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Heating & Air Conditioning

 

 

Overview

 

   

Refrigeration Cycle

  • Compressor
    • It sucks low pressure gas and pressurizes it more on the discharge line
  • Condenser
    • Condenses gas into liquid due to drop in temperature.
      • With high temperature, gas molecules move faster and need more space for movement.
      • With temperature decreasing, molecules move slower and thus need less ‘working  space’.
      • When gas temperate below its dew point, ‘working space’ of molecules becomes dense enough which transitions gas into liquid.
    • Inlet/Outlet temperature difference should be 20F-40F.
      • Less than 20F might indicate airflow problem.
      • More than 50F indicates condenser restriction.
  • Orifice Tube or Thermostatic Expansion (TEV or TXV)
    • Releases high pressure liquid into lower pressure environment
    • On a low pressure side it still remains a liquid (until it warms up)
  • Evaporator
    • Performs heat transfer.
      • Hotter air outside the evaporator warms liquid refrigerant inside  and because refrigerant’s boiling point is low ( −26.3 °C  or −15.34 °F at atmospheric pressure), it starts to boil and turns into gas at evaporator’s outlet. Thus, gas takes heat away from evaporator.
      • If pressure of the refrigerant on a low side is too low, evaporator might freeze. Thats why compressor won’t turn on because of low pressure (typically 3-33 psi).
        • Water boiling
          • Stove heats water until its boiling point (depends on atmospheric pressure).
          • Bubbles of vapor start to form which are immediately replaced by the colder (heavier) molecules from the top (due to gravity, buoyancy).
          • These bubbles transfer heat from the bottom to the top of the pot.
          • At first, bubbles get trapped at the denser, relatively cooler surface water, but when inner pressure overcomes atmospheric pressure, there is no more air resistance that prevents bubbles from vaporizing in the air.

 

Re-Charging A/C

  • Evacuate A/C refrigerant into machine
  • Evacuate moisture and air by using a vacuum pump
    • Let it vacuum for 15-30 mins
    • Before shutting the vacuum pump, close manifold valves
    • Check for leaks. Let it sit for another 30 mins.
  • Liquid Charge
    • Don’t ever put liquid through the LOW side. It will damage compressor. He designed to pump gas, not liquid. Plus liquid can take all the oil from the compressor.
  • Gas Charge (recommended)
    1. Start charging refrigerant gas through a LOW side.
    2. Watch pressures (idle)
      • High Side
        • Should be approx. twice the ambient temperature + 50psi. So 90 degrees F will need 230 psi
      • Low Side
        • Around 30 psi at 90F
    3.  Oil.
      • If replacing A/C pump you will have to drain and then add oil according to manufacturer specifications.
      • If replacing some other major A/C component, you might want to add a little bit of oil.
      • If all system is recovered, you might add around 2oz of oil. Some say its not required because percentage of oil in the gas form is very small.
      • How to add oil.
        • With A/C machine. A/C machine does it automatically when charging the system.
        • Without A/C machine. Unhook the service hose (middle yellow)  and pour oil inside the hose.

A/C Compressor Failure Causes

  • Worn belt that slips and overheats compressor
  • Overcharged
  • Loss of oil
  • Restricted line
  • Clogged cabin filter
    • Clogged cabin air filters can restrict air flow through the evaporator. This may result in refrigerant that does not flash fully to a gaseous state. Liquid refrigerant is captured by the accumulator, but with insufficient air flow, there may be an overflow. Any liquid refrigerant that reaches the compressor will soon cause damage.

 

R1234yf

  • Retrofitting Oil
    • Once A/C systems have been upgraded to R1234yf type refrigerants, A/C Compressors pre-filled with ND-oil 8 can no longer be used in the system!
      • When R1234yf type refrigerant comes in to contact with ND-oil 8, it will decompose and resin parts of the A/C system will start to deteriorate, so it is never recommended to use ND-oil 8 in combination with R1234yf type refrigerant.
      • The new ND-oil 12 (Denso) can be used in R134a type refrigerant systems, without needing to flush the system and remove the remaining ND-oil 8 from the A/C system, though technicians must make sure there is no dirt in the A/C system.
  • Retrofitting freon
    • The EPA staff has explained at various SAE International forums that topping off/filling a vehicle system designed for R-1234yf, which has received emission credits, with any refrigerant other than R-1234yf, is considered “tampering with a vehicle emissions-control device.” This is a violation of Section 203 of the Clean Air Act.
    • Use of another refrigerant (Including R-134a), due to the refrigerant circuit control calibrations, will cause the system to operate differently than it did in the design certified vehicle using R-1234yf.
    • The mixing of R-134a with R-1234yf will change refrigerant pressure and may result in evaporator freeze-up on pressure control systems, reducing system airflow.

 

Troubleshooting

 

A/C Clutch Does Not Engage

  • Normal conditions when A/C clutch might not engage
    • Low Idle
    • Hard Acceleration
  • Pressure Inputs
    • Low A/C pressure
      • E.g. Chrysler 200 needs at least 60psi before it will operate A/C clutch
    • High A/C pressure
  • Temperature Inputs
    • Low evaporator temperature
    • Ambient Temperature Sensor (10’ G37, …)
      • 📎 A/C Inop | Ambient Temperature Sensor | 2013 Chevy Sonic
        • Unplugged Ambient Temperature Sensor prohibited A/C operation. But even when it was plugged, A/C wouldn’t work.
        • I had to go to Instrument Cluster → Special Functions and perform Relearn CAN devices on a network. Only then temperature sensor started to show correct temperature and A/C started to work.
    • IAT signal
    • ECT signal
      • High engine coolant temperature
      • Missing ECT signal
        • 📎 A/C Inop. | Bad instrument cluster | 2006 Acura RL
    • Missing message from the A/C module
      • 📎 Blower Inop. | Bad A/C Module | 2012 Toyota Prius
        • Blower speed buttons, off button, change inlets doors buttons stopped working.
        • Blower speed could be regulated by the scanner.
        • Turned out to be a bad A/C control module.
      • Incorrectly Programmed/ Faulty IPC Instrument Cluster (Ford, Chevy)

Stuck on Blowing Hot or Cold Air

  • Blend Air Flap / Air Mix  Actuator
    • Make sure to put Air Mix Actuator is mounted on the housing.
      • Otherwise it might travel beyond the stopping point that the temp door would allow it to, and HVAC module, seeing out of limits condition, will not want to calibrate or operate it anymore.
      •  2002 Silverado 6.6L B0414 Air Mix Actuator Range/Performance
  • No Signal from Inside Air Temperature Sensor  (2000 ML320)
    • Inside Air Temperature Sensor helps to prevent over freezing

 

Blower Motor Issues

 

 

Pressure Check

  • Normal

    • High Side
      • Should be approx. twice the ambient temperature + 50psi. So 90 degrees F will need 230 psi
      • Or ambient temperature + 100 = high side pressure
    • Low Side
      • Around 30 psi at 90F
    • Static Pressure
      • High and Low Side should both read around 78psi at 75F.
    • Test for Restriction in the System
      • Operate A/C system for 5-10mins.
      • Shut off the car and watch pressures. They should equalize pretty quickly, if there is no restriction.
        • To find restriction, observe temperatures along the system lines. The restriction exists at the point of greatest temperature difference.
    • Fire Extinguisher Test (testing TEV)
      • Start engine and set A/C into recirculate.
      • Using CO2 extinguisher, blast the expansion valve with CO2.
      • If low side doesn’t go into vacuum, then expansion valve is faulty.
    • Heater Control Valve (Jaguar, BMW)
  • Abnormal

    • Low Side is LOW, High Side is too HIGH
      • Restriction
        • Clogged orifice tube
          • The high-side pressure may be elevated as the compressor attempts to force the refrigerant past the obstruction. This will quickly starve oil flow to the compressor and cause a catastrophic failure.
    • Low Side is LOW, High Side is LOW
        • Low on charge
        • Bad RCV (Refrigerant Control Valve) inside the compressor

 

    • Low Side is  HIGH, High Side is EQUAL to LOW SIDE
      • Bad RCV (Refrigerant Control Valve) inside the compressor
    • Low Side is  HIGH, High Side is LOW
      • Too much refrigerant is flowing in the evaporator
        • The TXV is stuck open or the thermal bulb is not sensing the temperature correctly.
        • The orifice tube is too large of an opening or the o-ring sealing the outside of the orifice tube is not sealing.
      • Bad compressor. Not sucking from a low side and not pushing enough into a high side.
    • Low Side is  HIGH, High Side is HIGH
      • ECM Strategy
        • ECM Software
          • ECM doesn’t turn off compressor at proper high side pressure limit
        • Faulty A/C Pressure Sensor (showing less pressure than it is)
      • Lack of airflow
        • Test. Inlet/Outlet temperature difference should be 20F-40F.
          • Less than 20F might indicate airflow problem.
          • More than 50F indicates condenser restriction.
        • Dirty condenser fins
        • Cooling Fan
          • Make sure the fan blows on the engine.
            • One fan (dual fan) blowing in the wrong direction caused 100-150 psi increase.
        • A worn fan-clutch or debris blocking air flow through the condenser will cause the same issue.
      • Blockage inside the condenser
        • Test. Inlet/Outlet temperature difference should be 20F-40F.
          • Less than 20F might indicate airflow problem.
          • More than 50F indicates condenser restriction.
      • Low side pipe is too hot to touch. Bubbles are seen through the glass.
        • Air present in the system
          • check compressor oil (dirty or in sufficient)
          • evacuate and charge new refrigerant
      • Low side pipe has frosts and condensation
        • Excessive refrigerant in low pressure piping
        • Cooler expansion valve is opened too wide
          • Replace cooler expansion valve

 

Hose Temperature Check

  • Preliminary Checks: Pressures are normal (low and high side) and the temperature of the air from the vents is not low enough.
  • Touch low side
    •  Cold
      • If cold, it suggests the problem likely exist under the dash, with the actuators or doors. Often, a temperature door malfunction will allow the cooled air to be reheated.
    • Hot
      • Low side pipe is too hot to touch. Bubbles are seen through the glass.
        • Air present in the system
          • check compressor oil (dirty or in sufficient)
          • evacuate and charge new refrigerant
    • Has frosts and condensation
      • Excessive refrigerant in low pressure piping
      • Cooler expansion valve is opened too wide
        • Replace cooler expansion valve

 

 

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