELAY.
Place the TEST on PR-1 This is the transformer primary. (120 volts)
NOW

Remove the COMMON and place it on SEC-2
Leave the range switch on the meter on the 200 volt range. We will now be measuring 24 volts.

Place the TEST lead on SEC-1 - should read 24 volts
If you have LS2 you should read 24 volts on both sides of the switch.
If you have LS1 you should read 24 volts on both sides of LS1. One side of the switch
is called EC1-5 and is connected to R screw. It is also connected to one side of the HFR relay
contact which is normally closed with power OFF and comes out through the H screw.
24 volts also feeds to one side of the HFR relay coil, which energizes the relay coil.
GH should have 24 volts on it.

There is something called FL - this is an over temperature FUSIBLE LINK. It is part of the
PILOT valve HOLD circuit. Without this the PILOT valve will open and close, open and close

The PILOT ignitor is a high voltage spark gap. there is no HOT SURFACE ignitor in this unit.

PCB2 is the inducer control board. PCB1 is the furnace control board.

Looks like the flame detector is a FLAME-ROD. Looks like just a wire inserted into the PILOT
flame. Uses electronics to operate.

Thanks for the steps. I came back too late today to look into this. Will try this tomorrow and report back.

[danz]

I got home pretty late every night this week and had some time on Wed night. I tested the points that you mentioned and they were all correct. Since it was already a week that I had the problem and the repairman was due to come on thu, i just left it as it. He came and pretty much did the same things that you mentioned.. and his deduction is that something in the gas valve is not right cause when the spark comes on, it's supposed to release gas for the pilot light but after it's warm(2nd cycle), it doesn't do that. He said that there's a control board in the gas valve and the 24V that's going in there, may be causing something to heat up. Since the gas valve is not a servicable item, the only thing is to replace the entire unit.
He's going to order one and come in sat to put it for me. Otherwise, he said that everything else is good, all voltages are triggering correctly.
Do you know the part number for the gas valve and how much it would cost? I'm sure he'll take his cut for the part +labor but with me having to work late pretty much everyday, there wasn't much i could do about it on the weekdays.

[HayZee518]

check out this site - there are a few gas valves. see what kind you got and compare it.
Gas Valves - Payne: American HVAC Parts