Two Identical Dometic Turbo DTU Units Performing Differently

[Howler]

We have two Dometic Turbo DTU AC/Heat Pump units onboard... one for forward cabin and salon, the other for aft cabin and head.

• We've been running them in heat (reverse cycle) mode.
• Ambient air and water temperature are in the 50ºs F.
• Thermostats are set identically at 68º F.
• Both have good water flow, etc.

However, one unit is pumping out air at around 78º shortly after starting, and heats the cabin to desired temperature in several minutes. The other unit only pumps out air at around 64º and never really gets the cabin to target temperature.

Any suggestions as to why the two would behave so differently and, more importantly, why we can't get sufficient heat out of one of them? Thanks.

[Mike32]

Based on my experience with my 3 Dometic DTU’s, I would say that it’s because the coolant has leaked out. I’ve had 2 of the three units replaced completely under warranty and now that the warranty is up, one of those and the other one have coolant leaks. I’m ready to switch brands.

[Turtle Blues]

Need to know refrigerant pressures as first step. Fortunately you have 2 side by side to directly compare. After that cycle times, amp draw, return air etc. The 28' bump sounds normal. The other one is definitely sub-performing.

[Howler]

Epilogue - Underperforming unit needed refrigerant recharge. Couldn’t detect slow leak. We’ll see how long it lasts.

By the way, I learned that these units use the same recharge equipment and product as home AC units. I had our home HVAC service company do it rather than pay 3X for a “marine” AC company. It was hist first boat so I felt bad he had to crawl around in tight spaces. He said he’d been in tighter spaces in houses with dirt floors, dead bugs and worse. So I guess crawling around in a boat isn’t so bad after all :-).

[Mike32]

I think I’ve seen this movie before.

I’ve been down this rout twice so far. “There’s a leak but it must be small and we can’t find it.” So, you recharge it and see how long it lasts. The answer is - a few months and then it’s back to room temperature air blowing around.

Right now I’m shopping for a new brand. I’ve got two to replace - an 8’000 and a 12’000 btu unit. i might up the capacity to 10 and 16 because - why not? The price difference isn’t a lot either. I was looking at Webasto but the form factor might not work. They’re more square in shape and bigger and heavier overall than the OEM Dometic. Now I’m looking at CTM’s. They’re pricier though but they’re a US company.

Good luck with your fix. Hope it works for you.

[Turtle Blues]

Yup,Off brand gauge set probably $35. Small can of refrigerant about the same. Can be purchased with leak detector but don't recommend unless chronic problem. Schrader valves and other mechanical connections are the first suspect. Little soap and water with a spray bottle is the easiest check.