Troubleshoot Your Car Air Conditioner Not Blowing Cold Air

Cooling System

By Rodney (Mechanics)

Table of Contents

If your car air conditioner is not blowing cold air, you may wonder what the problem is and how to fix it. There are several common causes for this issue, and sometimes some problems are easily resolved with a little troubleshooting. We will go over some common causes of a car air conditioner not blowing cold air and provide tips for troubleshooting and fixing the issue. Whether you’re an experienced mechanic or a novice car owner, this guide will help you fix the A/C issue you may have.

The most frequent reason for an A/C system, not cooling could be that it has lost its refrigerant charge. If the A/C compressor does not engage when you turn on the A/C, it could also be another possible cause caused by an issue with the electrical circuit of the A/C compressor or the magnetic clutch that drives the compressor. An obstruction inside the circuit may also prevent refrigerant from circulating within the A/C system. Alternatively, a blend air door in the HVAC unit that is stuck in the HEAT position could be another possibility, preventing air from flowing through the A/C evaporator.

AC Gauge R134a

Compressor Checks

When you turn on the A/C, does the compressor start engaging?

If the compressor engages when you turn on the A/C, it is functioning and has sufficient refrigerant to produce cold air. Therefore, the issue could be with the HVAC unit, and you may need to replace the motor controlling the blend air door. Since this is a complex task involving dismantling the HVAC unit, it’s best to leave it to a professional. It could take around 8 to 10 hours to complete.

If the compressor fails to engage when you turn on the A/C, you can try directly jumping the compressor clutch wire to the battery (using a fused jumper wire). If the compressor runs and cold air blows, the refrigerant is sufficient, and the problem is most likely due to a faulty A/C compressor clutch relay, pressure switch, or a bad clutch cycling switch.

If the compressor fails to engage even when jumped, it indicates that the problem is with the compressor clutch, which needs to be replaced.

When the clutch engages, but the compressor fails to turn (and the belt slips and squeals), the compressor is likely locked up, and a new one is necessary.

If the compressor clutch engages and rotates the compressor, but they’re still no cold air, it is probable that the refrigerant level is low and needs to be recharged.

Check the refrigerant level, and attach an A/C pressure gauge to the service port on the HIGH SIDE. The port is between the compressor and the condenser at the front of the engine compartment (on the high-pressure hose). You cannot rely on depressing the suitable service valve with a small screwdriver to check the pressure since it will not show the actual pressure level in the system. The gauge will provide an accurate reading.

HighSide Low Side

If the A/C system is low or out of refrigerant, look for leaks, then have the system vacuum purged to remove air. After the air is removed, recharge it with the required refrigerant. Eliminating air from the system is crucial to increase cooling efficiency and prevent compressor noise.

If the refrigeration circuit appears to be functioning correctly (refrigerant in the system, compressor running, and pressure building), but there is still no cooling, the obstruction may be in the orifice tube located in the high-pressure hose between the condenser in front of the radiator and the evaporator in the passenger compartment. If there is a blockage, the refrigerant cannot enter the evaporator or circulate through the refrigeration circuit.

If the orifice tube is obstructed, both high and low side pressure readings will be lower than normal due to the lack of refrigerant circulation.

When the refrigeration circuit appears to be functioning correctly (compressor running, a high-pressure line showing frost or condensation), but cool air is not coming out of the car’s ducts (and the blower is operational), the cause is likely a BLEND AIR door that is stuck in the HEAT position or a clogged cabin air filter that obstructs airflow. A potential cause could be a problem in the automatic climate control system, such as a faulty interior temperature sensor or control module.

If you do not know A/C service, it’s best to seek out an A/C repair shop specializing in these repairs to diagnose and fix your A/C cooling problem. Modern A/C systems with automatic climate control are highly complex and necessitate specialized tools and expertise to diagnose and repair.

Diagnose Air Conditioning Problem Chart

A/C Gauge Readings

To determine the pressures within your vehicle’s air conditioning system, you will need an A/C Gauge Set, which must connect to the A/C service ports while the system is running.

To start, turn off the engine and connect the High Side service port to the A/C Gauge Set High-Pressure Hose (the one with the larger coupler fitting), which is usually located in the compressor output line from the compressor to the condenser. Connect the Low Side Service port to the Low-Pressure Hose (with the smaller coupling). You can find the port on the suction hose, which goes from the evaporator to the compressor or the accumulator.

Once you have made the connections, start your engine, turn the A/C on, set it to MAX, and rev the engine until 2000 RPM. While holding the engine speed, note the High and Low side pressure gauge readings.

It is important to note that the High and Low side pressure readings will vary depending on the ambient temperature and humidity. As the temperature and humidity increase, so will the gauge readings.

For late model R134a systems, high-pressure readings should range from 195 to 280 PSI at 100 degrees F, 150 to 220 PSI at 80 degrees F, and 170 to 250 PSI at 90 degrees F. There indicates a low charge or a compressor problem when a High side pressure reading of less than 150 PSI means an overcharge condition or a restriction on the high side, while a high pressure reading over 300 PSI.

Low-pressure readings with R134a should usually be in the 30 to 35 PSI range. If the reading is higher, there may be a low side restriction, and the system may be low on refrigerant if the reading is lower.

For older R12 A/C systems (1994 model year vehicles and older that have NOT been retrofitted to R134a), the HIGH side pressure has reading results of 200 to 250 PSI at 100 degrees F, 175 to 205 PSI at 90 degrees F, and 150 to 185 PSI at 80 degrees F. Normal LOW side output with R12 should be around 15 to 40 PSI for an orifice tube system or 20 to 30 PSI for an expansion valve system.