Tweaking Whirlpool Automatic Dryness Control

tsteves5 · Apr 16, 2014

The "Automatic" cycles on my daily driver 1987 LE5800S have never worked to my liking. The clothes are always damp after the cycle has finished. This dryer uses the thermostat for automatic dryness control. For example the timer advances if the thermostat is open and the heater is off. The timer is stopped if the thermostat is closed and the heater is on.

I'm toying with modifying the dryer so the automatic cycles dry more thoroughly. I have a couple of ideas.

I am curious, has anybody here done anything like this before?

imperial70 · Apr 16, 2014

Are you sure it's the dryness control and not clogged ductwork (internal to the dryer and external to the dryer)? My dryness control started doing that and I found that would warn me that I've waited too long to clean things out.

tsteves5 · Apr 16, 2014

I periodically check the ductwork and clean out the dryer. It's always done it. Even when the house (and ducts) were brand new.

combo52 · Apr 17, 2014

WP Dryer With Time-Temperature Auto Dry

The first thing to check is when you put a large load in the dryer the timer should not start advancing till the heater cuts off and that should be 15-45 minutes minimum, if it starts advancing immediately with the heater on you have a bad timer. the 2nd thing to check is weather the heater is cycling on the operating thromostat or the heater box safety thromostat, if it is cycling on the safety the dryer will cut off before the clothing is dry. If this is happening try running the dryer with no vent system attached for a 1/2 dozen loads and see how the AD cycle works.

These auto dry systems on WP dryers give almost no problems and generate almost no complaints in the field, almost always when we get this complaint the dryer is cycling on the heater box safety because of a bad exhaust system or problem within the dryer itself resulting in poor airflow over the heating element.

I have never seen any reason to modify this system as there is a large range of dryness selections on the timer so that the dryer should always be able to dry any size load. Do keep in mind no auto dryness dryer is designed to dry all items in a load if you try to dry bath towels and sheets in the same load or if you try drying dress shirts with blue jeans, the dryer will shut off when the lighter items are dry.

kenmorebd · Apr 17, 2014

Thanks for this thread, I have started using an 87 Whirpool Dryer and was kind of stuned to see the timer move when the dryer is off. I normally preset the drying cycle on the dryer when loading the washer, it spooked me to see timer move with dryer off.

tomturbomatic · Apr 17, 2014

Are you saying that even with setting the timer toward the most dry settings, it is still shutting off before the load is dry? If it has been this way since the beginning, I wonder if the dryer has a bad operating thermostat or a bad hi limit thermostat that is maybe cycling at too low a temperature. If you have one of those quick read thermostats, you should put it in the exhaust air stream and see what the readings are for when the heat peaks and cycles off and how low it falls before it cycles back on and compare that with what is stamped onto the thermostat. If the thermostat is not resetting properly after it cycles the heat off, it could be letting the heat stay off too long which would let the timer motor run too long, too.

Do you ever use the time dry cycle? Does it take longer to completely dry the load than the automatic cycle takes to partially dry the same load? Auto dry cycles generally take a little longer to dry than if the timer is properly set for timed drying.

As weird as it sounds, it is possible that a 50 cycle timer motor could have been put in your dryer either at the factory or by someone servicing the dryer and that would mess up your drying results.

tomturbomatic · Apr 17, 2014

quick read thermometers, not thermostats.

tsteves5 · Apr 17, 2014

Combo52 - The timer will not advance for a while with a large load. I know the timer is not advancing until one of the thermostats turns off the heater. You bring up an interesting idea about the dryer cycling on the high limit thermostat. I will test it. For what it's worth, I did some time testing on the dryer a couple of years ago. Over a few combined auto dry loads, the dryer ran for a total of 9.25 hrs. The heater was on for 3.95 hrs during that time.

tsteves5 · Apr 17, 2014

Tomturbomatic - That is correct. With a full load of evenly-weighted clothes, it will take 2 automatic dry cycles to get the clothes dry even when set to the "dryest" setting on the timer.

Timed dry seems to get the job done quicker. I don't think I have a 50 Hz timer as the timed dry seems about right. 60 mins on the timer = 60 mins in reality.

I will check the exhaust temps. I have a little non-contact IR thermometer that I can use.

tsteves5 · Apr 17, 2014

Test Results

Empty dryer, highest heat setting, exhaust system connected. While initially warming up, the dryer hearter cycled once for a few seconds on the high limit thermostat. After that, all heater cycling was on the operating thermostat.

Disconnected the exhaust system and took some air temp readings. Operating thermostat opens at about 158 degrees F, and closes at about 131 degrees F. I do not see a temp rating on this thermostat anywhere. Does anyone know what should be expected of a good thermostat? This is one of those heated "infinite" setting thermostats.

tsteves5 · Apr 17, 2014

I also confirmed that the timer motor is 60 Hz.

combo52 · Apr 18, 2014

WP Dryer With Time-Temperature Auto Dry

Your exhaust temperatures are right within expected temperature range for a dryer like this. Have you tried running loads without and exhaust duct on the dryer yet?, it does sound like it is cycling on the high-limit heater box thromostat.

tomturbomatic · Apr 18, 2014

Toby, When the dryer is in auto dry, once the timer starts advancing, does it ever pause in its advance? The reason I ask is because if it is cycling on the high limit thermostat, that does not pause the timer. When Maytag offered some time-temp auto dry models in the HOH design, long exhaust runs would cause the high limit thermostat to cycle the heat, but not the dryer timer so they would complete the cycle with damp laundry. That is why your machine is suspected of cycling on the high limit thermostat. This is also why Hamilton dryers did not have an automatically resetting high limit thermostat. If it tripped, a service tech had to reset it and before doing so had to find the reason. Often it was because people were only cleaning the top of the lint catcher and not the lower portion. Some older dryers used a piece of solder that actually melted in an overheating situation and that disabled the dryer but good until the cause was found, but that was when dryers operated at much higher temperatures.

I guess you have checked for a bird's nest, dead animal or other obstruction at or just inside the vent opening. Have you taken apart the blower housing? Things can fall down inside the filter housing and partially block the airflow which could cause the hi limit to trip or something could crawl into the vent run and die there, although that is generally smelly pretty fast. Certain fabric softeners can cause a lot of lint to buildup on the blower blades, too. A quick test John showed me is to lift the lint filter lid and partially pull out the lint screen while the dryer is operating and feel if there is strong suction.

Another big question: Have you checked the lint screen to see if the screen is clogged with fabric softener? This can be a big problem if anyone has used fabric softener sheets in the dryer. The screens can get so clogged that water will not even go through them. They have to be washed with a strong cleaner like Knight's Spray 9, a mild brush and hot water to break that film. If you have partial clogging of the filter, that could be tripping the high limit thermostat.

DADoES · Apr 18, 2014

Just to say ... the LDE7800 (super capacity Supreme 80, 1976 vintage) dryer we had often cycled on the hi-limit thermostat for a while when a large/heavy load was run (the timer advanced for the brief periods when the element cut-out). It would settle down and cycle on the operating 'stat *after* the load progressed a ways toward dryness. I was working summers at the local Whirlpool dealer (where it was bought) at the time and brought it to their attention. We did a "service call" to investigate, no obvious problem was found. Ted fashioned a sheet metal plug to cover the hole at top of the element duct, to no effect on the machine's behavior.

tsteves5 · Apr 18, 2014

Tom - I don't think that is correct. The timer would pause and run even if the dryer was cycling exclusively on the high-limit thermostat. According to the wiring diagram, the operating thermostat and high limit thermostats are in series with each other. This means that the timer will pause because when both the operating high limit thermostats are closed and will advance if either the operating or high limit opens.

I do have a pretty long exhaust run, but I regularly inspect it and clean the dryer including the blower box. The dryer air flow is strong at the exhaust outlet and the suction at the lint filter is good. That's a good idea about the lint filter. I might try it.

Regardless, when I tested the dryer it only cycled once briefly on the high limit. All of the other cycling occured on the operating thermostat. Same as DADoES. So I'm not convinced this is a high limit issue.

DADoES · Apr 18, 2014

The exhaust on our aforementioned dryer was not excessive in length. The dryer was located perpendicular to an outside wall so the duct made one 90°F turn from the dryer and out the wall. I sometimes would clean the filter mid-way through when a large load of towels/cottons was running and causing the hi-limit cycling. As I said above, the dryer was disassembled, examined for bad seals, clogging, etc., and it still exhibited the behavior under some load conditions. Maybe we were overloading it but a washer load should be a dryer load and the machines were a matched pair.

mrb627 · Apr 18, 2014

Hmmm...

Certainly seems like an airflow problem to me.
I would start looking at the airflow path as well as infiltration possibilities.

Since the fan is a sucker, an air leaks are going to bypass your heater chamber. Maybe the felt seal has been compromised.

Malcolm

tsteves5 · Apr 18, 2014

I replaced the dryer felt seals and the door seal a couple of years ago. It made no difference.

tomturbomatic · Apr 18, 2014

And the rear rollers are in good shape, not allowing the drum to have a gap at the rear where air could be pulled in thus bypassing the heater box and causing it to trip out on the hi limit?

I still think you need to be there while it dries, or tries to, and watch the timer dial to see if it pauses when the heater is on. You might need an ohmmeter for this to verify when the heater is on. If the timer runs out of drying time while the load is still damp, the timer is running too much and if the dryer is not operating on the hi limit thermostat, something is wrong with the operating thermostat and it is not opening the circuit to the timer motor.

Good luck. I would send you extra patience, but I have none.

tsteves5 · Apr 18, 2014

Good idea on the rear rollers. I will check them. I also plan to compare the volume of airflow through the heater box versus the blower. That will let me know if I have any other major leaks.

I had a meter connected to each thermostat when I tested them last night. That's how I know which ones were opening and when. It did also appear that the timer motor was only running when the thermostat was open and the heater was off.

combo52 · Apr 18, 2014

WP Dryer With Time-Temperature Auto Dry

A WP dryer like this should NEVER be cycling on the safety thromostat, this is an unsafe condition.

You have one or more problems, Toms suggestion about possible clogging of the lint screen should be checked, but I suspect that the real culprit is the long exhaust system. You may also have slightly higher voltage than 240 volts which will also cause this type of problem especially with anything less than an ideal vent, you may also have a safety thromostat that is failing [ they often become too sensitive before they fail ] I would change it.

Often when we have run in situations where the vent is long, voltage high etc I have installed a smaller heating element to make the dryer operate properly, improve durability of the heating element and most of all improve safety.

mrb627 · Apr 18, 2014

Is this dryer...?

Have the TOP lint screen or inside the dryer door lint screen?

Malcolm

tsteves5 · Apr 18, 2014

John - I will check the voltage too. Just out of curiosity, do you know the part number for a smaller heating element?

tsteves5 · Apr 18, 2014

Malcolm - It's a top lint filter.

tsteves5 · Apr 19, 2014

More Testing

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I tore down the dryer and cleaned it again. It is now completely lint free, even the inside of the blower housing and the blower blades. I also scrubbed the lint filter. It didn’t seem too bad but now you can eat off of it. There was maybe a cup of lint throughout the entire dryer. Most was in the bottom of the blower box. I found a couple of small air leaks. The first was where the lint filter box connects to the bulkhead. The foam had deteriorated. I replaced with new foam. The second was between the drum and the left side of the bulk head. I think the bulk head might have been bent a little. I fixed this too. I verified that the vast majority of the exhaust air comes through the heater box.

My exhaust duct is about 15 feet long. It is accessible from my basement. I took down the entire duct and cleaned it again. It wasn’t too bad either. There was about a half cup of lint in the entire duct.

I did test the line voltage. It’s 250.9 VAC. This means that I am running the 5200 W heating element at 5436 W, which is 4.5% higher. 

I now realize the error of my ways. I previously tested dryer cycling while the dryer was empty. This time, I dried a full load of wet laundry. The dryer cycled on the high-limit thermostat for about 60 minutes and then finished the rest of the time on the operating thermostat. I measured the temp of the heater box directly above the thermostat. It appears that the high limit is opening up at about 200 degrees. I believe the rated temp for this is 250, so it appears that I might have a weak high limit thermostat.

tomturbomatic · Apr 19, 2014

Good investigative work

You also have very high line voltage. You probably could get by with the smaller heater. John can give you the part no. That and a new hi limit thermostat should have your auto dry working properly.

How many elbows do you have in the vent run, 2?

tsteves5 · Apr 19, 2014

Thanks for the help everyone.

There are 4 elbows in the exhaust run. 1 elbow is a 90, the others are 45-ish.

I might change out the operating thermostat too. I have some concerns about the thermostat heater that I still want to investigate.

tomturbomatic · Apr 19, 2014

The elbows are the problem. If you read the installation instructions, you will find that the air flow is too restricted. 15 feet of vent is a lot even with one elbow.

tsteves5 · Apr 19, 2014

Exhaust Booster?

There isn't anything that I can do to shorten or straighten that exhaust run. Maybe an exhaust booster would help if I can find one that will fit.

tomturbomatic · Apr 19, 2014

Reread Combo52's post about using a smaller heater in dryers with long vent runs. It is simpler than using a booster fan. Vent booster fans require a special additional lint filter in the pipe. For situations like yours, Whirlpool made a dryer with a special blower that boosted the exhaust without compromising the airflow through the dryer.

Tweaking Whirlpool Automatic Dryness Control

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