Kenmore Soft-Heat GAS dryers

[kenmore71]

Here's a question for the Kenmore experts out there:

 

Kenmore introduced the "Soft-Heat" concept in about 1963.  Initially on their gas models they used a continuously modulating gas valve that actually used a capillary tube and bulb that adjusted the output of the burner to maintain a steady temperature in the exhaust manifold.  I have seen one of these in action in Don's (Jet-Action) 1965 model 800.

 

In their later years did they continue this design or was it "cheapened" somehow?

 

The reason I ask is that I am about to bring home a 1970 model 70 gas dryer that bills itself as "Soft-Heat".  HOWEVER, this is an automatic dryness control dryer that is NOT electronic.  It appears to use a thermostat in the exhaust manifold like so many other mid-line dryers did until only recently!  I just don't see how a continuously modulating gas valve could be used on this type of dryness control.  Now in a week or two I'll be able to report how this dryer actually works, but until then I WANT TO KNOW

 

[tomturbomatic]

If this is anything like the control on the gas combo, as I remember it, when the flame tapers down to a point where the operating temperature cannot be held down even with the least amount of heat, the dryness control shuts off the gas and the timer advances to off. There is a weird thing about the gas system and how it is measuring the heat that John has explained a few times to me, but it always seems to boggle my mind so he will have to explain it to you.

My KA has both electronic and timed dry cycles and the original burner was replaced with the 37.5K BTU burner out of an old KM dryer with the perforated drum back. With the solid bulkhead drum back, the airflow is much more efficient. Generally within 5 to 8 minutes, at the very longest, even with heavy fabrics, the exhaust temperature has reached 165F and holds steady throughout the cycle. If I happen to set the timer for too much drying time, the flame goes out before the cycle ends because of the mondulating control so even the timed dry cycle is sort of an auto dry cycle because the heat shuts off when the load is dry.

You are right in wondering how a heat source that does not cycle can operate a time/temp auto dry cycle, but it does.

 

[arbilab]

There was nothing "soft" about my ~1990 Kenmore Soft Heat except the bezel text. I throttled the burner valve down so it wouldn't make sheets smell like they had been in a fire. There was no proportioning, the burner was strictly on or off. But it still said "soft heat".

Other than lying to me about "soft", the auto-dry module failing, and the main gas valve failing, that dryer ran for 17 years and was still running when I sold it with the house.

 

[coldspot66]

Current versions of "soft heat" means that the last few minutes of the heating cycle is controlled by the low heat thermo. The bias heater on the 4 wire thermo is in the circuit to shut the heat at the lower temperature, instead of the high heat temp.

 

[kenmore71]

Ah, that is good to know!  That's how they have gotten away continuing to use that moniker all of these years!

 

[combo52]

2nd Generation KM Soft Heat Gas Dryers

When the modulating input gas dryer burners disappeared around 1970 Sears continued to use the name SH on their dryers. I am not quite sure how they justified doing this but I think it was because the old system ran around 165F and the newer dryers just used a fixed 155F exhaust thermostat, maybe Gordon or someone else knows, but I am sure Sears had some justification for continuing to use the SH name to cover a cost cutting move.

 

Sometime in the 1990s the SH name on KM dryers and the Gentle Heat name on WP dryers referred to the fact on the auto-dry cycles the thermostat temperature setting did reduce as the timer moved toward the cool-down period of the drying cycle. This was done by the timer turning on a little heater in the control thromostat to cause it to trip sooner and therefor reduce the exhaust temperature.

 

 

 

[kenmoreguy64]

The moniker "Soft Heat"

I don't have a complete answer about the origin of Soft Heat or how it was conceived by Sears in later versions, but I do have some info that might help.

Having read and re-read Sears catalogs over and over again, both when they were new and recently, I know that Soft Heat was indeed a feature in 1963-ish models, through the 60s, and then it seemed to go away in the early 70s for quite some time, at least as a marketing term.

My mother's 1972 dryer was sold as an Auto Fabric Master model --- none of those dryers from that era had adjustable heat switches, at least most didn't and I don't recall Soft Heat, even on the TOLs. The catalogs say the dryers automatically adjust the heat as clothes dry, just as the old term "Soft Heat" would suggest. I do know that our dryer, which was gas, was much less warm late in the cycle vs. early on when things were really wet. It was still heating too, and not in the cool-down phase.

Though Soft Heat may have come back at points in the 70s, it made a huge comeback, and for quite a while, in 1983. Models with and without Soft Heat were carefully price pointed and marketed accordingly.

In 1986 when I bought my Kenmore pair, naturally I was quite focused on the washer, but because so many machines could interchange with the common panel styling, I had a choice of dryers. There were only two large capacity models on sale, thus that eliminated five or six other options. I bought the same basic dryer as Mom's 1982 dryer, less the adjustable cycle signal. No soft heat. I did not know it, but I got one of the better selling models.

There is/was a version of my dryer, which sold about as well, which DID have soft heat, and that was the only distinguishing feature between the two models. These are 70-series models. There was a standard capacity with and without group as well, they are 60-series units. I have not studied them closely in parts diagrams to see what is different, but I do know that in both cases the soft heat "equipped" models do use different timer part numbers vs. those that don't.

I have a copy of my dryer with Soft Heat now, so maybe one day I should compare the two side by side.

So, in a nutshell, 1980s models anyway use different timers than their counterparts without soft heat. For what its worth...

Gordon

 

[daveamkrayoguy]

Seems as if a lot of brands had their own "drying system" and a fancy name for it...!

Not to mention promising the "best performance" over its competition...!

Frigidaire boasted "Gentle Heat", while General Electric promised the fewest wrinkles, and don't forget Maytag's "Halo Of Heat", while similar systems & trade names were offered by Whirlpool, Norge, Westinghouse & so on...!

-- Dave

 

[vintagekitchen]

Soft heat too soft for me..

I never really cared for the whole soft heat idea. It was fine for loads of shirts or sheets, but it always seemed to me that the soft heat models left heavy loads like jeans or towels slightly damp, requiring starting the dryer over for a bit, where as the regular heat models left them dry at the end of the cycle.

 

[tomturbomatic]

Soft Heat has nothing to do with the degree of dryness. If anything, the original Soft Heat system should dry slightly faster because older dryers used to cycle the heat by heavy disc thermostats that had varying ranges of of temperature between heat off and heat back on while the Soft Heat system provided a constant drying temperature so the load was not subjected to the drops in temperature in the dryer during the time the heat cycled off and when it cycled back on. Placement of the cycling thermostat and its responsiveness determined how long the heat was off. Because of their mechanical nature, the thermostats had to cool 15 degrees or more before the heat cycled back on. That could lead to a greater drop in air temperature which would slow drying.

Newer dryers use faster acting, more responsive thermisters to cycle the heat, often cycling the heat off and on in a couple of minutes.

 

[vintagekitchen]

Shouldn't affect dryness

I can see your point, all I can do is speak from experience, and I promise, in the 2 soft heat models I have used, that was the case. Heavy loads slightly damp at the end. Since humidity is always so high in Kentucky that could be part of the problem, not sure.

 

[neptunebob]

Once I saw a Frigidaire "Wrinkles Away!" dryer was that like soft heat?

 

[tomturbomatic]

Frigidaire used the term "Flowing Heat" in their vented dryers in the 60s. Actually, I think the air-flow Filtrators were also said to have Flowing Heat. I guess it just meant that the heat was moved through the load by a fan. [this post was last edited: 7/4/2013-15:19]

 

[electronicontrl]

Soft Heat & Cushioned Heat

Hey VintageKitchen!,
I agree with you in regards to Soft heat and dryness level.
I have a 1992 KitchenAid dryer (which I truly enjoy) but I had to make accommodations for it. When I dry towels or other heavy items I select "very dry", otherwise I have damp clothes at the end of the cycle. Being a Maytag buff and selecting Maytag's "normal dryness" for loads which always came out dry, I was not thrilled with damp towels. But bumping up the dryness setting works just fine. (KitchenAid calls theirs "cushioned heat").

 

[DADoES]

 
I had the same experience with my 1991 KA dryer.  Jeans & towels had to be set at maximum dry to come out acceptable ... which they'd have to been recycled if I really did want them "more dry."  My current dryer, everything comes out fine on the so-called "normal dry" level.