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 > Suburban Furnace No Delay

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pcdj64

Waterbury

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Posted: 11/07/19 04:48am Link  |  Quote  |  Print  |  Notify Moderator

I don't know if this is anything to be concerned about.
My Suburban furnace has no delay starting or stopping.
It blows hot air and can be adjusted with the thermostat but it always is immediate fan starting up and the whole thing immediately stops if you turn the thermostat down or off.
I got the RV used and there was never a delay with the furnace.

dougrainer

Carrolton, Texas

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Posted: 11/07/19 05:40am Link  |  Quote  |  Print  |  Notify Moderator

This is a safety hazard. ALL RV furnaces have a built in delay on starting(Purge Cycle) and a delay in stopping(cool down cycle). So, you have a unit with no functioning sail switch and a no functioning Hi limit switch. Somebody has modified your furnace. What year/Brand/Model is RV and what model Suburban. Doug

PS, on start up, some models the fan will come on immediately, but there is still a 15 to 20 second delay on burner. Does your burner come on immediately? If not, then your start up is OK.

Airdaile

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Posted: 11/07/19 06:15am Link  |  Quote  |  Print  |  Notify Moderator

There is a thermocouple that keeps the fan running after the burner shuts off. Post the model of Suburban furnace you have and someone here will have a part number for you.





rhagfo

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Posted: 11/07/19 06:29am Link  |  Quote  |  Print  |  Notify Moderator

Are you sure it is running on gas??
What you are describing is a furnace modified with the RV Comfort Systems "Cheap Heat" electric add on system.
When heating with electricity it starts up instantly once the T-Sat is changed. When heating on gas it will operate normally with the normal startup and shutdown delays.
RV Comfort Systems

Look for a switch either near the T-stat or by the furnace location that has two positions 'Gas" or "Elect". If found when in the elect position you are heating with electricity

[image]

* This post was edited 11/07/19 06:54am by rhagfo *


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dougrainer

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Posted: 11/07/19 08:01am Link  |  Quote  |  Print  |  Notify Moderator

Airdaile wrote:

There is a thermocouple that keeps the fan running after the burner shuts off. Post the model of Suburban furnace you have and someone here will have a part number for you.


It is not called a Thermocoupler. It is a Bimetal disc tstat. Doug

Old-Biscuit

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Posted: 11/07/19 08:41am Link  |  Quote  |  Print  |  Notify Moderator

Or it is your circuit board........

Many have the BLOWER Circuit ON the circuit board vs the OLD Time Delay Relay

YEAR & MODEL of the Furnace????


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pcdj64

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Posted: 11/07/19 09:47am Link  |  Quote  |  Print  |  Notify Moderator

I don't know model, 30,000 BTU suburban 1987.
On startup fan starts and a little time passes and then gas flows and ignition fires.
If i turn off thermostat it shuts down fast.
It is original 1987 old school non digital thermostat.
It has never been modified, i compared it to another identical furnace and everything is tbe same, there isn't a time delay relay but there is a large gold relay with a lot of wires.

dougrainer

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Posted: 11/07/19 10:03am Link  |  Quote  |  Print  |  Notify Moderator

You have the old NT series Suburban furnace. You have the Bi metal wall tstat from your description and from your last post it is functioning as designed. Doug

PS, the gold relay is the fan relay used on older model Suburban furnaces. It is called a tstat relay. It takes the low amp signal from the wall tstat and engages that relay. Going from memory, but your model has a fan switch on the burner case. It is at 145 or 150 degree switch.

* This post was edited 11/07/19 10:45am by dougrainer *

dougrainer

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Posted: 11/07/19 10:54am Link  |  Quote  |  Print  |  Notify Moderator

This is the operation for your model. Doug

SEQUENCE OF NORMAL OPERATION
(I)When the thermostat calls for heat, the blower
motor is energized immediately.
(2) As the blower motor reaches approximately
75 percent of the normal r .p .m. (within 3 to 5
seconds) the microswitch, in response to the air
flow, will engage allowing current flow to the
solenoid valve and the spark ignition system .
(3) The current to the valve opens it and allows.
gas to the main burner . The spark then ignites
the main burner .
(4) After main burner ignition, the flame detector
will sense the presence of flame (usually within
7 seconds) and deenergize the lockout feature .
If the main burner does not ignite or the flame
detector does not deenergize the lockout feature
within 7 seconds, the unit will go into lockout.
At this time, it will be necessary to set the
thermostat on OFF and repeat steps I through 6
of the lighting instructions .
(5) After 3 attempts with no ignition or main
burner continues to go off within 7 seconds, go
to shutdown and determine cause . (See service
hints)
(6) If within a period of approximately 2 minutes
after the main burner is lit, the thermostat is
turned back, both the blower motor and solenoid
valve are deenergized . However, if the furnace
continues to run longer than 2 minutes, which it
normally should, a slight snap can be heard from
within the casing . The snap is caused by the
fan switch as it changes its position . After this
occurs, if the thermostat is satisfied or turned
back, the solenoid valve will close, the flame on
the main burner will go out, but the blower will
continue to run for a short period of time and will
then shut off. The purpose of this is to remove
most of the remaining gases from the heat exchanger. Be assured that this period of blower
override is a part of the unit's normal operation

pcdj64

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Posted: 11/07/19 02:06pm Link  |  Quote  |  Print  |  Notify Moderator

Thank you for all of the replies and the details on it.
It does do exactly as you described, i only had to reset the thermostat once when there was still air in the lines from the propane being off.
the only thing it does not do is run for any length of time if you shut off the thermostat, it stops immediately.
I never let it run long enough to really get hot, i just got the RV and was pretty much testing everything. I had it on for maybe 7 minutes to make sure the air warmed up and there was hot exhaust outside.
I was off on the year, it is a 1984 not a 1987, my friend's furnace just like it is a 1987, i scavenged parts out of his because he is junking the RV and his furnace has a blown motor.
I timed everything on startup to make sure there was a delay after the fan starts up, i don't know a lot about these furnaces and don't want a fire from it.

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