All posts by mike

After being in the HVAC business since 1975 we started Shortys HVAC Supplies in 2005 thinking there was a need for do it yourself parts. We provide factory authorized parts to make your repairs as simple as possible without a need to modify generic parts to make them fit.

Contactor Replacement

The easiest way to replace a contactor for a do it yourself repair is to first make absolutely certain the power is turned off. Also make sure the air handler is shut off as the 24 volts to the contactor is powered from there. If the 24 volt circuit is left powered on you stand the chance of shorting out a control wire and burning out the 24 volt transformer. After you have verified all power is off remove the mounting screws and pull the old contactor out of the way without removing any wires if possible. If you must remove wiring make sure and mark the location the wire was connected to. Install the new contactor. Disconnect each wire and reconnect to the new contactor before removing the next wire.  If you change one wire at a time you should not have any problems.

I have included a picture showing an old style contactor and a new style contactor. The new style has a dust cover over the contacts that is removable to inspect the contacts. The new style also has the 24 volt connections located on each side. The old style contactor does not have a dust cover over the contacts and the 24 volt connections are on the same side. I have drawn a red line beside the 24 volt connects for reference. The 24 volt connections are not polarity sensitive as the voltage is AC. It does not matter which connection the wires are placed on as long as both wires are not on the same connection.


Contactors can be purchased for do it yourself repairs from Shortys HVAC Supplies. If you are not sure of the correct part number please call or email us at and we will be happy to identify the correct part for you.

HVAC Split System

A split system is designed with  separate outdoor unit for cooling and an indoor unit for heating. The indoor unit can be a gas furnace with an evaporator coil, an oil furnace with an evaporator coil or an air handler with built in evaporator coil and electric heating elements. The indoor unit usually supplies the airflow for the heating system and the cooling system.

The outdoor unit is called the condensing unit. It is connected to the evaporator coil by 2 copper lines. The small line supplies high pressure liquid refrigerant to the evaporator coil. The large line returns the low pressure refrigerant vapor back to the condensing unit. This line will be below ambient temperature and should be insulated.

Since the indoor unit is used for heating and cooling the air filter is used for both modes. Keeping the air filter clean is critical to the proper operation of the system.

HVAC Package Unit

A package unit is a self contained piece of equipment designed for roof mount or sidewall installation. The equipment contains the complete heating and cooling system and comes ready to connect the ductwork. Package units are configured with openings in the bottom panel and a side panel for connecting ductwork. The unit is delivered with covers installed in place over the duct connections and the correct set of covers will be removed for installation depending on if the unit is to be ducted through a curb or sidewall.

When mounted on a flat roof it is very common to install the unit on a roof curb. The curb is mounted to the roof and flashed to make it weather tight. The roofing and decking in the center of the curb are removed to gain access to the interior of the building. The curb is constructed to be the same size as the unit so the unit will sit squarely on top of  it. Cross pieces are installed at the top of the curb to match the duct connections on the bottom panel of the unit. The ductwork is fabricated to drop in from the top of the curb with a 1″ lip folded out to rest on the cross pieces. The top of the curb is thin covered with a 1″ foam strip acting as a gasket to seal in the air flow. The unit is then set in place on the curb and ready for field connections for electric, stat, and gas if used.

When used as a sidewall installation the unit will be installed on a pad or some type of stand. The ductwork will connect to a sidewall on the unit and a return and supply duct will be installed from the unit through a sidewall in the building to connect to the building duct system.


Contactors are electromechanical switches that turn on the air conditioner compressor or electric heating elements. The critical ratings for a contactor are number of poles, coil voltage and contact amps. The coil voltage and contact amp ratings are typically marked on the tag of the contactor. The number of poles are actually the number of contacts or switches in the contactor.

In the picture below the contactor on the left is a single pole. It is manufactured using the same housing as the contactor on the right which is a double pole. You can see the contactor on the left has 1 set of contact points. The points on the left have been replaced in the housing with a bar that connects the top and bottom connections together.  The contactor on the right has 2 distinct sets of contact points so it is considered a double pole.

The amp ratings for a contactor are given as FLA for a motor load and RES for an electric heat load. The RES ratings is usually somewhat higher.

The coil voltage is rated for the voltage of the control circuit which is generally 24 VAC with most air conditioning systems.  I have added 2 red lines in the picture for the contactor on the left showing the 24 VAC connections for the contactor. As you can see the contacts are clearly separated from the main power contacts. The operation of the contactor is 24 VAC is applied to the coil via a common wire from the transformer. The other side of the coil is powered by the R side of the circuit through the thermostat. This energizes the coil and the magnetic field of the coil pulls in the contacts so they touch to start power flowing for the load. Power wires will be connected to the 2 terminals on top of the contactor and the compressor wires will be connected to the 2 terminals on the bottom of the contactor. When the contacts touch the compressor should start. Note the power wires and compressor wires can be installed on the top or bottom of the contactor.  As long as they are wired properly the system should operate.


Maintaining Your Air Conditioner For Cooling Season

Springtime is a good time of the year to do preventative maintenance on your air conditioning system. Taking care of small problems before it gets too warm may keep the equipment operating trouble free during the hot weather.

While you are performing these checks make sure the power has been disconnected.

Remove the cover over the unit electrical compartment and take a look at the wiring for any overheated or loose connections. All connections should be tight and the wiring should show no signs of discoloration. If the wiring is discolored that section of wiring should be replaced. Examine the contactor points looking for discoloration or pitting. Discoloration can indicate a bad connection when the points are energized. Also take a look at the capacitor for any signs of oil leakage. If the capacitor top is dome shaped or there is any sign of oil the capacitor should be replaced.

Check the condenser fan motor and make sure the blade turns freely. Also check the shaft for any side to side movement. If there is any side to side play in the motor the blade will turn free but the motor has worn bearings and does need to be replaced. The shaft will move in and out but it should not move side to side. Also look closely ate the fan blade. The individual blades are installed with rivets. The blades are usually aluminum and can stress crack around the rivets. If the blade is not changed it can tear and get caught in the coil. This can cause a tear in the copper tube and a loss of charge. If the blade does crack and break it will lead to a very expensive repair.

If you see any signs of an oil leak around any of the copper lines it indicates a refrigerant leak and we recommend getting this checked by a technician.

While you are looking at the motor is a good time to take a garden hose and wash out the outdoor coil. We do not recommend using chemicals to clean the coil as it can cause deterioration of the aluminum fins. Water should be sufficient for cleaning. Allow the unit to dry out for a few hours before restoring power.

Maintaining Your Air Handler For Cooling Season

Springtime is a good time of the year to do preventative maintenance on your air conditioning system. Taking care of small problems before it gets too warm may keep the equipment operating trouble free during the hot weather.

While you are performing these checks make sure the power has been disconnected.

The first order of business is to check the air filter and change if needed. This simple item can prevent the coil from  freezing up due to a lack of airflow. If your furnace or air handler uses a 1″ standard air filter we recommend using a good quality pleated air filter. We do not recommend using a 1″ filter with a merv rating higher than 8 as this type of filter may cause airflow restrictions and this can lead to inefficient system operation and in some cases cause damage to the equipment.  If you have a high efficiency filter cabinet we strongly recommend installing the correct air filter for the cabinet. This style filter is usually marketed in a nominal size. The filters do not all have the same outside  dimensions and a generic filter or an incorrect filter may lead to leakage around the filter which prevents all of the air from being filtered.

While looking at the air filter is a good time to make sure the condensate drain for the coil is clean and free. This simple step may prevent water damage if the drain is partially restricted or clogged.

While you are checking the indoor unit make sure the blower spins free and take a look at the circuit board for any hot spots or loose connections. Also examine the copper piping for any signs of oil or rubbing marks. Copper is a soft metal and rubbing on other copper lines or the sheet metal cabinet may cause a refrigerant leak. If you see signs of oil you may already have a leak that will need to be addressed by a technician.

Condenser Fan Motors

Condenser fan motor replacement is another easy do it yourself repair. Bearing failures are usually the reason the fan motor needs changed.

Always replace the capacitor when changing the motor. The capacitor is usually a dual type that services the motor and the compressor. When bearings start to fail the motor windings heat up. This heat is also generated in the capacitor and can cause damage to the capacitor. A damaged capacitor can cause failure of the new motor or the compressor which will be a very expensive repair. Capacitors are not expensive items and sometimes saving a small amount of money will lead to spending a large amount of money.

Before attempting any repairs make sure the power is shut off. Verify with an electrical meter. Mark the location where the wires terminate paying close attention to wire color. If you have ordered the new motor from Shortys HVAC Supplies the wiring will be exactly the same in most cases. Remove the wiring after marking and remove the cover with the fan motor attached. Turn it upside down and spray the shaft with penetrating oil. Do not tap on the shaft with a hammer or punch. Remove the locking screw in the collar of the fan blade. If there is any rust on the shaft beyond the fan blade sand this down to shiny metal so the blade will pull off easily. Reach between the blade and motor with pliers and hold the shaft. Gently twist the fan blade from side to side to get it to spin on the motor shaft. As it starts to spin gently pull the blade away from the motor. In most cases it will come off with no damage if you are patient. If not you can order a new blade as well. After the blade is off turn the assembly back over and remove the three or four locknuts holding the motor to the shroud.

Reassemble in the reverse order. We recommend greasing the motor shaft before installing the new blade to make it easier for removal if the motor fails again. Be sure and tighten the fan hub locking screw on the flat spot of the motor shaft. This flat spot is specifically machined on the shaft for this reason. If you tighten the screw down on the round part of the shaft it may slip. It will also be very difficult to remove later.


The most common use of transformers in furnace and air conditioner equipment is to step down the voltage to 24 VAC for the control circuit. Transformers have 3 ratings. Primary voltage which is the line voltage applied to the transformer primary winding, secondary voltage which is the 24 VAC control voltage induced in the secondary winding and the VA rating. The VA rating is the amount of power the transformer can supply without burning up the windings. VA stands for Volts X Amps which is the same formula for wattage. Many transformers are rated at 40 VA which means they are capable of sustain a load condition up to 1.6 A on the 24 V side.

Transformers have no moving parts. The only failure you should see with a transformer is caused by an overload condition such as a shorted wire or shorted control on the 24 VAC circuit causing an excessive amp draw. Sometimes a voltage spike such as a lightning strike will damage a transformer but it usually causes other damage.

Common failures are a bare spot on the wire caused by rubbing where it passes through an equipment sidewall, rodent damage in a crawl space or wall and wiring getting cut while trimming grass around the outdoor unit.

In the picture below you can see 2 different types of wiring for a transformer and how it is marked. The transformer on the right shows the 208 or 230 V connections on one side. The other side is marked load. The tag is marked PRI 208/230V SEC 24V  40VA. The transformer  on the left has the connections marked on the tag. The tag reads PRI 120V BLK-WHT  SEC 24V RED-BLUE 40VA. This designation means the primary is rated for 120VAC and connects using the black and white wire. The secondary is 24 VAC and connects using the red and blue wire.


Use for Start Assist Devices

Start devices are used to assist the starting of the compressor.  The conditions where start assistance is typically needed are when the compressor is old and worn or the system must start against a higher pressure on the discharge side. Older refrigeration systems used a fixed metering device like an orifice or capillary tube to separate the high pressure side of the system from the low pressure side. The flow rate through the device depended on the difference in pressure. When the system shut off the pressure would equalize somewhat rapidly through the fixed device. The next time the compressor started the high pressure and low pressure would be the same and the compressor would start with no assistance. As system efficiency increased more systems have been equipped with a self regulating metering device called a Thermostatic Expansion Valve or TXV. This device is a self adjusting metering device that will close off when the system shuts off. High pressure and low pressure will take much longer to equalize with this type of metering device so their is a good chance the compressor will cycle back on with a differential between the high pressure and low pressure. This causes a need for increased torque to start the compressor motor. This additional torque is generated by adding some type of starting components to the system.

Common start assist devices are a start capacitor with start relay, start capacitor with some type of thermal shut off and start thermistors. The start capacitor and start relay as well as the thermistor style must be matched to the application. The style with the thermal shut off are generic replacements that are typically used as a quick fix.

Carrier Nomenclature

Carrier Corporation has several brands that use the same part numbering system. The brands are Carrier, Bryant, Payne, Day & Night, Resco, BDP. The parts used in this line of equipment are identified by the product number located on the unit nameplate. Sometimes there will also be a series number on the nameplate. All of these numbers and letters are used for parts identification. If you look at the picture of the nameplate below you will see a serial number, product number and a model number. Nameplate If you look at the model number and product number you will notice they are very similar. The model number is PA13NR024-H. Carrier made several versions of this model and designated any change in parts used during the manufacture of the equipment with the product number. The product number is PA13NR024000AHAA. The additional letters in the product number designate changes during the manufacturing process. With this number we can see the exact part required for your application. You can contact Shortys HVAC Supplies at with the information from your equipment nameplate and we will be happy to identify the factory replacement part for your repair.