What You Need to Know Before Starting

Replacing AC coolant (also called refrigerant) in a 2015 Ram truck is a job that requires specialized equipment and knowledge of your truck's specific AC system. Your 2015 Ram uses R-134a refrigerant, which is the standard for vehicles made after 1994. The process involves evacuating the old refrigerant, replacing the oil in the compressor, and recharging the system to the correct pressure — all of which requires a refrigerant recovery machine and a manifold gauge set that most home garages do not have.

This is one of the few truck maintenance tasks where a DIY approach often costs more in equipment rental than a shop visit would cost. If you do decide to proceed, understand that venting refrigerant into the air is illegal under the Clean Air Act, and the recovery machine is not optional. You will also need to know your truck's exact coolant capacity and the correct high-side and low-side pressures for your specific Ram model and engine size.

Key Takeaways

  • A 2015 Ram truck uses R-134a refrigerant, and you must use a refrigerant recovery machine to remove the old coolant — venting it is illegal.
  • The job requires a manifold gauge set, a vacuum pump, and a refrigerant scale to measure the charge accurately, which most home mechanics do not own.
  • Your truck's AC capacity and correct pressure readings are printed on a label under the hood; write these down before you start.
  • If the system has been open to air for more than 15 minutes, you must replace the receiver-drier and add fresh compressor oil to prevent moisture damage.
  • Most shops charge $150 to $300 for a full recharge, which is often less than renting the equipment and buying refrigerant yourself.

Locate the AC Service Ports and Capacity Label

Open your truck's hood and look on the driver's side of the engine bay, near the firewall. You will see two metal ports on the AC lines — one smaller port (low-side) and one larger port (high-side). The low-side port is usually on the larger aluminum line coming from the compressor; the high-side port is on the smaller line. Do not confuse these — connecting gauges to the wrong port can damage your manifold set.

Next to or near the compressor, you will find a white or yellow label that lists your truck's AC system capacity in ounces and the correct operating pressures. Write down both numbers. For most 2015 Ram trucks with standard AC, the capacity is between 32 and 40 ounces, but this varies by engine and whether your truck has dual-zone climate control. The label also shows the type of oil your compressor uses — usually PAG 46 or PAG 100. This matters because using the wrong oil can damage the compressor seals.

Gather Equipment and Refrigerant

You will need a refrigerant recovery machine (not optional — this is the law), a manifold gauge set rated for R-134a, a vacuum pump, a refrigerant scale that reads in ounces, fresh R-134a refrigerant in the correct quantity, and the correct compressor oil for your truck. You will also need a receiver-drier cartridge if the system has been open to air for more than 15 minutes, because moisture will have entered the lines and will damage the compressor.

Refrigerant recovery machines can be rented from most tool rental shops for $40 to $80 per day. A basic manifold gauge set costs $30 to $60 if you buy one, or you can rent one for $15 to $25 per day. A vacuum pump rental runs $20 to $40 per day. A refrigerant scale costs $25 to $50 to buy. R-134a refrigerant costs $5 to $8 per pound (12 ounces), so a full charge will cost $15 to $30. A receiver-drier costs $20 to $50. Add these up, and equipment rental alone often exceeds what a shop would charge.

Evacuate the Old Refrigerant

Connect the recovery machine to both the high-side and low-side ports using the hoses that came with the machine. Follow the machine's instructions — most require you to flip a switch and let the machine run until the pressure gauges on both sides read zero. This step removes all the old refrigerant and any moisture in the system. Do not skip this or rush it; the machine needs 15 to 30 minutes to fully evacuate the system depending on how much refrigerant is left.

Once the gauges read zero on both sides, close the isolation valves on the recovery machine and disconnect the hoses. The old refrigerant is now safely stored in the machine's tank and can be recycled at a shop or disposal facility. If you rented the machine, the rental shop will handle disposal when you return it.

Replace the Receiver-Drier and Add Compressor Oil

If your system was open to air for more than 15 minutes, you must replace the receiver-drier. This is a cylindrical component that removes moisture from the refrigerant. Moisture in the system will freeze at the expansion valve and block coolant flow, or it will mix with refrigerant to form acids that corrode the compressor. The receiver-drier is usually located near the condenser on the passenger side of the engine bay.

Disconnect the two refrigerant lines from the receiver-drier using a wrench — expect a small amount of oil to drip out. Remove the mounting bolt and slide the old unit out. Before installing the new receiver-drier, add the correct amount of fresh compressor oil to the new unit. Your truck's label will tell you whether to use PAG 46 or PAG 100 oil, and how much — usually 1 to 2 ounces. Install the new receiver-drier, reconnect the lines, and tighten them firmly but do not over-tighten.

Vacuum and Recharge the System

Connect the vacuum pump to both the high-side and low-side ports using the manifold gauge set. Turn on the pump and let it run for at least 30 minutes. The gauges should drop to 0 to 2 inches of mercury (or below 5 millibars on a digital gauge). If the pressure does not drop below 5 millibars, you have a leak in the system and should stop — a leak will prevent the new refrigerant from staying in the truck.

Once the vacuum is complete, close the isolation valves on the manifold set and turn off the pump. Now you are ready to add refrigerant. Place a can of R-134a on the refrigerant scale and zero the scale. Connect the can to the low-side port using the hose on the manifold set. Open the valve slowly and let refrigerant flow into the truck until the scale shows you have added the correct amount from your label — for example, if the label says 36 ounces, add exactly 36 ounces. Close the valve and disconnect the can.

Start the truck and turn the AC to maximum cooling. Watch the manifold gauges. The low-side pressure should be between 25 and 35 psi, and the high-side pressure should be between 200 and 250 psi, depending on the outside air temperature and your truck's label. If pressures are too high or too low, you may have added too much or too little refrigerant — turn off the AC and adjust by adding or removing small amounts. Once pressures are correct, close all isolation valves, disconnect the gauges, and cap the service ports.

Check for Leaks and Test the System

Run the AC for 10 to 15 minutes and feel the air coming from the vents. It should be noticeably cold — around 40 to 50 degrees Fahrenheit at the vent. If the air is warm or only slightly cool, the system may still have a leak or you may have undercharged it. Turn off the AC and let the truck sit for 5 minutes, then check the manifold gauges again. If the low-side pressure drops more than 5 psi while the truck is off, you have a leak.

A leak means refrigerant is escaping and the system will not hold a charge. Common leak points are the compressor shaft seal, the hose connections, and the condenser. Finding and fixing a leak requires a leak detector (electronic or dye-based) and often requires replacing a component. This is the point where most DIY jobs turn into shop visits — if you find a leak, disconnect your gauges, cap the ports, and take the truck to a shop.

Frequently Asked Questions

Can I recharge my AC without evacuating the old refrigerant first?

No. Mixing old and new refrigerant, or adding new refrigerant to a system that still contains the old type, can damage the compressor and create pressure imbalances that cause the AC to fail. Evacuation is not optional — it is the first step.

What if I do not know whether my truck has a leak?

If the system held pressure during your vacuum step (pressure stayed below 5 millibars for 30 minutes), you likely do not have a major leak. Minor leaks may show up over weeks or months as the charge slowly drops. If the AC cools well when ready after recharge but stops cooling within a few weeks, have a shop check for leaks with a leak detector.

Do I have to replace the receiver-drier every time I recharge?

Only if the system was open to air for more than 15 minutes. If you are topping off a system that has been sealed, you do not need to replace it. If you are doing a full evacuation and recharge, replacing it is cheap insurance against moisture damage.

What is the difference between the high-side and low-side ports?

The low-side port connects to the suction line from the evaporator and has lower pressure (25 to 35 psi when running). The high-side port connects to the discharge line from the compressor and has higher pressure (200 to 250 psi when running). Always connect the correct hose to the correct port — the manifold set is designed to prevent cross-connection, but mistakes can damage the gauges.

Why is this job so expensive to do at home?

The refrigerant recovery machine is the main cost. It is specialized equipment that most home mechanics do not own, and renting one for a day costs $40 to $80. Add in the manifold set, vacuum pump, scale, and refrigerant, and you are at $150 to $200 in equipment and supplies. A shop charges $150 to $300 total and has the equipment already, so the math often favors the shop.