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Old 09-07-2003, 12:58 AM   #1
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Cary , North Carolina
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Winterize now!

Hello All!
Being September 8th I have decided to get a jump start on winterizing my '80 Excella II here in central NC. The first thing I have on my list is the Furnace since for the past 3 winters (I am full-time in my beloved silver palace) I have had the literal "hot head-cold feet" condition. After removing the Suburban NT-30 gas furnace from the unit I discovered through looking into the combustion chamber exhaust tube that the wasps and daubers love living in my A/S as much as i do! (no surprise there!). These small gas furnaces are somewhat of an enigma to me but fortunatley the P/O kept all manuals for the appliances etc...I am an Automobile mechanic and, more importantly, the manual for the furnace is Very well written , I now have a good "mental picture" if this little unit in operation. Please forgive me if i get too basic or too complicated in this post for i am sure this will be read by both "novices" (like me) and the more , shall we say, "adept" in the workings of our beloved silver Condos on wheels.
When I bought this unit (1980 Excella II rear bath, center twins-WBCCI 14992) the owner told me "no the furnace does not work". After getting the unit home and installing a new battery i moved the t-stat to call for heat and got-----nothing. Looking into the manual i saw that i should at least be getting fan-on. Took my fluke 12B multimeter to the t-stat wires and saw there was voltage going to- but no voltage from- the t-stat. Removed cover from t-stat and discovered a small section of a match book cover had been placed between the contacts.
Removed the paper and got fan-on but it seemed to be turning slow. I did not bother with the furnace again for 3 years since I have a heat strip in the overhead AC unit, Olympian 6100 Catalytic heater and i dont live a very cold climate. This year however I have decided to get the furnace going and am trying to figure out this slow fan speed problem. For those of you who do not know, the fan speed must reach a certain rpm before power to the "ICU"(ignition control unit) is activated. I have not taken the furnace apart yet so i believe the slow speed could be that it is packed full of wasp/ dauber nests but i have other reasons in mind also which i wish to relate.........With no loads (all 12v draws off) I have exactly 12 volts at the furnace with battery charger on. Every automotive electrical system i have seen has 14V or a tad better with the motor running (with no loads). If i turn on most of the other 12V loads in the unit , the Voltage drops to 11V. Possible weak Univolt? Anyway here is the good part: I took the 2 ECU's i have (found one in a drawer) to my local RV dealer to have them checked and was told they both are operational (amazing, they both look quite old).
So whats the deal on this slow fan?
Weak Univolt?
Low amps to fan motor? (wiring or????)
Bad fan Motor?
Constipated fan (impacted with critter nests)?
any other Ideas????

Id like to take the time to post the "sequence of normal operation for "Suburban Dynatrail Furnaces models NT-24M, 24MD, 30M, 30MD" (Dated 5-78) for my fellow 'streamers reading this who may not have the manual but THE FOLLOWING TEXT IS FOR INFORMATIONAL PURPOSES ONLY!! PLEASE HAVE YOUR FURNACE CHECKED AND REPAIRED BY A QUALIFIED R/V REPAIR TECHNICIAN!!!
(1) When the thermostat calls for heat, the blower is energized immediately.
(2) As the blower motor reaches approximately 75% of the normal R.P.M., the microswitch, in response to air flow, will engage, allowing current flow to ICU board.
(3) After a 12-18 second delay, current will pass thru the ICU to the solenoid (gas) valve.
(4) the current to the valve opens it and allows gas to the main burner. the spark at the electrode then ignites the main burner.
(5) After main burner ignition (usually within 18-25 seconds), the flame detector will sense the presence of main burner flame and de-energize the lockout feature within the ICU. After a 12-18 second delay, if the main burner does not ignite or the flame detector does not de-energize the lockout feature within another 7 seconds, the unit will go into lockout mode. At this time, it is necessary to set the t-stat to "off" and repeat steps 1-6.
(6) After 3 attempts with no ignition, or main burner continues to go off within 30 seconds, go to shutdown and determine cause.
(7) If within a period of @ 2 minutes after the main burner is lit, if the t-stat is turned back, both the blower motor and gas valve are de-energized. However if the furnace continues to run longer than 2 minutes, which it normally should, a slight snap can be heard from within the furnace casing. The snap is cause by the fan switch changing its position. After this occurs, if the t-stat is satisfied or turned back, the gas 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 gasses from the heat exchanger. Be assured that this period of blower override is a part of normal operation.

Again please have your furnace checked by a certified R/V technician as this post is for informational pruposes only!!

Just stumbled across this site, its a MUST READ for new full timers!

In closing id like to get back to the main purpose of this post which is:
So whats the deal on this slow fan?
Weak Univolt?
Low amps to fan motor? (wiring or????)
Bad fan Motor?
Constipated fan (impacted with critter nests)
any other Ideas????
Wishing all the best to all my fellow 'streamers!

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Old 09-07-2003, 08:08 AM   #2
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1959 24' Tradewind
Phoenix , Arizona
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Jason - I would venture a guess and say that the fan motor shaft probably needs a good cleaning and oiling. Our beloved beauties that are exposed to everything outside get dirty and dusty. The fans funnel all this grit right through them. Both of the fans on mine needed a good cleaning and the RPMs have practically doubled. Choose a suitable thin oil.


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Old 09-07-2003, 10:11 AM   #3
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1969 31' Sovereign
Broken Arrow , Oklahoma
Join Date: Jan 2003
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Mine is a bit older (1971) and had many of the same problems.

Final fix on the fan motor was take it out and have it rewound. I could not find an exact replacment, Mine has two sqirrel cages one on each side of the motor with a single shaft. Matching the shaft was the problem. Cost to be rewound was about the same as a replacment motor with the one side shaft.
I did luck out with the micro sw. Had an exact replacment in my junk parts just had to move the sail over.
I guess you know how important it is to seal the unit if you remove it or completatly take it apart as I had to do. The wick type sealer is available but can't remember where I got it. I think from a fully stocked TT dealer. Not sure but the orignal seemed to be asbestos. I also installed a wire guard at the exaust so the dobbers couldn't redo the damage.
Low voltage could be at the univolt fuse (correded). My low voltage was due to a wire that had been cut in the past and not reconnected using wire nuts just twisted and taped.
Over time I guess the wire just shook loose.

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