I have a Whirlpool NULK100DH01 gas furnace.

I want to increase the blower speed on my furnace. There is no wiring schematic and I haven't been able to find one online. On this one the colored wires that are for the different speeds all have a labeled place that they stay and there are other wires that look like the ones that would be moved to change the speed, one is purple and one is yellow. Is it the purple wire that is controlling the blower speed? Would I just move the purple one to the higher speed?

 

Not an HVAC guy but from what I thought all the furnaces come set with max speed of fan... It needs to be wired for low speed or multi stage out of the box...

Like I said I could be wrong... Wait for the pros....

 

Move the purple wire from the *red*( med-low) to the *blue* ( med).
Make sure to shut the power off to the furnace before doing so.

 

Thank you so much for your reply canuk.

 

You're welcome. Glad to help

 

^Check the temperature rise (supply temp-return temp close to furnace) BEFORE and AFTER you change the blower speed. Make sure it's within the range specified on the model number/data plate.

Too much or too little airflow can ruin your furnace.

 

For your interest:

Cooling and heating use different speeds, wired at the factory.

On a decent duct system I would think that the factory heating speed should be okay. (adjustment may or may not be needed)

Cooling is set to the maximum from the factory and has to be reduced if a smaller a/c (than what the furnace was designed for) is installed

 

Thanks Muggle,

Yeah turning the fan speed up was a last ditch effort using what little knowledge I have on HVAC to keep my furnace running until I can figure out what the heck is going on. So I guess I'll spill it and give the story of what's going on. I live in northern Minnesota and its about 15 below here right now. I just moved into this house and I know heat was working previously. What's going on is the unit is lighting, warming, blower comes on just fine and then it takes about 4-5 minutes before the until gets too hot and trips the high limit (dial type) blower stays on, unit cools and within two minutes its relighting itself. Seemed like airflow to me so I checked everything obvious all vents open, all return vents open, temp on the high limit is set to 200 degrees, I pulled apart the return ductwork in the basement to check for blockages, I inspected the blower and it was only slightly dusty, tried running one cycle without the filter to see if it was too restricting with same result, flames are ok I watched them through a full cycle and they are not "dancing" or any one of them looking like its having any problems. I finally decided that I needed to call someone out and had to call about 20 numbers before I could even find someone that would come here. The dude had to of been the most incompetent person I had ever met, he did a whole lot of nothing for an hour and then scratched his head said he would go home and do some research and call me back and of course that was the last I heard of him. I find it so ridiculous that this is so common, I have read through a lot of the posts on this site and it is story after story of repair guys coming out to the house and telling the homeowner nothing or something completely wrong and then the homeowner posts the story on here and you guys tear it to shreds. So anyway I gave in and called sears yesterday even though I know how crazy expensive its going to be because that's the only other company I can find to come to Nashwauk and their first available appointment was Dec, 27! So that's when I decided to turn the fan speed up one setting in hopes that it would be enough to keep the furnace running just long enough that I can get someone here, it didn't work anyway I think it added like 1-2 minutes of running time before the high limit trips. I know this is bad news and that something is wrong and that I should not be running the furnace waiting on a high limit switch to shut it down, believe me I am taking it seriously I am just trying to figure out what to do or what else I can look at myself.

 

There are three possibilities:

1. Weak limit tripping prematurely
2. Furnace now over-fired
3. Low airflow due to plugged evap coil if you have a/c or secondary if it's high efficiency

^You can rule all of these out but you'll have to call a pro if it's overfired or your a/c coil is plugged with dirt.

 

There is no ac and unit is not high efficiency. So how can I check and rule out the other options mentioned (weak limit and over-fired)?

 

You can confirm that it's not overfired by clocking the gas meter -> Clocking a Gas Meter - Home Energy Pros

After that, you can confirm that there isn't an airflow problem by measuring the temperature rise: Furnace Temperature Rise Test - YouTube

If the temp rise is within range (specified on the nameplate), you should verify that it's the high temp limit that's tripping. (Do you have a multi-meter?)

If it's out of range, try using fiberglass filters and open every vent. For a regular <90% eff furnace with no a/c, fiberglass is all you need.


Can you post a picture of the top portion of the furnace? (couldn't find a manual, need to know what kind of limit/controls it has. if the furnace is old, it might have a combo fan/limit switch)

 

Muggle thank you so much for taking this under your wing.

I reviewed your links on clocking the gas meter and measuring the temp rise and these are easily something that I can do myself (there is already a hole drilled in the ductwork that I am guessing was used to measure temp rise) I am going to start completing them right now.

I do not own a multi-meter but would be more than happy to buy one if need be.

Yeah I couldn't find the manual online either, posting some pics

Also while taking pics I noticed something that I didn't before and not sure how relevant it is or if it matters but there is a good amount of orange in all burner flames.


Unit getting ready to hit high limit

 

Not a pro in HVAC but the blower motors get weak on the fan inducers..Will it cause that???

Also I think cracked heat exchangers cause that too if its not anything Muggle pointed out....

 

Lawrosa

If I had a cracked heat exchanger wouldn't that cause rollout?

 

maybe go to med-o with the heating wire yellow that purple is for the cooling side during the summer.heating needs the slower air so it canheat up going over the heat X...

 

Hi sjk1015,

Your furnace is high efficiency since it vents with a plastic pipe, so it has a secondary heat exchanger which might be very dirty.

What you have is a combination fan/limit switch with three tabs - in order: blower off (set to 90F or so), blower on (usually set to 120 +/- 10F), and limit (factory set and shouldn't need adjustment)

The metal disk physically turns as the furnace warms up - once the blower comes on, it should stop moving after a couple a few minutes. When there isn't enough airflow (or maybe if the switch is weak, or the furnace is overfired), the metal disk continues to move until the limit shuts down the entire furnace or just the burners.

Turn on the furnace and carefully observe what happens.

->A change in the color or shape flames when the blower starts indicates a cracked heat exchanger. No change doesn't guaranty that it's safe.

If you have any safety concerns, call a pro to check the exhaust and indoor air for CO, inspect the heat exchanger, and check the gas pressure.

It's definitely 20+ years old -> they don't build 'em like that any more.

 

Were you able to look in the big end or just from the motor end of the cage?

My furnace was doing this and the blower looked fine from the motor end, shiny even. When I pulled the blower out I found something quite different.....







I now clean it every summer. I could only see in one end, yours may be different.

 

Awesome.....finally got another guy out here, he was here for about an hour, when he said he "got er working" I went down and checked it out while he was still here and he was right, furnace was running and limit switch dial was sitting right around the 150 degree mark, I thought oh this is great. I asked him what the problem was and he said there was an airflow problem and that it had probably been off since there is new flooring in my house that they had probably covered up a vent or something (before I lived here). Ok now I am starting to get worried while this guy is talking to me and of course he has his hand on the door at this point and clearly wants to leave in a hurry. I asked him if he was going to write me up a bill and he said "no don't worry they will mail you one". So as soon as he is out the door I run downstairs to check things out. The furnace was still running with the dial sitting at 150 which seems awesome until I see that he has taken off the vent cover on the ductwork right above the furnace under where the ductwork begins to branch out which leaves a giant open hole and of course hardly any air is being sent to the vents. Then I look at the blower wiring and see that he has set the blower to high speed. So yeah sure of course its not overheating anymore but he didn't fix a damn thing.

Anyway that's not even the worst of it. Now I am realizing that things are way more screwed up than before. The blower is not coming on at the right time anymore and I don't know what he messed up because it was working fine. Before he messed with it the blower came on RIGHT when the dial hit the fan on temp EVERYTIME. Now, thermostat calls for heat, inducer comes on then blower comes on either BEFORE the pilot starts trying to light or DURING the pilot lighting process (making the pilot have a hard time even lighting). This is long before the dial hits the fan on temp so I don't understand why this is happening. Also when the house gets to required temp the furnace shuts off and blower stays on for a few minutes longer then shuts off but a few minutes after that it oddly comes on for maybe less than a minute and shuts off again.

Please help.....What did this guy to screw up the signal to the blower?

 

Check for:

1. A jumper between terminals W and G where the t-stat wires connect

2. Fan/limit settings -> ON = 120f +/- 10, off=90f

A high efficiency furnace shouldn't be hitting 150F; the problem is probably on the return side. (think secondary heat exchanger)

3. T-stat fuel switch set to electric (if you can control fan from t-stat)

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The pilot shouldn't have any problems lighting with the blower running; if blower operation has any impact on the pilot, your heat exchanger is leaking or the furnace room is being pressurized or depressurized due to duct leakage.