What Makes Car Air Conditioner Blow Warm Air Instead Of Cooling

What Makes Auto Air Conditioner Blow Warm Air Instead Of Cooling

What Makes Auto Air Conditioner Blow Warm Air Instead Of CoolingIs your vehicle’s air conditioner blowing warm air only and no cool air? Your Air Conditioner cooling issues could be caused by one of the following:

Your A/C system might have lost its charge of refrigerant. This is likely the most common cause of a no cooling issues. Another possible cause of no cooling may be that your A/C compressor is not engaging when you turn on the A/C. This can be caused by an electrical fault in the A/C compressor circuit or the magnetic clutch that drives the compressor. Another possible cause could be an internal obstruction inside the refrigerant circuit that is keeping refrigerant from circulating inside the A/C system. Another possibility might be a blend air door inside the HVAC unit that is either stuck in the HEAT position and is keeping air from flowing through the A/C evaporator.

Begin with the compressor. Does it actually engage when you turn on the A/C?

If so, the compressor might be working and the A/C system probably has enough refrigerant to make cold air, so the issue is inside the HVAC unit. Change the motor that controls the blend air door (this is a complex job and best left to a professional since it involves opening apart the HVAC unit — about an 8 to 10 hour job!).

If the compressor does not engage when you turn on the A/C, check if it will run by jumping the compressor clutch wire directly to the battery (use a fused jumper wire). If the compressor works when you jump it, and the A/C blows cold air, the system contains refrigerant and the fault is probably a bad A/C compressor clutch relay or a bad clutch cycling switch or pressure switch.

If the compressor does not engage during jump it, the issue is a bad compressor clutch.

If the clutch engages but the compressor does not turn (the belt will begin to slip and squeal), the compressor is locked up and you require a new compressor.

If the compressor clutch engages and turns the compressor, but the A/C still does not blow cold air, the system is likely low on refrigerant and has to be recharged.

Refrigerant Checks

Attach an A/C pressure gauge to the HIGH SIDE service port (found in the high pressure hose that passes between the compressor and the condenser in the front of the engine section). The gauge will tell you if there is any pressure in the system. Simply depressing the service fitting valve with a small screwdriver to see if any refrigerant squirts out is NOT an accurate check since it only tells you how much pressure is in the system. It may still have some pressure but not enough to trip the low pressure safety switch in order for the compressor to engage.

If your A/C system gets low or out of refrigerant, inspect for leaks, then have the A/C system vacuum purged to take out air. After the air is out, it can be recharged with the specified quantity of refrigerant. It is vital to get any air out as this will lower the cooling efficiency and may make the compressor noisy.

A/C System Functional Inspection

If the refrigeration circuit appears to be working (refrigerant in the system, compressor running and building pressure), but there is still no cooling, the issue might be an obstruction in the orifice tube (found in the high pressure hose between the condenser in the front of the radiator, and the evaporator found on the passenger compartment). A blockage here will stop the refrigerant from entering the evaporator or reticulating via the refrigeration circuit.

If the orifice tube is plugged, the high side pressure reading will get lower than normal, and the low side reading will also be lower than normal since no refrigerant is circulating through the system.

If the refrigeration circuit appears to be functioning normally (compressor running, frost or condensation on the high pressure line from the condenser to the evaporator), but no cool air is blowing out of the ducts inside the vehicle (and the blower is working), the fault is likely a BLEND AIR door that is stuck in the HEAT position, or probably a badly clogged cabin air filter that is stopping airflow. Another possibility would be a fault in the automatic climate control system such as a ad interior temperature sensor or control module.

I advice that if you know nothing about A/C service, find a repair shop that specializes in A/C repairs and let them diagnose and fix your air conditioning cooling issue. Modern A/C systems with automatic climate control are very complex and need special tools and know-how to diagnose and fix.

A/C Gauge Readings

To know the HIGH SIDE and LOW SIDE pressures inside your car’s air conditioning system, you require an A/C Gauge Set. The Gauge Set must be linked to the A/C service ports on car to read the pressures while the system is running.

With the engine OFF, connect the A/C Gauge Set High Pressure Hose (the one that has the larger coupler fitting) to the High Side service port (often located in the compressor output line that goes from the compressor to the condenser). Connect the Low Pressure Hose (the one with the smaller coupling) to the Low Side Service port (usually found on the accumulator, or on the suction hose that goes from the evaporator to the compressor).

Start the engine, turn on the A/C to MAX, and rev the engine to 2000 RPM. Hold the engine speed and observe the High and Low side pressure gauge readings.

NOTE: High and Low side pressure readings will differ with ambient temperature and humidity. The higher the temperature and/or humidity, the higher the gauge readings.

With late model R134a systems, good high pressure readings should begin from 150 to 220 PSI at 80 degrees F, 170 to 250 PSI at 90 degrees F, and 195 to 280 PSI at 100 degrees F.

A High side pressure reading of less than 150 PSI shows a low charge or a compressor problem. A high pressure reading over 300 PSI would show an overcharge condition (too much refrigerant in system) or a restriction in the high side.

Good low pressure readings with R134a should often be in the 30 to 35 PSI range. If higher, there may be a low side restriction. If the reading is actually lower, the system may be low on refrigerant.

With older R12 A/C systems (1994 model year cars an older that have NOT been retrofitted to R134a), the HIGH side pressure readings will normally be 150 to 185 PSI at 80 degrees F, 175 to 205 PSI at 90 degrees F, and 200 to 250 PSI at 100 degrees F. Normal LOW side readings with R12 should range from 20 to 30 PSI for an expansion valve system, or 15 to 40 PSI for an orifice tube system.


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