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Marine AC

joeg

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"Gentlemen,

Perhaps you


"Gentlemen,

Perhaps you can help me with a marine HVAC problem that I am having with my 1985 Carver 32 Aft Cabin. The vessel has a 16,000 BTU Marine Air Systems (now Dometic) HVAC unit (actually two units tied together, one in the salon and one in the aft cabin). They share a common water pump and a common electrical relay box with two relays. The HVAC unit model number is RRK4-0126-PAA, and each of the relay model numbers are 240A25.

Both units cooled perfectly last summer and heated adequately this winter, but this spring they quit (and popped the circuit breakers) due to a siezed water circulation pump. I replaced the pump with an exact replica which pumps well. When I tried to restart the HVAC units, the Aft Cabin unit ran fine however the Salon unit fan ran properly but the compressor engages and immediately disengages after less than 2 seconds. When this happens the ampmeter swings wildly. It will "hit" on and off a few times and eventually pop the breaker. The boat is tied to shore power via 2 30A cables plugged into a 50A Y at the pole (a common setup) and while doing routine maintenance the other day I noticed that one of the cable plug terminals (that feeds the panel containing the HVAC breakers)was fried. I thought that this bad cable may have been the problem with the HVAC but now I think that the HVAC may have caused the cable to fry. I replaced the cable and still had the same problem with the unit.

My suspicion is that the relay is the problem. Are there any tests that I can possibly use to tell if that is the case? Any other ideas?? I have attached a photo of the electrical box wiring diagram that houses both relays. Unfortunately the budget will not accomodate a service charge from the marine HVAC man and any help would be much appreciated. It's going to get mighty hot here in South Carolina very soon!!

Sincerely,

Joe"
 
You need to place a amp meter

You need to place a amp meter on the compressor and check out the amps being pulled at time of failure. It is possible the compressor was damaged by an over heat condition when the circ pump failed. You should of had a over temp switch trip when the pump failed.
 
It is either a compressor or a

It is either a compressor or a capacitor. Swap the capacitor from the other unit and see what happens. If it still doesn't work you're screwed.
 
"When a relay goes bad there i

"When a relay goes bad there is usually a noticeable burnt spot on it.there is usually a schematic of the pin routing on top of the relay. I would check for loose/corroded connections,especially the main 120vac black and white wires going to the main unit lugs, also check for fuses protecting the control circuits on the unit itself.I would also check the black ac power wire going into the breaker panel to see if its loose or corroded.If all that is OK, then I agree with the other 2 men, capacitor or compressor. They probably know better than me because I'm not an AC guy, I'm an electrician."
 
"The clamp on AC amp meters ar

"The clamp on AC amp meters are the easiest to use. The compressor should have its current draw on a plate or decal (sometimes you can find it in the manual). You may be able to rent the amp meter from a tool rental shop if you can't buy one.

The run capacitors don't like surges. If it is distorted (connector end bulged out), I'd start with it.

Another option is a "hard start kit" which isn't a bad addition to one running fine...In essense, it is a starting cap that switches itself out once the compressor gets going."
 
"makomark:
what is a hard sta


"makomark:
what is a hard start kit? always interested in learning something, I have seen on single phase units the second capacitor, but how does that work?
thanks."
 
"GL: It is a starting capacito

"GL: It is a starting capacitor with a voltage sensitive relay (or cheaper "functional equivalents") that goes in the comressor power line. I'd suggest www searching on "hard start kit" to get the details on operation and implementation. I use the kick start brand - {www.kickstartoem.com}. Scott's site also have a lot of material on AC troubleshooting: http://toad.net/~jsmeenen/boom.html"
 
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