Suburban heater cycles on & off

[dsbike]

I know this is an old thread, but there doesn't appear that anyone has come up with a diffinitive fix.

2001 Winnebago Journey 35' DP, Suburban SP-42 heater. This RV is my parents.

Our problems is as follows: When the heater is turned on at the thermostat the fan comes on for about 30 secs (normal) then the burner kicks on (normal) then after 3 min the burner kicks off but the fan continues to run to cool the heat chamber for about 90secs, then the burner kicks back on & continues to cycle like this until desired temp is reached. Not normal, when it was extremely cold this past winter it would not get the coach warm enough to ever turn off.

This is what we have done so far:
Last fall we replaced the high limit switch thinking it was turning off pwr at a low temp. No help. While the heater was out of the RV we cleaned the fan for the heater. Checked the floor plenum for any restrictions, none.

At this point it was Christmas week & did not have time for any more troubleshooting. Jan 1st my parents headed to central Fl. There they had an independant service tech come & work on it. He said the converter/inverter was bad & the heater was getting insufficient pwr. He replaced this & charged them 3X the price of the converter/inverter + $450 labor. No help, later had the old con/in checked out, operated properly. Yes he ripped them off, a story for another post. My dad replaced the propane gas regulator due to insufficient flow. They continued to use electric heater all winter until they returned to NC where we have been TSing this now.

Present: We contacted Suburban Factory Service Techs. They have been very helpful, but we still are not operating properly. Per the techs suggestions we have done the following. Measured the cold air return in side the RV, 35sqin, tech says it need to be at least 88sqin. We opened up the floor to allow more airflow, we now have 112sqin of air intake in to the heater & replaced the high limit switch again. The heater now runs for about 5min before cycling & has a bit more air coming out of the floor vents. We removed all floor registers & inspected the duct work for any restrictions, none. We ran the furnace with the registers removed, no change. We tried to measure the amp draw on the heater motor, but we did not get the desired measurement the tech told us we should, he wanted us to check the red wire, there are 3 red wires, tried them all, Could not call him back due to after closing hours, I will call tomorrow.

We removed the heater from the RV & bench tested it, the heater/burner ran continuously until we blocked off the hot air exhaust almost completely, to apprx 10sqin. At this point it finally cycled off & on. I also found a placard on the heater box that says the air intake needs to be a min of 142sqin. We closed off the air intake on the bench to simulate the present amount of opening we now have , it did not shut off the burner. I am leaning now towards adding another register or opening up one or more of the present registers to a larger size, but I don't want to cut up the floor unless I am sure this is the fix. We also checked that there is no register blowing on the t-stat to cause this to happen.

Sorry for the long post, but I wanted to avoid the replies that lead us to do what we have already done. I know several other people have had this problem, has anyone come up with a truely positive fix?

[DAN L]

i would try blowing through the heater ducts both ways with a leaf blower. mice may have built a nest in the duct where you cannot reach.
my sf 42 runs well with 3 of the 6 registers open.

[dsbike]

Duct works are clean. Opened up one of the registers to help facilitate hot air exhaust, no help. Although the air coming out of the registers is continously hot, the gas continues to cycle on & off. Latest check confirms that the burner stays lit for 2 min, then off about 30sec, repeatedly.

[Dave78Chief]

You have already covered the most issues that can create this problem.
The DSI control board monitors the flame via the elctrode(s). Some systems have 1 electrode that does both ignition and monitoring. Others have 2 electrodes. Make sure they are both clean and adjusted properly. The DSI control board itself could be defective also.

Dave

[DAN L]

Quote:

Originally Posted by dsbike Duct works are clean. Opened up one of the registers to help facilitate hot air exhaust, no help. Although the air coming out of the registers is continously hot, the gas continues to cycle on & off. Latest check confirms that the burner stays lit for 2 min, then off about 30sec, repeatedly.

here is some info that may help.

http://bryantrv.com/docs2/docs/SFseriesservice.pdf

Marksrv.com Suburban RV furnace parts

[TXiceman]

Please see the other post HERE

Thread is locked...Double post.

Ken