Fan clutch solenoid

Fan clutch solenoid DEFAULT

Horton Fan Clutch Solenoid Valve - 993310

Product Description

When it comes to the efficiency of the fan clutch system, every component counts. The Horton solenoid valve helps provide accurate fan drive engagement from the vehicle system to the clutch. Without a properly functioning solenoid valve, damage can be caused to the rest of the engine cooling system and/or cause it to not work properly. This Horton fan clutch solenoid valve has a 3/64 in. orifice on the inlet and outlet for smooth engagements and disengagements. It is available in both 12 and 24 VDC, and its design and operation helps the fan clutch system improve available horsepower with less fuel consumption. With over 65 years of experience in the industry, Horton continues to be a trusted leader in fan clutch innovation and design.


  • Provides accurate fan drive engagement from the vehicle system to the clutch
  • 3/64 in. orifice on the inlet and outlet for smooth engagements and disengagements
  • Available in both 12 and 24 VDC
  • Design and operation helps fan clutch system improve available horsepower with less fuel consumption

More Information


Product NameHorton Fan Clutch Solenoid Valve - 993310
Lead Time30
Part StatusCurrent
Unit of Measure (case, ea, drum, etc.)each
UOM Quantity (Per Unit of Measure)1


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How this works

The Horton fan clutch has an important function in a truck’s operation, yet it is one of the most overlooked and least maintained components. In this feature, we’ll explain how the Horton fan clutch works, what maintenance it requires and importantly what to keep an eye on

A Horton fan clutch’s prime function is to engage and disengage the engine fan with a clutch controlled by an air-actuated solenoid valve. On modern vehicles, the solenoid receives signals to turn on and off from the engine’s ECU. On older trucks, the signals are sent from the temperature sensor.

The clutch engages and makes the fan turn when the valve opens, sending air pressure to overcome a spring and push the Piston Friction Disc (PFD) against the friction material. It disengages when the valve closes, allowing the clutch solenoid to exhaust air and let the spring return.

Most vehicles also have a manual override switch which will allow the driver to activate the fan on the approach to a hill to bring the engine temperature down. Conversely, on a long descent, a professional driver will manually activate the fan to help aid engine retardation because the fan soaks up 30 to 40 horsepower.

Horton Fan – What to look for

In the event of fan clutch slippage, heat builds up at the outer edge of the Piston Friction Disc (PFD). This heat works its way toward the center of the fan clutch. When damaging levels of heat reach the System Sentry the fuse will melt. This allows air pressure in the fan clutch to drop, disengaging the fan clutch immediately.

When the System Sentry has released the fan clutch, it has done this to protect your investment. This protective action also alerts you that there is a problem, so you can troubleshoot and repair the problem immediately. Catching problems in the early stages will keep damage and downtime to a minimum.

Fan Blades

Fan blades should be checked for correct clearance to the radiator, shroud and engine components. Check, locate and remove anything that may be an obstruction to the fan blade. Check that there are no cracks or splits in the fan blades that might cause the fan to run out of balance.

Clutch Slippage

A fan clutch needs 100 psi (6.8 bar) for solid engagement. Look for a problem that is causing partial engagement – usually, air leaking past the solenoid valve seals into the airline causing a pressure build-up. Is there a pressure drop causing partial disengagement? This usually is caused by an inoperative solenoid, airline blockage, up-stream air leaks, air leaks from the fan clutch body itself or low air pressure.

Routine inspection of the Horton Fan Clutch should be carried out at 200,000km intervals. Remove and plug airlines at the Fan Clutch input. Loosen fan belts, rotate the pulley and feel for smooth rotation of bearings. Repeat this procedure on the front section of the fan clutch. Check friction facing for wear, the friction facing should be approximately 4mm thick.

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High Temperature Solenoid / Fan Clutch Solenoid

Product Details

Special Notes
Product Description
Manufacturer: S & S Newstar
Part Number: S-16945
Condition: New
Fan solenoid valve kit
Replaces Navistar part number 1689-785-C91
Can be set up to run 'normally open' or 'normally closed'
Designed to operate at 125 to 150 psi
Includes wire harness and other accessories shown above

Cross References: 1689785C91, 993225, 993321, 08-03151
A cross reference listing means that this part may be a suitable replacement for the part numbers listed. Please check to be sure that this item matches your application.

Fan Clutch Solenoid Drawing

Normally Closed

  1. Port 'A' is left open as a vent or exhaust
  2. Port 'B' is the Supply port in the normally closed solenoid
  3. Port 'C' is the Outlet or Delivery port

Normally Open

  1. Port 'A' is the Supply port in the normally open solenoid
  2. Port 'B' is left open as a vent or exhaust
  3. Port 'C' is the Outlet or Delivery port
Fan clutch solenoid replacement on a kenworth t660

Selecting Proper Fan Drive Controls

Whether a vehicle’s fan drive electrical control is normally open or normally closed can be a confusing issue. It is also an important one, since the type of electrical control system indicates the field maintenance procedures necessary in retrofitting or replacing cooling system components.

Horton fan drives are air engaged (90 – 120 psi) and spring disengaged. They operate by an electrical control system and optional controls.

The basic electrical control system consists of a thermal switch and a 3-way solenoid valve with or without an air filter.

The simplest and surest method to determine whether a vehicle equipped with a Horton fan drive has a normally open or normally closed electrical control system is to inspect the solenoid valve. With a normally open electrical system you will have a normally closed solenoid valve. The normally closed solenoid valves are pictured in Diagrams A1 and A2.

With a normally closed electrical system, you will have a normally open solenoid valve. The normally open solenoid valves are pictured in Diagrams B1 and B2.

Thermal Switches

The thermal switch is an integrated engine temperature control and/or over-heat protective device.  Its switching circuit features mechanical load switching.  It is designed for frequent or high current switching.  Controls include the fan drive, radiator shutters and engine shutdown (overtemp).


Single pole, single throw.  Instant switching action (less than .001 seconds.)  No chatter.

  • Ambient Temperature Range:  -65 to +300 °F
  • Material:  Case and Terminals are brass.  The header is molded plastic and is high temperature resistant.
  • Current rating: 3.0 amps resistive, 3.0 amps inductive.
  • Electrical source: +12VDC to +24VDC
  • Life: 500,000 cycles at rated current.
  • Set Point: 175-230 °F in 5° intervals.
  • Set Point Accuracy: ± 2.5 °F
  • Switch Mode:  Normally open or normally closed.
  • Differential:  (reset point) Switch shall return to normal position 7 ± 2 °F below its point of operation.
Solenoid Valves

The solenoid valve controls the airflow, from the vehicle’s system, to the clutch for complete and accurate fan drive engagement.

The Horton air valves are a 3-way solenoid with a 3/64” orifice on the inlet and outlet for smooth engagements and disengagements.  The valve is available in both 12 and 24 VDC.

If the air inlet enters the side of the solenoid and exhaust air releases out the end, the electrical control system is normally open.  If the air inlet enters the solenoid from the top and exhaust air releases out the side, the electrical control system is normally closed.


If using a solenoid valve not supplied by Horton, use a 3-way normally open valve with a 3/64” inlet and outlet orifice.

If you fan drive is ECM controlled, it will use a normally open solenoid.

Air Conditioning Pressure Switch

The A/C pressure switch actuates the fan drive when the refrigerant pressure reaches the maximum switch setting.  It is normally open and is used with normally open electrical systems.


Clutch solenoid fan

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