Tweaking Whirlpool Automatic Dryness Control

[tsteves5]

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]

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]

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]

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]

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]

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]

quick read thermometers, not thermostats.

 

[tsteves5]

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]

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]

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]

I also confirmed that the timer motor is 60 Hz.

 

[combo52]

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]

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]

 
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]

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]

 
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]

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]

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

 

[tomturbomatic]

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.