• sw
    • The number of poles* on a switch defines how many separate circuits the switch can control. So a switch with one pole, can only influence one single circuit. A four-pole switch can separately control four different circuits.
    • A switch throw-count defines how many positions each of the switch poles can be connected to. For example, if a switch has two throws, each circuit (pole) in the switch can be connected to one of two terminals.

      AC system

  • heat movement
    • heat moves from a hotter area to a colder area.
    • conduction, convection, and radiation
  • heat measurement
    • intensity: \(C = (F - 32) * {5 \over 9}\)
    • quantity: BTU, J
  • latent heat (hidden heat) is the heat absorbed or given up upon changing state
    • vaporized @ vaporator(lower pressure): liquid +BTU (blow hot air in the cab to the vaporator) = vapour
    • condensed @ condenser (high pressure): vapor -BTU (fan remove heat) = liquid
  • @ low pressure, liquid boil at a lower temperature
    • low pressure - boiling vapour - compressed high pressure - liquid +BTU
  • superheat
    • require to assure the compressor is protected from liquid refrigerant.
    • compared low pressure side with evaporator outlet temp
    • specs 8 - 12F
  • subcooling
    • compared high pressure side with condenser outlet temp
    • specs 12-21F
  • refrigerant
    • common R-134a
    • mineral oil (MO) does not mix with R-134a (not compatible)
    • polyol ester (POE) & Polyalkylene glycol (PAG) can be mixed with R-134a
    • MO can not mix with PAG
  • AC events
    • expansion
      • liquid expanding from high pressure side 124psi(100F) to low pressure 30 psi (90F)
    • evaporation
      • pressure is lower, so liquid change to a vapor, thus absorbing heat
      • warm area cooled
    • compression
      • raise pressure and temp of the vapor
      • 124 psi, 220F
    • condensation
      • cool vapor to 100F
      • vapor change to liquid
  • heat it up => pressure increases
  • AC ref: http://www.central-air-conditioner-and-refrigeration.com/basic-refrigeration-cycle.html
  • pressure and boiling point relationship
    • lower pressure, lower boiling point
    • higher pressure, higher boiling point
  • perfect vacuum: 30, cannot get more than that
  • 30 in of Hg = 760,000 microns
    • 500 microns are expected
  • refrigerants
    • no color, slight odour
    • non-toxic, non corrosive, non-flammable
    • most common nowsaday, 1234yf (move around 55-60BTU/lb)
    • Duracool 12a or HC-12a (crap!), flammable
    • R-12 (freon) (50BTU/lb) ozone depletion (used mineral oil, use good hose), R-134a (90 BTU/lb) green gas
      • to change the use of R-12 to R-134a, we change the fitting, different size of orifice if needed
      • 1995 banned in North America
      • mineral oil based
    • r-134a (smaller molecues)
      • non ozone depletion
      • green gas gas contributor
      • lub: poly alkaling glycol (P.A.G) (seperated with refrigerants) (for hot environment)
      • poly ol ester (mix with everything, use for top off) (will get hot fast!)
  • accumulator have a hole to pick up oil circulating the system
  • condenser subcooling
    • proper change: 180in 150out
      • outlet temp: 20-50F cooler
      • subcool happens in condenser, dryer, hose
    • under charge: 180in 80out
      • the change of state is completing too far from the outlet
    • overcharge: 180in 180out
      • the change of state is not completed inside the condenser
      • subcooling is not happening inside the condenser
  • evaporator superheat
    • proper charge: 32-39F
      • outlet is 2-10F warmer for txv, 1-5F lower than inlet (32-29F) for ccot
      • the change of state is completing close to outlet
    • undercharge 32-62F
      • the change of state is completing too far from outlet
      • superheat in evaporator, suction
    • overcharge: 32in-29out (ccot 32-12F)
      • the change of state has not completed inside the evaporator
      • the eva does not warm the vol of refrigerant fast enough
  • txv does not have acc to prevent liquid enter compress, do not overcharge
    • expansion valve continuously monitor evaporator outlet, if it is too cold, then reduce orifice side
    • normal low pressure: 10-15psi
    • normal high pressure: 140-180psi
  • ccot does not have dryer
    • normal low pressure: 13-30psi
    • normal high pressure: 140-180psi

troubleshooting

  • need wiring diagram
  • run ac
  • identify refrigerant

  • bypass electrical see if it works

  • normal pressure (both high & low) (need to run 10-15 minutes)
  • colder than normal vent temp (old people complaint)
    • reduce the temperature on dash
  • warmer than normal vent temps
    • blend air door stick opened
    • water valve
  • low on low side/low on high side readings
    • under charge
      • identify
      • recover
        • low lbs (underweight)
        • look for leak by nitrogen test -> vacuum -> dye
        • repair leak
        • add oil if need
        • evacuate nitrogen
        • recharge
      • txv stick open, high pressure on low side
      • TXV: run constant, low side vacuum
      • CCOT: cycle once, off for a long time
    • blockage (on high side, from simulator)
      • can’t be right after compressor!
      • can block the orifice
      • TXV: run constant, low side vacuum
        • turn it off see if balance quickly. if it not cycle quickly -> blockage
      • CCOT: cycled quick
      • can look for frost spots as blockage act like a tight orifice
    • blocked air flow through the evap because of blockage evap
      • TXV: thermostatic sw may shut it off
      • CCOT:
  • high/low readings
    • compressor
      • clutch not engaging
        • electrical problems
      • reed valves
        • slugging will damage reed valves (charge with liquid)
          • improper charging (open the yellow ball handle open all the way)
          • overcharged
          • failed switches
      • not knowing how a gauge set works
  • high/high readings
    • overcharged
      • TXV : run (thermo sw may shut it down)
      • CCOT : run constant
        • acc will be frost
    • blocked air flow through condenser
  • expansion valve is easy to stick opened or closed, most of the time replace it, will work.
  • anytime service AC, replace descecant in acc or filter in receiver/dryer
  • condenser fan does work, pressure will increase

AC Control system

  • If Low pressure sw should be on low side, and High pressure sw should be on high side, we can not run ac system with low refrigerant.
  • If we have low refrigerant and low-high pressure sw (trinary) on high side, we can still run ac system
  • active control
    • engine coolant water valves
      • flow restricter located in engine coolant water valves slows the coolant down, so heat has time to transfer to the cab
      • seized open coolant water valve causes the truck cab to remain very warm even when the AC is operating
    • magnetic clutch
      • black coil lead wire: 12V
      • green coil lead wire: 24V
  • passive (automatic) control
    • thermostatic sw (NC, TXV):
      • adjustable can reach 50F for closing point
      • fixed sw
        • open @ 32F, disengage the compressor
          • when the evaporator core is closed to freeze temp, stop the compressor; the heat will warm and defrost any frozen moisture
        • close @ 38F, engage the compressor
          • when the evaporator core is warm, the sw closes the contact, engaging the compressor
    • low pressure sw
      • normally open valves
      • 24psi open; 34psi close
      • located in low side on acc, protect compressor from low refrigerant pressures due to blocked expansion valve or lack of refrigerant
      • located in high side on receiver/dryer, sense low pressure from high side and ambient temp is too cod
    • clutch cycling sw (NO, a low pressure sw replace thermostatic sw on CCOT)
      • protect compressor from operating with low refrigerant pressure & no oil circulation
      • located on accumulator
        • open @ 24psi (34F), disengage compressor, defrost evap
        • close @ 48psi (39F), engage compressor, cool evap
      • can have diff range [12, 38] or [24psi, 48psi]
    • high pressure cut-out sw, (NC)
      • open @ 350psi, stop compressor
      • close @ 250psi, start compressor
      • sense high side
      • must lower than pressure relief valve (fusible plug)
      • can use to control condenser fan & radiator shutter systems
        • condenser fan kick in when condenser does not receive enough cooling ram airflow to keep the pressure with normal limits
    • binary sw (low/high pressure sw)
      • provide slow and high pressure protection
      • located bw condenser and expansion device (on dryer)
    • trinary sw
      • located bw condenser and expansion device (on dryer)
      • low pressure sensor (NO):
        • open @ 15-28psi
        • close @ 40psi
      • high pressure sensor (NC)
        • open @ 270-330psi
        • close @ 80-125psi
      • mid range: (NO) controls condenser fan
        • open @ 35-60psi
        • close @ 200-230psi
    • refrigerant solenoid valve
      • direct refrigerant to second evaporator’s expansion device
      • open when sleeper compartment call for cooling and cab has to be in operation
    • blower motor and fans
      • “single or double shaft” motor
      • “single or double entry” blower wheels
  • AC management system
    • control module
    • monitor (input)
      • high / low pressure
      • thermostatic sw
    • control (output)
      • condenser fan (how long is engaged depending on vehicle speed and how high the pressure is)
      • compressor clutch
  • automatic temperature control
    • monitor (input)
      • cab temp sensor
      • fresh air temp sensor
      • evaporator temp sensor
    • control (output)
      • heater water valve
      • blower fan speed
      • compressor clutch
  • manual climate control HVAC system (temperature blend air door system)
  • air distribution system
    • settings
      • fresh air door setting: recirculation and fresh air
      • temp setting: red and blue
      • airflow direction: panel, panel & floor, floor & defrost, and defrost
      max cooling max heating max defrost normal cooling floor and defrost heating cab ventilation
    blow speed max max max lowest second speed second speed
    heater water valve closed opened opened partly opened opened partly opened
    fresh air intake closed closed closed opened closed opened
    cab recirculation air inlet opened opened opened closed opened closed
    panel outlet opened opened closed opened closed opened
    floor outlet opened opened closed closed opened opened
    defroster outlet closed closed opened closed opened closed
    compressor clutch engaged disengaged engaged engaged disengaged disengaged
    AC sw on off off on off off
  • sleeper compartment
    • heating: electronically controlled coolant valve installed on return side of coolant on sleeper side
    • cooling: electric refrigerant solenoid valve installed after dryer on sleeper side
    • fuel-fired air heater (draw 2A/hour) use to reduce premature engine wear on parking truck for sleeping
    • fuel-fired coolant heater
      • draw dc
      • help engine start up
      • warm sleeper compartment
      • some sense battery voltage and not operate if less than 10.5V
    • aux power units
      • warm by heat from aux engine
      • cool by aux driven air ac compressor
  • use fuse protected jumper wire override the low pressure sw, if clutch engages
    • low refrigerant
    • faulty low pressure sw
    • the refrigerant is too cold to create enough pressure to closed the sw