Wrong voltage being supplied at the field coil: Take an amp draw of the electrical system to make sure you have the proper voltage that is needed for the field coil. Correct coil resistance is 3-5 ohms.
Air gap between the compressor face plate and pulley is wrong: Check with OEM manufacture specs use a feller gauge and add or remove a face plate shim.
Bearing failure: Wore out pulley bearing, Check for pulley play or listen for noises around the compressor clutch area.
Compressor drive belt is the wrong type, width or miss-aligned.
Lock compressor: Due to excessive high head pressure- Make sure the system is not over charged with Freon or oil.
RECIRCULATION AIR FILTER
Recirculation air filter will be found inside the operators cab it will be located at the evaporator box it is very important to keep this filter very clean. Most of these filters are made of open cell foam, though some of the new filters are made of paper. Most foam and paper filters can be blown out with 20 to 30 pounds of air pressure. Most foam filters can be washed out with water. Failure to service will cause the evaporator coil to plug up with dirt, mud, debris causing poor or no cooling.
FRESH AIR FILTER
Fresh air filter will be found outside the operators cab it allows clean, fresh air to enter the cab area. Most of these filters are made of paper and filter particles down to about 19 microns. They must be removed and clean daily if the machine is operated more than 10 hours a day. Remember that if your equipment has the capabilities of bringing fresh in to the cab it also brings in the ambient temperature as well.
DRAIN PAN AND DRAIN LINES
The drain pan collects water from the evaporator coil and channels it out of the cab. If the pan leaks or drain lines become plugged with mud, the water that has condensed off the evaporator coil will enter the cab area. They will need to be flushed with water or compressed air. Check the drain lines for kinks, holes, sharp bends, flat runs or uphill runs.
THE REFRIGERANT OIL
The internal components of an air conditioning system must be properly lubricated with the correct refrigerant oil. There are several types on the market to day; PAG, Ester and mineral make sure you chose the right one for the type of refrigerant that is in the system. The oil is absorbed into the refrigerant that carries it though the compressor as a mist. An oil charge that is over or under can damage the compressor. Compatibility of refrigerant oil is determined by its ability to remain oil when mixed with the refrigerant and not become separated by a chemical reaction. R-12 refrigerant uses a mineral oil 5GS made for that refrigerant and can not be used in R134a systems. An R134a system uses either PAG oil or Ester oil. Note the following: PAG oils absorb moisture 100 times greater than mineral oil (in effect 1% water within 15 hours). Ester oil will mix to 50% with all PAG oil types.
Refrigerant leaks can cost lots of down time and money if not found and repaired. A good halogen leak detector will pick up leaks under static conditions; however some will leak only when the system is in operation. There are other ways of finding a refrigerant leak use visual inspection look around the refrigerant fittings & hoses for spots of refrigerant oil and dirt. Check the front clutch plate of the compressor for oil and dirt. If the air condition system is completely empty you may want to use dry nitrogen to pump up the system to hear a leak. Also they have a florescent dye that can be use to detect a leak. Note, to see the dye stain you need a UV lamp and the leak has to be where the light can reach it.
HOSES & FITTINGS
Refrigerant hoses carry the refrigerant from one component to the next. The hose should be of the barrier type (Twin Eagle Distributing recommends the Goodyear Galaxy hose) for R134a refrigerants and the beadlock style fittings. Most air conditioning systems use the #6 (5/16” ID), #8 (13/32” ID) and #10 (1/2” ID) refrigerant hose. Hoses need to be inspected occasionally for blistering, bulges, dry rot, chaffing, swelling and hardening. Check around hose fittings for traces of oil and dirt that may indicate a refrigerant leak. Keep hoses away from hot spots, moving parts, sharp edges, and oil leaks and watch hose routings on machines that articulate.
LOW AIR FLOW
The complaint: “it use to blow harder”, Things to check are:
Obstruction at the air return, plug or dirty filter
Debris in the evaporator coil that blocks air circulation
Icing of the evaporator coil due to bad thermostat switch
Air leak or obstruction in air duct hose
Defective blower relay
Blower wheel loose on motor shaft
Blower wheel rotation wrong
Blower motor shaft rotation wrong
Low blower motor voltage due to poor ground
Using a 24volt motor on a 12volt system
MUST I RECOVER (HFC-134a) REFRIGERANT?
YES! Most defiantly EPA has issued regulations under Section 609 of the Clean Air Act establishing standards and requirements regarding the servicing of motor vehicle air conditioners (MVAC).
Technicians who repair or service “Motor Vehicle Air Conditioners” must recover the refrigerant and either recycle it on-site, or send it off-site to a reclamation facility so that it may be purified according to ARI Standard 700. Technicians must use EPA-approved equipment to perform the refrigerant recovery and recycling. Technicians who service MVAC or MVAC-like appliances (“Farm & Heavy Equipment”) must be properly trained and certified by an EPA-approved technician certification program set forth in section 82.34, and the description of the specific requirements for approved training and testing set forth in section 82.40.
CHARGING A/C SYSTEM
After you have followed the rules set by EPA rule 609 and made your repair you will need a refrigerant manifold set. Attach the low and high side manifold couplings to the service ports on the A/C system. Attach the middle hose to a good 2 stage vacuum pump turn it on and open both the low and high side manifold wheels. Check the low side gauge to make sure you are going into a vacuum which is achieved when the needle goes below -0. You want to be close to 29.9 inches of vacuum let it run for at least 30 to 45 minutes. Note: that at higher altitudes you will not achieve -29.9 inches of vacuum. If you are above 3,000 feet let the vacuum pump run at least 15 minutes longer. After you have achieved a good vacuum close both high and low side manifold wheels check the low side gauge and note where the needle is. After at least 5 minutes recheck the needle if you are loosing vacuum that will indicate a leak in the A/C system (Repair and Start Evacuation Again). When ready to charge remove the center hose from the vacuum pump and attach it to the refrigerant keg, make sure you purge the center hose at the manifold gauge to let any trapped air out. (Just Crack Open and Close) Charge with vapor only not liquid. Next open the low side manifold wheel you will notice that the high side gauge needle will start to move up away from 0 after the low and high side needle are equalize or close to it, you are now ready to charge. Start the engine and turn the fan speed on high and a/c switch on. Check with the a/c manufactures for how much refrigerant the system requires. If you can’t obtain that information see the section on charging an a/c system using a pressure temperature chart.
CHARGING AN A/C SYSTEM USING PRESSURE TEMPATURE CHART
After following the steps in the section CHARGING AN A/C SYSTEM You will need to take the fresh air intake at the condenser make sure you are reading the cool air coming in not the warm air leaving the condenser. Add 35-40 degrees (F) to the temperature you took at the condenser for example lets use R-134a and the temperature reading was 90 degrees (F) you add 40 degrees (F) that, gives you 130 degrees (F). Look at a R-134a Temperature Pressure Chart find 130 degrees (F) you will find that = 200 PSIG when your high side gauge reads 200 PSI, close the low side manifold wheel that will stop the refrigerant flow entering the system. Take your louver temperature then check the high side gauge if its below 200 PSI add a little more refrigerant to the system till it reaches 200 PSI. Be careful not to over charge the system, check your louver temperature if it rises with the compressor on then that could indicate over charging.
Bubble Circular Crimp
An Orifice tube is a fixed metering device located inside the liquid line between the condenser and evaporator. The orifice tube is enclosed with a plastic housing and protected by a fine mesh filter. The filter helps prevent debris from entering the system. Orifice tubes are usually color coded. An accumulator only or accumulator & drier receiver will be used with an orfice tube.
Typical Fan Switch
Typically Utilized with 1 piece Beadlock Type Fitting and Barrier Nylon/Rubber Hose
One Piece Beadlock Fitting
Also called (TXV) they may be one of two types, externally or internally equalized and they can be either right angle or block style. The expansion valve’s job is to properly meter the right amount of refrigerant entering the evaporator coil. You will find a drier/receiver when these types are used. To troubleshoot problems with the expansion valve you must have the proper set of refrigerant gauges attached to an operating A/C system.
Typical Orifice Tubes
BLOWER MOTORS & FAN WHEELS
Blower motors control the amount of air across the evaporator coil. If the motor rotation is not correct, or the motor, fan wheel, or resistor (if used) malfunctions, not enough air will be drawn across the evaporator coil and it may freeze up. Broken fan wheels or housing will cause the motor assembly to sound very loud and will need to be replaced. There are usually two types of motors used in a blower system, (Field Wound) it has 4 wires and operated by a fan switch only. Or a (Permanent magnet motor it has only 2 wires and requires a fan switch and a resistor always make sure you have the right motor and resistor for the voltage.
Also called a heat exchanger, the evaporator coil removes heat from the air that the fan motors pull in then discharges the cold air out of the louvers. The evaporator usually operates between 30 degrees and 40 degrees Fahrenheit and louver temperature is about 10 degrees warmer than the coil. Long duct work may increase the temperature a few degrees more. If the coil becomes plugged with dirt, mud or ice, the air being discharged from the louvers will get warmer. Blow out the coil with compressed air about (60-90 pounds) or wash the coil with water or coil cleaner to insure that there is good air flow thought the coil. Use a fin comb to straighten evaporator coil fins not a screwdriver.
Also called a heat exchanger- removes heat from refrigerant that is in very high pressure, high temperature state, by passing cooler ambient air over the condenser fins. This changes the state of the refrigerant from a gas to a liquid before going to the drier/receiver or accumulator. If the condenser fins get plugged with mud debris or even a fine coating of dirt you will have poor or no cooling out the louvers. Be sure to clean condenser coil with compressed air or wash with water or coil cleaner keep coil fins straight with a fin comb not a screwdriver.
FAN SWITCH & RESISTORS
You will find the fan switch located in the evaporator blower system as in a lot of your aftermarket A/C units, or in the cab console for drop in coils or OEM systems. The fan switch controls the blower motor speeds. On the back of most fan switches you will find five posts. “B”= power, “C”= clutch, “L”= low speed, “M”= medium speed, “H”= high speed. The resistor is used to cut the amount of current to the blower motor so you will have high, medium, and low it will be found in the blower unit that houses the blower motor. (See the section on blower motors & fan wheels for more information on resistors.)