How to Wire an A/C Unit Wiring an A/C unit involves installing a double-pole, 240-volt circuit breaker in the main service panel, running a 240-volt cable to the A/C's location, installing a safety-disconnect switch there, and then running weatherproof flex from the switch to the A/C's terminal box. This isn't an especially difficult project but it will involve applying for an electrical wiring permit from your the building department, working with the NEC (National Electrical Code,) and using some basic applied math. The most difficult part of this project will be routing the cable from the service panel to the safety-disconnect switch. This may involve fishing the cable through finished walls and floors/ceilings. Locate the nameplate on the A/C unit and note the specifications for the "Continuous Duty Full Load Current" and/or the "Branch Circuit Selection Current." Calculate the minimum required Ampacity (Ampacity refers to the maximum current that a conductor of a given size can carry safely) for the branch circuit conductors by multiplying the "Continuous Duty FLC (Full Load Current)" or the "Branch Circuit SC (Selection Current,)" whichever is greater by 1.25, per NEC Article 440.32.

Compare the computed value with the values given in NEC Table 310.16, column one. If the computed value falls between two listed values, select the wire size with the next higher rating.ac unit turns off every minute Calculate the minimum rating for the safety disconnect switch by multiplying the "Continuous Duty FLC" or the "Branch Circuit SC," whichever is greater by 1.15 per NEC Article 440.12(A)(1.)air filter ac direction If this minimum rating falls between two standard ratings, select the next higher rated switch.ac unit not working properly Calculate the minimum circuit breaker rating by multiplying the larger of the two current ratings by 1.25 per NEC Article 210.20(a). Compare this value with the values given in NEC Article 240.6.

If the computed value falls between two standard ratings, select the higher rated circuit breaker. Apply for your wiring permit. Don't start the wiring until the permit arrives. Wiring the A/C Unit Mount the safety disconnect switch next to the A/C unit. Route the type UF cable between the service panel and the safety-disconnect switch. Install a cable connector in one of the safety switch's bottom knockouts. Remove 12 inches of the cable's outer jacket and secure the cable in the connector by tightening the clamping screws. Route the red and black circuit conductors to the top of the switch, strip off ¾ inches of insulation, and attach them to the main switch lugs. Attach the white circuit neutral conductor and the green/bare-grounding conductors to the switches neutral and grounding bars, respectively. Install liquid tight connectors in the switch and the A/C terminal box and make up the flex. Secure the flex to the switch and attach the red and black conductors to the bottom lugs on the switch.

Attach the neutral conductor and the system-grounding conductor as you did above in step 8. Attach the flex to the terminal box and make up those connections by attaching the conductors to the appropriately marked terminals. Remove the cover to the service panel and install the double-pole breaker. Install a cable connector and the cable in the service panel. Connect the red and black circuit conductors to the circuit breaker terminals. Connect the neutral and ground conductors to the service panel's neutral and grounding bars. Only one wire per screw or your installation will fail inspection. Call the local government building department for inspection. EC&M Journal Sizing a circuit breaker. EC&M Journal Code Calculations Article 440 Air Conditioning and Refrigerating Equipment An air conditioning system uses the outside condensing unit to force liquid refrigerant through a metering valve, found in the inside unit's... Wiring an AC electric motor is not particularly difficult if the manufacturer's manual is available.

But if the manual cannot be found,... Air conditioner units come in many types such as a window mounted unit, a central air system or units that are called... How to Install a Split AC Unit; How to Wire an Outlet Split Switch; How to Size Wire for a Central Air Conditioner. An air conditioning unit typically has two separate labels. Air conditioning units, while fully protected on the outside by a plastic or metal casing, are a complex web of wires and... Check the wiring once again to make sure all the connections are ... The run capacitor on an air conditioning unit is... Wiring an electrical alternating current (AC) switch involves some planning and forethought, but is not a difficult procedure. Safety needs to be... Air conditioning condensing units communicate with the furnace via two thermostat wires. The two wires are encased in insulation to make one... It takes no special skills to install a new breaker into your home's main electrical panel.

Circuit breakers are not interchangeable or... How to Install an Air Conditioner. Install the mounting brackets that came with the air conditioner unit (be sure to follow... HVAC condenser units allow people to be comfortable in their homes. Using refrigerant, they pull the heat and humidity out of the... How to Install 220V AC Disconnect Switch How Do I Install the Disconnect Box for an Air Conditioning Unit? How to Connect Wiring to an AC Compressor How to Repair a Thermostat Wire Connecting to an Air Conditioner Unit How to Wire from a Main Breaker to a Sub-Panel How to Install an Electric Disconnect SwitchRevised by BoatUS editors in April 2012Image courtesy of West MarineAir conditioning for boats has come a long way in recent years. In earlier days there were typically large compressor and condenser units in one section of the boat, (frequently the engine room), with air handlers and the evaporator in cabinetry within the living areas.  Freon or other “coolant” was transported to the evaporator via copper tubing covered with insulation.

(Freon is no longer used because of environmental concerns and there are several products now being used. For the sake of discussion and brevity we’ll use the term “coolant.”)This type of air conditioning is still used, principally in larger yachts, but developing technology has led to the option of buying a self contained unit that’s small enough to install within a cabinet in a living area. On larger boats, one or more self contained units are sometimes installed. There are various benefits to self contained units, including the fact that it’s usually easier and more convenient to install by the knowledgeable “do it yourselfer” and professionals, one doesn’t have the long run of coolant and, depending on the unit, it may consume less overall space and typically the unit will cost less.  Also many of these are essentially plug and play when it comes to replacing some of the parts and other service issues.  Following manufacturer instructions as to all details is critical.

Here are a few general considerations that may be helpful as you consider this type of air conditioning.Before you buy a unit, pay close attention to what the manufacturer of the unit you’re considering has to say. You’ll need to know the cubic feet that you want to cool, and measure it according to the manufacturer’s recommendations. For example, your cabin from bulkhead to bulkhead and/or side to side and overhead to deck is a certain number of cubic feet.  But if this space contains large cabinets or other structures the interior of which aren’t going to be air conditioned, your actual cubic footage may be considerably less. You’ll need to buy a unit that the manufacturer says is adequate for the space you wish to cool, using the method of measurement and calculation recommended by the manufacturer.  Usually you will find manufacturers and dealers quite helpful with this.  Don’t try to save money and undersize the unit.  You may end up finding that you’ve wasted the money you spent. 

Also, don’t try to grossly oversize the unit. This can not only waste money initially but also result in less than ideal performance. Do remember that your boat probably won’t be as well insulated from the outside as is your house.You’ll need to take the following into consideration as you decide the best location for your circumstances. You’ll need a cabinet or other space to contain the unit. If you don’t have one you may need to do (or have done) some carpentry. The unit should be in a dry, easily-accessible and ventilated location and not in the bilge, engine room, or near combustible vapor source. The space should be in a location favored by the installation instructions. For example, you wouldn’t want to place it where only your feet are cooled. Remember, that cold air settles, hot air rises.  Wiring will be important. It must be of recommended gauge. Probably you’ll have to install a wire run for the project. This may play a role in where you can mount the unit.Also plumbing for the raw water cooling will play a role.

These units are not cooled by air, resulting in a quite significant hot air discharge, as is your home unit.  They have a heat exchanger (coil) where water from overboard takes the heat from the coolant. Therefore there must be a pump located at some point in the boat, pumping water from a thru-hull, through a hose, to the unit. (In many instances one pump can service more than one air conditioning unit.) There must also be a discharge thru-hull well above the water line at maximum heel. All fittings must be double hose clamped, and the hose should be routed slightly upward from the intake through-hull through the strainer and to the inlet side of the pump and then to the unit.  Loops in the hose can result in air locks.  The intake thru-hull must be low enough so that the pump won’t be sucking air if the boat heels (as with a sailboat) or planes. All fittings must be double hose clamped with quality clamps and the thru-hull valve should be certified for marine use and properly installed according to ABYC standards which should be followed throughout.

There will be one more small hose run. The unit will produce condensate water on the fins. This is normally drained from a tray under the fins, either overboard or into a sump. Overboard discharge of this cold fresh water is preferable to diminish the development of mold and smell, but overboard discharge can lead to other complications, particularly in the plumbing run. This small condensate hose (more like a tube) should be run in a manner so that there are no kinks and you should be able to easily clean debris (such as accumulated dust) from its top end. Otherwise, over time this will clog the tube causing condensate water to run into your cabinetry and elsewhere.  (Many will clear this, if it occurs, simply by blowing on one end of the hose.)The cold air discharge ducts should be as short as possible. On some installations the air discharge is self contained at the unit avoiding the necessity of ducts. Also, the control containing the thermostat should not be in direct sunlight or other location which will inadequately reflect the cooling needs of the cabin space.