Dometic 4450037544 PTCR Relay for FreshJet 5 AC

When a Dometic FreshJet 5 blows air but never gets cold on a hot afternoon, the problem is often the little component the compressor leans on to start. That's the PTCR relay. This is the genuine Dometic 4450037544, the positive temperature coefficient start device that gives the compressor its surge of current at startup, then backs off once the motor is spinning. It's a small part with an outsized job.

Here's what's happening inside your rooftop unit. Every time the thermostat calls for cooling, the compressor motor has to break free from a standstill against the pressure sitting in the refrigerant loop. That takes a big jolt of current for a fraction of a second. The PTCR relay routes that jolt to the start winding, then drops it out of the circuit once the motor is up to speed. When the relay ages out, the compressor can't get over that first hump. You'll hear it try. A hum, maybe a click, and then nothing. The fan keeps running and the air coming out of the ceiling assembly stays room temperature.

Those are the classic signs a PTCR relay has failed. The AC hums but the compressor won't kick in. It trips the breaker a second or two after it tries to start. Or it cools fine on a cool morning and quits on you once the rooftop bakes in the afternoon sun. Before you write off the whole air conditioner, this relay is one of the cheapest and most common things to check. A lot of dead FreshJet 5 units come right back to life with a fresh one.

This is the real Dometic part, not a generic stand-in. Ordering the OEM 4450037544 means the relay matches the compressor and control board your FreshJet 5 was built with, so you're not guessing at ratings or splicing in something that almost fits. The UPC is 7333497000295 if you want to cross-check before you buy.

Fitment covers the FreshJet 5 family broadly. It fits FJX5357MHEBKCS, FJX5357MHEWHCS, FJX5457MBKCS, FJX5457MWHCS, FJX5557EHPBKCS, FJX5557EHPWHCS, FJX5557MBKCS, FJX5557MHPBKCS, FJX5557MHPWHCS, and FJX5557MWHCS. That spans the cool-only units and the heat pump versions, and both the black and white finishes. The FreshJet 5 is Dometic's low-profile rooftop AC, the one a lot of owners put on as a direct Penguin II replacement, so this relay covers a huge slice of the coaches on the road today.

Replacing it is a job a handy owner can take on, but respect the power. Kill the shore power and the breaker before you touch anything. The relay lives in the control box up on the roof, under the shroud, so you'll be working on top of the coach or at the ceiling assembly depending on your model. If you're not comfortable pulling the shroud and identifying the relay on the control board, this is a quick job for any RV tech. Either way, the part itself is the easy part once you're in there.

A quick word on what this is and isn't. This is the start relay, not the run capacitor, not the thermostat, and not the main control board. If your compressor is truly seized or the sealed system has lost its charge, a new relay won't bring it back. But when the symptom is a compressor that strains to start, hums, or trips the breaker on startup, the PTCR relay is the first and cheapest suspect, and swapping it is a whole lot easier on the wallet than a new rooftop unit.

Keep one on the shelf if you full-time or travel through hot country. It's a small, inexpensive part that tends to fail at the worst possible time, the middle of a heat wave when you need the AC most. Having the genuine Dometic relay on hand is the difference between a ten-minute fix and a night sweating it out waiting on parts.