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Refrigeration Circuit Troubleshooting
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1. If the pressures are normal, or the customer complains of insufficient cooling, check for: A) A misadjusted, leaking or mis-plumbed water control valve (this valve won't seal if plumbed backwards. Both the inlet and outlet hoses at heater core should feel cool. If either one or both are hot, the valve is leaking; it doesn't take much coolant flowing through the heater core to get warmer air). B) The fresh-air door - not closing sufficiently to prevent entrance of warm air. 2. If the compressor is not operating, check for the following malfunctions: A) An undercharged system (first check for leaks, and then evacuate and recharge the system) B) A bad pressure switch C) A faulty control head selector switch D) A faulty thermostat, or possibly a sensing bulb dislodged from the evaporator core. 3. Problems indicated by extremely high pressure readings on the suction side follow: A) A faulty expansion valve (these rarely go bad; more frequently the sensing bulb is not insulated properly or secured to the outlet pipe of the evaporator) B) An overcharged condition (if water is run over the condenser and a reduction in suction side pressure is observed, this indicates overcharging; some refrigerant will have to be reclaimed from the system) C) A faulty valve in the compressor (in this rare, but possible case, there will be only a slight variation in both the suction and discharge readings at any engine speed) 4. Extremely high discharge pressure reading suggest the need to check the following: A) Condenser for cleanliness or for damaged fins B) Pressure switch or condenser fan fuse C) Fan clutch or relay 5. Extremely low suction side pressures signal these possibilities: A) An undercharged system (if there are bubbles in the sight glass, check for leaks, evacuate, and recharge B) Receiver-drier desiccant possibly contaminated with moisture or a line restriction C) Expansion valve stuck closed 6. Low discharge pressures may mean that: A) The system is undercharged. (Observe the sight glass with the control set at "MAX" and engine running above 1600 rpm. There should be a cloudy stream of liquid flowing without any bubbles) You will need to be proficient with a manifold gauge set in order to effectively troubleshoot the refrigeration circuit; It is important to note here that it is vital to have a clean radiator and condenser, to have belts adjusted properly, and the fan clutch operating properly, if so equipped. Otherwise, poor airflow would cause a significant increase in both low and high side pressures. There are other situations that might be encountered, but these are the most common things found when diagnosing dash air conditioner problems. A few added words of advice: It is important to wear safety glasses and protective clothing when working on these components in the evacuation and recharge cycle. Don't smoke or expose discharge refrigerant to an ignition source. You must use a refrigerant reclamation machine. |
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