Learn how your appliance is supposed to operate so you can determine if it is malfunctioning.
The water temperature control provides the current to the water inlet valves which govern the flow of hot and/or cold water into the washer. Hot, cold or warm options are provided for both wash and rinse on many machines. Economy models will integrate at least the wash temperature into the wash cycle control. The wash water temperature must be warm enough to dissolve the detergent but not so hot that it shrinks the clothes or causes bright colors to fade. The rinse cycle's function is to get detergent out of your clothes so the water needs to be warm enough to dissolve all of the detergent and flush it out of the clothes.
The water temperature control is a simple rotary switch configured to offer the various combinations of hot, cold and warm for the wash and rinse functions. If warm is selected for the wash cycle, both the hot and cold water inlet mixing valve solenoids are energized when the fill function is enabled. If cold is selected, only the cold water inlet mixing valve solenoid is energized when the fill function is enabled by the timer.
The ratio of the volume of hot water versus cold water that the mixing valve puts out is coded into the color of the valve. A mixing valve that uses a higher ratio of hot to cold water would be desirable in the Northern states to get the output temperature up high enough to dissolve the detergent. I have seen red, beige and blue valves. I assume that with both valves on, the red one will put out the warmest water and the blue one will put out the coldest water for the same input temperatures. Does anyone out there know the ratios versus the colors?
Top of the line washers will often have an "automatic temperature control", also referred to as an ATC or ETC (electronic temperature control). Whirlpool calls their system "AccuWash". When cold, warm or hot temperatures are selected, the ATC circuit balances the incoming water to achieve a programmed temperature (cold: ~70° F, warm: 90-100° F and hot: whatever temperature the water heater can provide). A sensor measures the temperature of the incoming water and an electronic circuit reads that measurement and switches voltage to the hot or cold water solenoid of the water inlet valve to allow the proper mix needed to achieve the desired fill temperature. On "hot", incoming water temperature may be allowed to fill unadjusted. On a "warm" setting, the cold is cycled on and off while hot is allowed to flow freely. On "cold", hot water is mixed with the cold to achieve a 70 degree fill which is the minimum temperature needed to properly dissolve most laundry detergents. On some washer models plain cold water is used for the rinse, unadjusted by an ATC. On others, the rinse water temperature may also be controlled by the ATC. [Water temperature info was provided by Chris Herndon]
The cold water hose's sediment screen is prone to plugging up with scale and calcium deposits. On models without an ATC, select hot water only while the washer is filling and then switch over to cold only. Was there a significant difference in water flow rate? If so, you should turn the water off and clean the filter screens in the hose ends and at the water inlets to the washer. Some models have those screens built into the valve itself. In such a case, if they can not be cleaned adequately, the water valve may have to be replaced.
Why the cold water side mainly? Because sediment will often buildup in the hot water tank before it has a chance to migrate through the house plumbing to the sediment screens at the water valve on the machine. The cold water (along with any sediment) is able to flow directly to the valve. A problem in the cold water supply may first (or only) be noticed by slow or nonexistent water flow during the rinse period since cold is predominantly used at that point in the cycle.
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