[Solved] Dometic Fresh Jet not cooling

Here is the context of what has happened to get to this point.

I was at the point where the unit was going to cost $800 to repair, and a new system is $2000. So I figured I would give a re-gass a try.

Disclaimer: This is a record of my experience only. Handling refrigerants is potentially dangerous and in many places it must legally be done by a licensed technician. This post is for educational purposes — proceed at your own risk.

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The Gear I Used

• Piercing valve
• Errecom Ultra HVAC sealant
• Gauge set
• HC-32 (hydrocarbon refrigerant, propane/isobutane blend)
• Vacuum pump
• Ladder

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Step 1: Vacuuming the System

I first hooked up the vacuum pump and pulled the system down for about 20 minutes.

• The goal here is to remove any moisture or non-condensable gases from the lines.
• After switching off the pump, I left the gauges on to see if the vacuum held.

👉 Good sign: The system held vacuum! That means there were no major leaks.

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Step 2: Sealant (Optional)

Even though the system held vacuum, I installed Errecom Ultra sealant.

• This is an additive that circulates with the refrigerant and seals micro-leaks if they develop.
• It’s debated in the HVAC community, but I figured it couldn’t hurt.

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Step 3: Charging with HC-32

Here’s the critical part: getting the charge amount right.

• My system was originally designed for R32 with a factory charge of 500 g.
• Rule of thumb: HC-32 only needs about 40% of that weight → ~200 g.
• In practice, my system ran properly at closer to 300 g.

This shows that weight alone is not enough — you need to check superheat.

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Step 4: Understanding Superheat

Superheat = (suction line temperature) − (saturation temperature at suction pressure).

1. Hook gauges up to the low side.
   • Example: ~100 psi suction pressure = 8 °C sat temp (for HC-32).
2. Measure the actual pipe temperature with a clamp probe.
   • Example: suction line = 18 °C.
3. Subtract → 18 − 8 = 10 K superheat.

👉 A good target is 5–10 K.
This ensures the refrigerant is fully vaporized before it reaches the compressor (no slugging risk).

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Step 5: What the Numbers Mean

Here’s a quick reference for HC-32 low-side saturation temps:

Low-Side Pressure (psi)	Sat Temp (°C)	Sat Temp (°F)
40	−14	7
50	−10	14
60	−7	19
70	−3	27
80	3	38
90	8	47
100	12	54
110	15	59
120	20	68
130	23	73

I got some good results, with the system now cooling nicely!

Terms Explained

1. Superheat

• The difference between the actual temperature of the suction line and the saturation temperature at that pressure.
• Ensures the refrigerant is fully vaporized before entering the compressor, preventing liquid slugging.

2. Saturation Temperature (Sat Temp)

• The temperature at which refrigerant boils (evaporates) at a given pressure.
• Found from a pressure-temperature chart for the specific refrigerant.

3. Low Side / High Side

• Low side: suction line from the evaporator to the compressor (low pressure).
• High side: discharge line from the compressor to the condenser (high pressure).

4. Critical Temperature

• The maximum temperature at which a refrigerant can exist as a liquid.
• Above this temperature, the refrigerant cannot condense, no matter how high the pressure.

5. Vacuuming the System

• Using a vacuum pump to remove air, moisture, and non-condensable gases from the system before charging.
• Critical for proper cooling and preventing corrosion or ice formation.

6. Refrigerant Charge

• The amount of refrigerant in the system.
• Measured in grams or ounces. Too much or too little can affect performance and compressor safety.

7. HC-32

• A hydrocarbon refrigerant (propane/isobutane blend) often used as a drop-in replacement for R32.
• Lower density and higher latent heat than R32, meaning less mass is needed for the same cooling.

8. Errecom Ultra Sealant

• An additive that circulates with the refrigerant and seals small leaks.
• Optional, but some DIYers use it as an extra precaution.

9. Slugging

• When liquid refrigerant enters the compressor.
• Very dangerous for the compressor because it is designed to compress vapor, not liquid.

10. PSI

• Pounds per square inch, a unit of pressure.
• Used to measure the low and high side pressures in the system.

11. Temperature Clamp / Thermometer

• A device used to measure the actual temperature of the suction line or other parts of the system.