Tip & How-To about Ruud Rheem Enclosed Fan Relay 42-25104-06 Za2900-1c-24a

How to wire a fan relay

A fan relay has 2 switches, a NC, normally closed switch
and a NO, normally open switch.
The relay has a coil that acts as an electromagnet and when energized with 24 volts from the thermostat will close the NO and open the NC switches.
The NO switch is the High speed , the NC switch goes to Low speed however as it is NC a temperature or time delay is what actually controls the low speed, low speed is the heat speed.
The NO switch in the fan relay goes directly to the High speed lead, this is the Cooling speed and the Fan On speed.
The 24 volt coil in the fan relay is wired to Green from the thermostat and Common 24 volt neutral leg.

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1 Answer

how do i check fuel pump and fuel pump relay

Hi Greg
Disconnect it's cable connector if possible.
Use a MultiMeter and a couple of jumper leads to +12v & ground.
Or the cheap tester below will help.

Sometimes this is better done on the bench where you can see whats going on.

Relays are just using a 12v low current electromagnet being used to close a set of internal switches (contacts) to supply 12v to the Fuel Pump. The Relay Contacts carry a higher current than th fine thin wiring used on vehicles these days.

The fuel pump can be tested & run without the relay to prove it is working. Use jumper wires to Battery.

The relay can also be actuated (tested) using jumper leads & a multimeter. When the internal coil is energised it simply pulls switch contacts closed. A Multimeter across the contacts pins will prove this.
Relay Pin Numbers
DIN 72552 defines contact numbers in relays for automotive use;
  • 85 = relay coil -
  • 86 = relay coil +
  • 87 = common contact
  • 87a = normally closed contact
  • 87b = normally open contact

Relay Wikipedia the free encyclopedia

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Dec 28, 2015 | 1992 Mitsubishi Mighty Max

1 Answer

samsung model smh7178std, shut the door and the fan and lights come on automatically, if i lift up on the door the fan shuts off but light stays on.

some switches are normally closed "short position" press switch "open" it will be labeled NC on the one side, "stands for normally closed" and others will be NO "stands for normally open" press switch "short" if there is no change in readings when you press switch it is defective.

Mar 28, 2012 | Samsung SMH7178STD Microwave Oven

2 Answers

How to wire contactor on Sears ac condenser style 36LC-000087CR

The contactor for the compressor and outdoor fan is activated by your thermostat when you call for cool. The small coil is an electromagnet that gets 24VAC when you call for cool at the t stat. The red wire in your T stat connects to the blue (or sometimes yellow wire) in the t stat completing the 24VAC circuit and closing the contactor. The line voltage is supplied to the poutdoor fan and compressor upon the contactor closing.

You can manually pushthe contactor close and the outdoor fan and compressor should start. Do this with your hand on the insulated portion of a screwdriver and take the tip of the screwdriver and push the contactor closed. The compressor and outdoor fan should start. That tells you that you have a thermostat to contactor coil issue if the t stat does not close the contactor when you call for cool.

Aug 03, 2011 | Heating & Cooling

1 Answer

how do i find out why my 1991 toyota pick-up fuel pump relay is getting hot?

A relay gets hot as a normal fuction of it's use. Inside is an electromagnet, This generates significant heat, which is normal. The testing of the switch involves: does it work, meaning close and open the current to the fuel pump, at the correct times. My guess is yours does, and you have felt the relay.

Stated another way: you cannot have an electromagnetic switch continually activated without generating heat. This heat should be okay. IF, on the other hand, you start eating relays, something else may be going on. But heat alone is expected.

May 11, 2011 | 1991 Toyota Pickup

1 Answer

My understanding of this unit's operation is this: The electromagnet is what holds the toast carrier down. When you push the bar down a mechanical switch is closed and that lets current go through the electromagnet holding the carrier down. If the circuit doesn't put current through the electromagnet's coil when the mechanism is pushed down then it will just pop back up. Also if there is something obstructing the electromagnet's iron faces then the magnet won't be able to hold the carrier down. Either situation will cause the problem, When the circuit wants to end the toasting, it interrupts the current going to the electromagnet (thermoelectric switch?) even though the mechanical switch is still closed. This causes the electromagnet to release the carrier so it pops up and doing so, opens the mechanical switch. There is a 12A, 125 VAC relay on the printed circuit board that switches the 120V to the outboard heating elements. Since this relay is driven by the pc board's circuitry, you can turn off the outboard elements by pushing a small button ("Bagel") of a momentary switch mounted on the pc board. On my unit the outboard elements are strong (toasts OK) but the inside heating elements have weakened (need more time to brown toast). I assume that mechanical switch is not making as good contact when closed as it once did. So it appears that the 12A relay is still doing a good job (driving the outboard elements) but the mechanical switch (driving the inboard elements) apparently does not have the low contact resistance it once had. The mechanical switch (has a large black plastic housing) may need to be replaced on my unit and (from what I've heard) on many other owner's units. Does anyone know if it is available?

Sorry we do not sell parts here nor do we hav3e anyway to look up parts for you since we have no books.

Feb 27, 2017 | KitchenAid KTT340 2-Slice Toaster

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