Compressor Start Circuits (part 1)

Compressor starting circuits for household refrigerators vary depending on age and manufacturer. Almost all employ a relay and overload. Some use a starting capacitor as well. Regardless of the configuration, they all serve the same purpose…to start the compressor and get it up to its rated rpm and provide over-current protection. It may not be important to know exactly how the circuit operates as long as one knows that if the starting circuit is defective the compressor cannot start.

Compressors are hermetically sealed electric-motors that pump refrigerant vapor. Like any electric motor they draw more current when starting than when running at their rated speed. Thus compressor motors have two windings, a start winding and a run winding. At approximately 75% of the rated speed the start winding is taken out of the circuit (by the starting circuit relay) and the run winding keeps the compressor running. The windings are connected to the starting circuit by a three-pin connector on the side of the compressor. The most common configuration is illustrated below. Again, depending on the age and manufacturer this arrangement might not apply.

The first refrigerator repair I ever did was to a compressor starting circuit. Unfortunately by the time I discovered the defective seven dollar part my mother had already bought a new refrigerator. It did make me realize that a very inexpensive part can cause a refrigerator not to work. Over half the Haier refrigerators donated to Habitat for Humanity by a national appliance retailer had defective compressor starting circuits from the factory. Most of the rest were damaged in shipment or had defective evaporator fan motors.

Keep in mind that the power to the compressor starting circuit comes through the cold control and defrost timer (if the unit has automatic defrosting) so if these parts are defective there may not be power available to the compressor. That said…most evaporator fans are wired to run when the cold control makes and most condenser fans are wired in parallel with the compressor. Therefore if the fan in the freezer compartment is running and the condenser fan on a forced-air condenser is running the compressor should be running.

A Few Facts About Freon

Freon was developed in the early 20th century to replace toxic gases such as ammonia, chloromethane, and sulfur dioxide used in early refrigerators. Freon (a registered trademark of Dupont) entered our vocabulary as a generic term for refrigerant. A refrigerant is a compound that undergoes a phase change from a gas to a liquid and back in a closed system. The refrigerant absorbs heat during the liquid to gas state-change and gives up heat in the gas to liquid state-change. All refrigerants share this repeating cycle of evaporating (liquid to gas) and condensing (gas to liquid) to remove heat from inside your refrigerator (or house in the case of air conditioning).

From the 1930s until the 1990s R-12 was the refrigerant used in household refrigerators. Due to its ODP (ozone depletion potential) it was replaced with R-134a which contained no chlorine and has a ODP of zero. Unfortunately R-134a is not compatible with the oil used in all those R-12 systems that are still out there. One cannot squirt R-134a into a system designed for R-12 without bad things happening. R-12 went out of production in the mid-1990s. The price went from 89 dollars for a thirty-pound tank to over a 1000 dollars for a thirty-pound tank.

R-134a has its problems though. Its ODP may be zero, but its GWP (global warming potential) is 1300. European car makers have agreed to stop using R-134a in car air-conditioning in 2011 and are working on systems that use CO2 as a refrigerant. This places American car makers in a bit of a dilemma as well as the Chinese who have invested huge sums in plants to produce R-134a for all those plastic refrigerators they were planning to sell us. I see refrigerant wars looming (metaphorically speaking). It isn’t just your refrigerator and car either. R-22, the refrigerant used in residential air conditioners for decades goes out of production in 2009.

The main thing a home-owner needs to know about refrigerants is that FREON LEAKS OUT…IT DOES NOT WEAR OUT (dissolve, use itself up, disappear mysteriously). If a technicians says your refrigerator is low on Freon, he needs to find the leak and repair it before recharging the system.

The 1350 Dollar Switch

I think I promised this post a few months ago. You will probably never experience this problem, but it is always a possibility. The first day that I volunteered at my local Habitat Home Store, I noticed a Frigidaire side-by-side in the shop that looked new. It was plugged-in and running. I asked the person showing me around if there was a problem with it. He explained that it had been returned to an appliance retailer as defective and it had been donated to Habitat.

He added that the freezer worked but the fresh-food section wouldn’t get cold. It had been in the shop for a month and no one could figure out why it would freeze ice but spoil the milk. Then he mumbled the usual probably a freon problem diagnosis. I checked the temperatures of the freezer and fresh-food area and found that the freezer was at -5 degrees F and the fresh-food compartment was +50 degrees F. The cold control was set to max and the unit ran constantly.

With a -5 degree freezer and a working evaporator fan the question wasn’t why isn’t the fresh-food section cold (since cold air was being blown into the section), but rather where is the heat coming from? This new 1350 dollar refrigerator had been shipped with a defective door switch. The fifteen watt bulb inside the air-tight insulated box warmed the fresh food section nicely since it never went off.

The replacement switch cost a dollar and the unit was sold for 800 dollars the next day. 

Going Green Takes A Lot Of Green

“Hey fridgeman,got a question for you about converting a chest freezer to a refrigerator.this is quite common with the beer kegerator crowd,simply adding an external thermostat.

this is also being tried by off grid solar folks to make an energy effecient fridge.

so here’s what I did.

starting with a 7cu ft chest freezer I removed the metal skin,picked the evaporator coils out of the foam then added 3″ of foam around the sides,top and bottom.I then covered the sides with FRP and reinstalled the coils on the outside of the box. It actually looks pretty cool.

so did I create a more effecient fridge or did I just waste a bunch of time and money?thanks fridgeman.”

Mark

Thanks for the thought provoking comment, Mark. Looking around the Internet at the latest off-grid and green refrigerators, most combine smaller size with more insulation to reduce energy consumption. One manufacturer of off-grid refrigerators uses over 4 inches of polyurethane foam around a 7 cu ft chest-type box. The price is almost 300 dollars per cubic foot of storage. The unit uses a 12 volt direct-current compressor and R-134 and requires about 2000 dollars worth of collectors and batteries to power it. Thus the true cost is over 500 dollars per cubic foot of storage. Going green still takes a lot of green.

Did Mark create a more efficient fridge? Yes…although we don’t know at what cost. Cold air is heavier than warm air so by using a chest-type box one does not lose as much cold when the lid is raised. When a standard refrigerator is opened the cold air literally falls out onto the floor. The (black) external static condenser coils likely radiate heat better than the coils beneath the metal skin. The biggest energy saver in Mark’s creation was the added insulation.