Testing Dryer Thermostats

how does one test dryer thermostats to see when they are opening at the correct temperature? I know that the continuity of them is fine; I've tested that with an ohmmeter, but suspect that one (don't know which is which)is not opening to shut off element. This is in a VERY old Frigidaire (GM product) dryer (1957), but I suspect the principle is the same now.

: how does one test dryer thermostats to see when
: they are opening at the correct temperature?
: I know that the continuity of them is fine;
: I've tested that with an ohmmeter, but
: suspect that one (don't know which is
: which)is not opening to shut off element.
: This is in a VERY old Frigidaire (GM
: product) dryer (1957), but I suspect the
: principle is the same now.

Technicians do not usually test a dryer's thermostat (thermodisc) for operation at the specific temperature. If it does not open at all or is always open, it is an indication of a component failure. If it does open at some time, it is assumed to be OK. It would be fairly unusual for a dryer's thermostat to continue to operate but only at a different temperature than it is designed for.

Testing the exhaust air will usually tell if a thermostat is cycling properly or not. On a low heat setting a temperature of 115°F-125°F would usually be expected, on medium 130°F-140°F and on high 145°F-155°F ... depending on the actual design of the dryer in question.

Dryers also often use separate thermostats for each of the different heat cycles. When the appliance is malfunctioning on a particular heat setting, it is often that heat setting's thermostat that is defective only, none of the others. Eg. If the dryer is not operating correctly on the low heat setting only, it's the low heat setting's thermostat that's causing the problem, not the high or medium's heat thermostat.

If the dryer is operating incorrectly on different heat settings, the problem is often elsewhere and not in one of the thermostats. If the dryer is not performing properly on all or many of the heat settings, a likely cause is plugged or improperly installed vent.

Dan O.

OK... so how does one tell which thermostat is for which setting?

This old dryer only has single element with 3 thermostats. I think I know which one is the overheat(closest to the element I assume). The other 2 are mounted in the air plenum (suction side)

: OK....so how does one tell which thermostat is
: for which setting?
: This old dryer only has single element with 3
: thermostats. I think I know which one is the
: overheat (closest to the element I assume).
: The other 2 are mounted in the air plenum
: (suction side)

The thermostats located on the internal ducting are the cycling thermostats and are the ones that cycle the heater on and off to maintain specific temperatures. Each will have a temperature rating marked on on them (see the following link), the higher the temperature, the higher the heat setting they are for.

LINK > Appliance411 : Repair Parts Showcase : Dryer Thermostats & Safeties

The one mounted closest to the heater is usually the safety thermostat. A safety thermostat should never operate unless there is a problem elsewhere in the dryer like poor air flow possibly caused by plugged or bad ducting, a defective blower or bad drum seals.

If it is the safety thermostat closest to the heater that is opening, you should probably be looking elsewhere for the cause rather than the thermostat itself.

Dan O.

Thanks... I will check 'em out. My father also had a dryer that was acting like this one, although it was much newer. I have checked the ducts of both and they are clean as a whistle (well, all most).
Jim

: I have checked the ducts of both and they are clean
: as a whistle (well, all most).

If it is an electric dryer, you can be certain if the venting is the problem by running the dryer with the vent completely removed. If it works OK then, you know the vent is (at least part of) the problem.

If it still acts up, check for air flow problems inside the appliance (bad blower, plugged lint filter, worn drum seals, etc.).

JMO

Dan O.
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