For you to understand to read the pressure gauges in your car’s air conditioning system, you should have a basic understanding of the AC. Fortunately, this article is a basic guide for reading the gauges to understand when your r134 is operating in Low Side Pressure. The guide can be used as a diagnostic tool for most, but not all cars. Often, the temperature and the pressure rise and fall simultaneously. Therefore, you need to understand the pressure changes in your vehicle’s AC.
Usually, it can take up to 15 minutes for the pressure in your AC to be equal at about 130 psi, depending on your vehicle’s make. However, the low-pressure gauges are unpredictable, which makes low-pressure diagnoses in the vehicle’s system troublesome. Therefore, it is important for you to tell the difference between low-pressure diagnostic procedures from the high-pressure ones. This guide is a fact sheet for people when handling the R134a AC system. Nonetheless, it is worth noting that newer vehicles’ refrigerant system is markedly different for older models.
How to Read the R134 Pressure System for Newer Models of Cars
Typically, the optimal operating pressure for the AC refrigerants lies between 23 and 57 pounds psi. Since the r134 is the most widely used refrigerant in the 21st century, this article will illustrate how to read the AC pressure system to determine when your vehicle is operating at low side pressure.
The r134a, commonly known as the HFC-134a (Hydrofluorocarbon – 134a), is readily available in the motor industry market. In the United States, it is illegal for one to vent the HFC refrigerant into the atmosphere. Therefore, you should know the basic do-it-yourself procedures that restore your car’s AC system’s functionality at different temperatures and pressures.
In most vehicles, there are different gauges to measure the compressor pressure. The blue one displays the low-pressure readings, while the red one shows the values when the pressure is high. There is no clutch plate or knob for automatic climate control to control the quantity of refrigerant flowing into the AC system. Therefore, the pressure is automatically controlled by sensors in the ECU.
When the temperature is optimum, the system will reduce the amount of refrigerant moving into the system if the pressure reading on the blue gauge falls below the optimum readings on the compressor’s suction side. Some of the possible causes of this malfunction include a blockage on the filter, too much oil in the system, a blockage on the thermal expansion valve, or a broken pipe, among many other causes. Below is a chart showing the low-pressure readings and their corresponding ambient temperatures in newer models of automobiles.
R134a Temperature-Pressure Chart
| Temperature Readings (0F/0C) | Low Pressure Gauge Readings |
| 650F/180C | Between 25 to 35 psi /172-241kPa |
| 700F/210C | Between 35 to 40 psi /241-276kPa |
| 750F/240C | Between 35 to 40 psi /241-310`kPa |
| 800F/270C | Between 40 to 50 psi /276-345kPa |
| 850F/290C | Between 45 to 55 psi /310-379kPa |
| 900F/320C | Between 45 to 55 psi /310-379 kPa |
| 950F/350C | Between 50 to 55 psi /345-379kPa |
| 1000F/380C | Between 50 to 55 psi /345-379 kPa |
| 1050F/410C | Between 50 to 55 psi /345-379 kPa |
| 1100F/430C | Between 50 to 55 psi /345-379 kPa |
Faults in the Air Conditioner and their Possible Solutions
When the low-pressure reading is in the normal range, it means that the AC is working properly, and there is no need for you to worry about repairing the system. However, when the blue gauge readings are low, then the AC is pumping too little of the refrigerant through the system, and you need to add more refrigerant (if the AC system is manually operated). On the other hand, if the system in your car is automatic, there is no need to worry because the AC will regulate the system’s amount of refrigerant.
When the pressure reading is too high in the low-pressure system, there is a variety of causes for the problem. This issue could indicate that the AC compressor is worn out and requires service. It could also mean that the system has overcharged, and the possible solution to this problem is to slowly remove the refrigerant from the system.
It is advisable that when the car’s interior is at an undesirable temperature, the AC should be turned on, vacuumed for not less than 15 minutes, then charged until it is full. When the system is turned off, the pressure will be minimal on a cold day, and hot outside temperatures will increase the pressure. This phenomenon arises from the gas laws, which govern the relationship between gaseous temperature and pressure. When the pressure increases, the temperatures could also rise to the point of blocking the pipes and the filters. Near-freezing temperatures can immediately follow this malfunction.
Other times, when the AC’s compressor has lost its tolerance, the system will be unable to build up sufficient suction on the inlet. Therefore, the readings on the blue gauge will be too high.
Recharging the r134 Air Conditioning System
Most times, the air conditioner loses its ability to reduce the temperatures in the car. The best course of action, in this case, is to recharge the AC with a fresh refrigerant (usually the r134), especially if your car has been using the outdated R12. The vehicle’s pressure should be low, or the car AC has been vacuumed after servicing the compressor.
The first step is to purchase the CA pro r134a recharge kit from an authorized car spare parts dealer. Since this is a do-it-yourself procedure, you should wear safety goggles and other protective gear. It is worth noting that most refrigerants are highly flammable and should be handled with utmost care. Therefore, the process should operate at low temperatures and pressure to reduce the risk of a fire.
1: Determine the Ambient Temperature
When recharging the AC using virgin refrigerants, the air temperature inside the vehicle should be below 550F. Most experts recommend that you should recharge the system using a temperature. Also, you should the chart outlined above to determine the right temperature and pressure for the process. Usually, there is a similar chart contained in the refrigerant packaging. Not only will using this chart ensure that the process is safe for you, but it will also ensure that the AC system is functioning efficiently after the recharge.
2: Find the Low-Side Service Port
In most cars, the port used to recharge the AC system is located in the conduit between the compressor and the system’s accumulator. Look carefully between the condenser and the accumulator to find the port. However, if you cannot find it, and you do not want to hire an expert for the process, then you should consult the service manual to locate the port. If the car is a 1994 or older model, it probably uses the R12 as the refrigerant. This Freon has been banned for over two centuries and should not be mixed with any other refrigerant. Therefore, during this step, evacuate the Freon because this will make the process significantly more dangerous.
3: Clean the Port and the Most Important Parts of the AC
Before detaching the cap from the low side pressure service port, it is standard practice to clean the area using a clean rag. However, the rag to be used to clean the area should not be wet. This is because the freon should not mix with any other fluid. Once all the dust has been wiped off the area, then you should proceed to the second step.
4: Connect the Charging Hose to the Port
This step involves attaching the hose to the low-pressure service port of the air conditioner. You should ensure that the connection is secure since any leaks are dangerous. However, if the hose does not attach easily, it indicates that you may be attaching it to the wrong port. Therefore, you should consult the service manual to locate the correct one or enlist a mechanic’s services.
5: Add the Refrigerant
If you are conversant with the process of recharging the system, then go ahead and complete the process. Nonetheless, it is advisable to follow the instructions on the user manual of the Freon. Using the service manual ensures that the process is safe and that the AC will operate normally after the refrigerant has been added to the system.
6: Charge the System
Step six is the most crucial in the entire process. Determine the right conditions of pressure and temperature from the chart provided. You should monitor the pressure level during the entire process of recharging the system. Use the gauges to determine the pressure levels since charging the system involves building up pressure to the appropriate levels. This process takes about 20 minutes for most modern cars. However, keep a keen eye on the process and ensure your system is fully charged.
7: Detach the Charging Hose
After the pressure reaches the optimum level, disconnect the charging hose, since it means that the AC compressor is fully charged. Leave the can of the r134 freon attached to the hose and store any remaining refrigerant in dry, cool storage space. Ensure that the liquid does not leak since the Freon is flammable. Be very careful when executing this process and handling the refrigerant.
8: Examine the Cap Seal Before Reattaching It
It is important to check whether the cap has any cracks and other signs of wear and tear. This action prevents any Freon from leaking from the service port. If any are found, purchase a replacement seal to restore the functionality of the system. After this process, the AC’s recharge is complete, and the change of functionality will be noticeable immediately. However, the pressure should constantly be monitored for any leaks that may have been overlooked. Some holes in the system might be too tiny to be perceived by inspecting the system and its conduits. However, you can circumvent this shortcoming by using either a UV light and UV dye. Applying the dye will ensure that you can find the leak by shining the light over the AC system’s components.
However, it is important to note that replacing the R12 freon with the R134a one will make your car’s AC system to be less effective than before. This is because the R12 system was not designed to use any other refrigerant other than R12. This is disheartening for people who love antique cars. Additionally, you may use a little of the refrigerant that was sucked out of the system before the recharge process. Some cars may also require new condensers and compressors since the newer Freon might not work well in the old system. However, it is much easier to shop for the R134a than the R2, since the latter has been banned in many countries.
You Need to Know This About Your AC
Failing to maintain your AC can result in the AC failing and having problems. You need to make sure that the components that allow the AC to function are being looked after unless they can start to fail overtime. This can cost a lot to repair so it’s best that you prevent this from happening.
If you want to avoid AC problems or other issues and save $100s of dollars that you’ll spend at the auto repair shop, you’ll need to service your vehicle often – you can use our mechanic-rated Auto Maintenance and Repair Manual to do this. It’s basically what mechanics use to go through your vehicle to check if there are any problems that need fixing. As soon as they notice the most minor problem, they’ll ask you to fork out some money even though it’s a problem you can fix yourself in minutes – the manual will teach you how to maintain your vehicle every few thousand miles and it’ll teach you how to fix minor problems that mechanics will ask you to pay for; saving you money in the long run.
A lot of our readers have the Auto Maintenance and Repair Manual printed on their garage wall and 92% of them haven’t visited the auto repair shop in the last year because they know what to do to avoid problems. All it takes is giving your vehicle a little attention every few thousand miles and you’ll never spend money at the workshop again.