Longer furnace cycle time

[wacnstac]

I'd like to make it so my furnace cycle times and the corresponding temperature drops/rises are larger. This would reduce the number of types my battery has to provide the current inrush to start the motor and make the whole system less annoying.

Can this be done?

[Ganglin]

Not sure you can adjust the current furnace. If you replace it with a lower BTU unit it will cycle longer. That's why they tell you not to increase the BTU's when buying a replacement furnace - it will cycle too short and be uncomfortable.

[wacnstac]

I was wondering if there might be an adjustment at the thermostat.

[HowieE]

I had the same problem with my heater. The blower during the start and cool down period was on longer than the heater. There is not an anticipater in the stats used in most trailers so normal adjustment is not that easy.

What I did is place a small piece of match book cover between the bimetalic elements of the stat to increase the gap. This caused the reaction time to increase and has worked well ever since.

I am writing this late in the evening so if further discription is needed post your question.

[wacnstac]

HowieE that's what I'm looking for some way to get larger hysteresis on the on time. I don't care if I get 5 degree temp swings I just can't stand the thing being on, off for 2 minutes and back on again.

[nickcrowhurst]

Wac, this is called the "switching differential" in my neck of the woods. If you have the original analogue thermostat you can remove the stat cover, and at top left is a slider on an arc. Moving the slider adjusts the switching differential. There may be a + and - to show which way to slide it. If you have a replacement digital thermostat, the maker's instructions will explain which buttons to press. BTW, changing to a digital thermostat makes a huge improvement in ability to accurately regulate comfort with the furnace and A/C.
Nick.

[nickcrowhurst]

If anyone is interested in converting analogue thermostatic furnace control to digital thermostatic control of both the furnace and A/C, details are at:
http://www.airforums.com/forums/f427...ace-14953.html?
Nick.

[TIMEMACHINE]

Originally Posted by nickcrowhurst

If you have a replacement digital thermostat, the maker's instructions will explain which buttons to press. BTW, changing to a digital thermostat makes a huge improvement in ability to accurately regulate comfort with the furnace and A/C.
Nick.

Nick,

Thanks a bunch...I have been trying to figure out how to keep the short cycles from killing the batteries during boondocking as well as decreasing the anoying on/off noises.

John

[HowieE]

Lets see if I can illistrate what I said last night.

In the picture you will see a vertical pointer coming straight up from the spring coil. If you look closely at your thermostate you will note that the pointer is one piece folded over and inside that is a very thin piece of darker contact metal. Normaly that thin piece would be floating between the folded over pointer. What I did was insert a small piece of match book cover, About 1/8 in square on the right hand side of the thin darker piece to force it closer to the left.

There is a small magnetic force between the pointer and the brass pointer to it's right. By forcing the contact farther to the left that seamed to delay the make and brake points of the thermostat increasing the burner time as a function of the overall run time of the heater.

I had mentioned that these thermostats did not have an anticipator, poor memory. They in fact do and you can see that I have removed it from the circuit by moving the needle all the way off the heater wire with it's pointer pointing to 7 oclock and fully on the contact.

[jcanavera]

Not all thermostats have anticipator adjustments. My 2001 Safari had long run times which led to it being too warm and too cool. The Atwood analog thermostat came in two models and the one chosen by Airstream had no adjustment.

I purchased a Hunter Just Rite thermostat which had a digital adjustment for the anticipator setting. As it ended up I didn't have to make a change since the thermostat had a tighter tolerance and didn't allow the 4 degree spread that the Atwood had.

The Duo-Therm thermostat on my Classic has a digital adjustment. I really didn't need to tweak that either. Bottom line if you have an analog unit, look at some of the low cost digitals out there. There's some good stuff that will give you what you want for about $20 or so.

Jack

[campadk]

I have the opposite problem.... my cycles are way too long.. so its cold, heater comes on... gets to hot... then shuts off for 15+ minutes (cold) before it comes on.

Not sure if it because I am in Canada, but for some reason they put the thermostat in the bathroom of all places! So if the door is closed... well you can imagine the thermostat in an enclosed room... not the main trailer living space... DUH!

From what I have seen, our trailer in the US has the thermostat besides the monitor above the stove in the 75th which is in the center of the living space (makes sense)... must be some stupid Canadian law howver, that says we have to live by the temperature in the bathroom! LOL

[wacnstac]

Originally Posted by nickcrowhurst

Wac, this is called the "switching differential" in my neck of the woods. If you have the original analogue thermostat you can remove the stat cover, and at top left is a slider on an arc. Moving the slider adjusts the switching differential. There may be a + and - to show which way to slide it. If you have a replacement digital thermostat, the maker's instructions will explain which buttons to press. BTW, changing to a digital thermostat makes a huge improvement in ability to accurately regulate comfort with the furnace and A/C.
Nick.

I have the original analogue stat. I've printed your post and hopefully this will do the job for me.

[nickcrowhurst]

Wac, the arc slider I mentioned is well shown on the right in HowieE's excellent photo, above. In mine it was to the left. I agree with Jack that a $20 digital replacement from Wal-Mart, where I bought mine, is an excellent investment.
Nick.

[jcanavera]

Originally Posted by campadk

Not sure if it because I am in Canada, but for some reason they put the thermostat in the bathroom of all places! So if the door is closed... well you can imagine the thermostat in an enclosed room... not the main trailer living space... DUH!

Location has been a problem with both of the Airstreams I have owned. On my Safari and now my Classic, Airstream has placed the thermostat on the wall that also is common with the refrigerator. The problem with that placement is that the thermostat wiring runs through a hole in that wall which for all intents opens into the refrigerator compartment.

To this you add the running of any vent fan. Ususally the bathroom. In the cold weather that vent fan running now pulls in cooler air from the compartment and the furnace cranks up to the point of being burning you out. Now in the summer with the A/C on it's the opposite, the hot air being pulled in causes the A/C to run to the point of freezing you out.

In both trailers I've had to caulk those holes but it's not 100% and running that vent fan (and there are times where this is absolutely necessary ) makes for some wide temperature swings.

Jack

[campadk]

Just following up on our thermostat issue.

Here is a close up...



So if I understand this correctly, the arc slider at '1' allows you to adjust the switching differential, which would
be the temperature range before the unit cycles on/off. Seems to me this can also be controlled by adjusting the
screw at '2'.

Can someone clearify the usage of these two controls? I'm essentially trying to shorten the on/off cycle so we don't'
suffer through too cold/too hot cycles.

Too bad this darn thing is in the bathroom of all places!

Thanks

[Excella CM]

Adjustment #2 is how you convert a precise device into an accurate one. It calibrates the temp arm to read correctly.

One thing to check when you have short cycle times is for obstruction of the ducting or intake or a slow fan. Any of these will casue the firebox to overheat and shut-off prematurely.

[wacnstac]

I'm glad I asked this question. I don't seem to have adjustment #1 on my thermometer, so can I use #2 which I do have?

[Excella CM]

I'm pretty sure you'll need a different thermostat.

[nickcrowhurst]

Originally Posted by campadk

can someone clearify the usage of these two controls

Ignore 2. As stated above, I suspect it just enables the dial to show a more accurate number for the ambient temperature. Switch the 12v power off (batteries, 110v supply and tow vehicle umbilical). [I confess I don't bother to turn off the 12volt supplies.] With a finger, slide 1 across to the other end of the arc and see how the switching differential changes in practice when you start up the furnace after reconnecting the 12v. Then adjust it back a little at a time until it achieves your desired comfort level. I suspect 1. puts a variable resistance in the circuit.
This is a crude device. Changing to a digital thermostat is a huge improvement for very little outlay in time and money.
Nick