Gary May Heating and Air Conditioning
Spartan Chassis Air Conditioning & Maintenance
Principles of HVAC Basic Components and their functions EPA requirements of safe handling Diagnoses of HVAC systems pressure readings. Service tips Course Outline
The Basic The Basic Principles of Air Conditioning Principles of Air Conditioning
In a solid, molecules are locked together in position. In a liquid, molecules move and share a loose relationship with each other. Molecules in a gas, share no relationship with each other because they move very fast. Heat, commonly described in degrees of temperature, such as Fahrenheit (o F) or Celsius (o C), describes the random motion or “vibration” of molecules. When a substance becomes hotter, its molecules move faster. How fast these molecules move determines whether the substance is a solid, a liquid, or a gas. Principles of HVAC
Principles of HVAC
When a fast, hot molecule collides with a slower, colder molecule, like a fast car colliding with a slower car…. The slower molecules speeds up (it becomes hotter) like the car, but never as fast as the car that hit it, and it “cools” the faster car, too. Heat always goes from hot to cold because a slower molecule cannot make a faster molecule go faster! Have you ever heard of a car going 15 MPH catching up to and hitting a car going 30 MPH? Principles of HVAC
Removing heat is simple. Since heat always goes toward a colder object, all we have to do is give heat a cold thing to flow into. A good example of this is a iced drink. To cool the drink down, we put in ice cubes. Since ice cubes are colder than the worm liquid, the heat will flow into the ice cubes. The ice cubes absorb the heat and melt, removing the heat from the liquid. Now the drink is much more enjoyable. How A/C Works
Principles of HVAC Heat always goes to cool
Principles of HVAC Low pressure gas Hi Side Out Put need to increase temperature about 21/2 times over ambient Hi pressure gas
Remember that raising the refrigerant pressure is necessary to begin the process of rejecting heat into the outside air. On it down stroke the compressor piston collects the expanded refrigerant inside the compressor. On its up-stroke the piston forces the refrigerant molecules closer together. The refrigerant vapor is raised in pressure, temperature and boiling point before being forced out of valve plate assembly. The temperature of the vapor is normally two and a half time higher than the temperature of the outside air. Since heat always flows hot to cold, the refrigerant must be much hotter than the outside air to be able to move heat out of the system. Compression Heating
Looking at this in a different way a truck cooling system would boil at 212 Deg. when a 16 lb. radiator cap is installed coolant will boil at 252 Deg. The pressure of the system at 16 lb. raises the boiling point because it compresses the molecules and limits there ability to move this raises the boiling point of the coolant. Compression Heating
The hot, high pressure vapor makes its next stop at the condensing coil. The condenser is just like the evaporator-it is a heat exchanger. It looks a little different from a evaporator because it is more flat and a little larger Inside the condenser coil, the gas starts it way from the top to the bottom, cooling down a little with each pass. By the time the refrigerant reaches the lower third of the coil, it cools down enough to change back into liquid, it continues to cool 15-30 deg. F. below its boiling point in a process called “sub cooling” Sub cooling is an important concept to understand because it will tell what is wrong with the high side of the system. Sub Cooling
Principles of HVAC 180 deg. to 240 deg. gas Liquefied gas Liquid 135 deg. to 180 deg.
Principles of HVAC Install in correct directio n
The expansion device creates a pressure drop by restricting the flow of refrigerant around the system. Slowing down the flow of refrigerant caused the compressor to partially evacuate one side of the system. This low pressure void is called the “Suction side” or the “Low side” of the system. Side the low side has a very low pressure, the refrigerant can begin to boil off into a gas. When the refrigerant changes from liquid to gas it gathers heat from the cab air. The pressure difference is created by an expansion device. Principles of Expansion
Principles of HVAC
The 5 basic components of a/c Compressor Condenser Expansion device Receiver dryer Evaporator Diagnostics Of A/C Systems
How A/C Works 180 psi to 240 psi 18 psi to 26 psi 140 psi. to 180 psi
Cold referent absorbs heat from cab air while the reorient circulates inside the evaporator coil. Heat from the cad air passes through the metal of the evaporator and causes the reorient to expand by boiling off into a vapor. This boiling is possible because referent used in AC systems have a boiling point of about one pound per square inch per 1deg. F. For example, the boiling point of refrigerant is approximately 20 deg. F. at 20 psi. As the refrigerant expands by boiling into a vapor, it takes massive amounts of heat with it. Low-Side Operation
Expansion Valve Operation
Principles of A/C
Air Conditioning Basics: Air Conditioning Basics: Major Components Major Components
Pressure Relief Valve Replaced Fuse Plug (melt bolt)
Compressor 10 P Type Compressor
Clutch on Spartan has 5.5 amp draw
Compressor Oil / Pag 100
Condenser
Condenser
Condenser Fans Fan draw 8.5 amp each
Dual Pressure Binary Switch / Opens 392 psi high 29 psi low Pressure switch is installed on the liquid tube between the receiver drier and expansion valve. If abnormally high pressures (or low pressures) are detected, the contacts open. This interrupts the ground to the magnetic clutch relay. Clutch is disengaged.
O-Rings The O-rings of the piping connectors that are used in CFC-12 air conditioning systems and those that are used in HFC-134a systems ARE NOT INTERCHANGEABLE. O-rings for CFC-12 systems used in HFC- 134a systems will foam and swell, resulting in leakage of refrigerant.
Receiver Drier Caution Install in correct direction
Major Components Front & rear Thermostats Liquid Solenoid Valve 3 Amp fuse Heater control valve Evacuation Pump
Picture of bilge pump fuse location Bilge pump fuse location
Condenser breakers Breaker replace with max fuses
Evaporator Condenser Pump
The evacuation pump works independent of A/C. Power is supplied by IGNITION. Pump runs any time ignition is on. Internal timer will run pump as long as there is water present then shut off. Then restart about every 2 minutes.
Tools: Tools: Refrigerant Refrigerant Recovery/Recharging Machine Recovery/Recharging Machine Leak Detector Leak Detector
Refrigerant Recovery/Recharging Machine
Service Precautions: Service Precautions: Refrigerant Handling Refrigerant Handling Environmental Regulations Environmental Regulations
R134A cylinder is Light Green (Teal) High side hose is Red with Black stripe. Low side hose is Blue with Black stripe. Service hose is Yellow with Black Stripe All A/C hoses must have manual shut off with in 6” of the service port end. Environmental Regulations
Environmental Regulations
Refrigerant Handling When tightening connecting parts: Apply a few drops of compressor oil to O-ring fittings for easy of tightening and to prevent leaks. Use a backup wrench to avoid twisting the tube.
connections to specified torque Refrigerant Handling • Tighten
An undercharged system will provide inadequate lubrication to the compressor. Charge a system that is operating through the low-pressure side only. Refrigerant charged to an operating system must be in gas form only. An overcharged system can cause inadequate cooling, poor fuel economy and engine overheating. Refrigerant Handling
On-Vehicle Inspection: On-Vehicle Inspection: Troubleshooting Troubleshooting Evacuation & Charging Evacuation & Charging Performance Test Performance Test
All Spartan fire truck systems have die installed at the factory Use a black light and yellow glasses to detect leaking. Look for spray patterns not finger prints from installation. Leak Detector Use Black Light
V-Mux Diagnostics
Spartan Chassis needs the following first in order to best direct you to Spartan or OEM for assistance. SO# _______ Mileage _________ Verify customers complaint. Check for proper voltage to compressor. Record ambient air temperature at time of diagnosis. . Fire Truck A/C Diagnoses
Check static pressures and record both hi and low gauge reading the same Check running high and low pressure at idle and record. Check high and low pressure at hi idle and record. Fire Truck A/C Diagnoses
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