How to diagnose HVAC issue?

R

Robillard

New Member
Jun 22, 2012
43
Santa Cruz, CA
Boat Info
330 Sundancer 1998
Engines
Twin 454 Mercruisers, V-drives
The A/C and heater on our 1998 330 DA seems to only work occasionally. I've had it work just fine, but rarely. Most of the time, it seems to just endlessly power-cycle. I can hear the main A/C unit switch on and start to do something, and then just switch off. This continues, about every 15 seconds or so (I'll actually time it later today).

Any idea what could cause this, or how to go about diagnosing it? I'm pretty new to HVAC systems, so really, don't know where to begin...

Thanks in advance...
 
quick cycling usually indicates low refrigerant levels
probably needs a recharge
 
This is something that should be checked by a trained qualified a/c tech. Sorry.

I spent 30 years in the business. But generally speaking ..it's pretty hard to troubleshoot and diagnose a/c problems over the net like this.

I presume by your statement...." it seems to just endlessly power-cycle. I can hear the main A/C unit switch on and start to do something, and then just switch off. This continues, about every 15 seconds or so "........your compressor is short cycling.

This could be an electrical issue....or a refrigerant pressure issue.

I'd suggest you bite the bullet and get a tech to check it.
 
Sorry, should have been more specific... The same happens with the heater (when it's cold) as with the A/C (when it's hot). Does that rule out refrigerant pressure?

I'd love to hire a professional, just no idea how to find a marine HVAC tech in my area. I'm new to harbor boating, so I'm not sure how to get good local recommendations. I suppose I could ask the harbormaster?
 
if it's the same with the heat ...probably an electrical issue
agreed...find a HVAC tech and get it right the first time.
 
If your system has crusair control panel (smxll) look at the troubleshooting guide. There are a couple simple checks you can make. It cites a flow restriction as a possible cause for compressor cycling. Probably worth checking strainers. The panels can also get flaky, so try a reset. if you have 2 panels, try swapping them. if it ends up being a panel they can be repaired for about $100. New ones around $240.

Here's the guide if you have a smxll.
http://www.dometic.com/d61bdad1-3331-4d66-ba27-8843b76e4b81.fodoc
 
searay40dad said:
If your system has crusair control panel (smxll) look at the troubleshooting guide. There are a couple simple checks you can make. It cites a flow restriction as a possible cause for compressor cycling. Probably worth checking strainers. The panels can also get flaky, so try a reset. if you have 2 panels, try swapping them. if it ends up being a panel they can be repaired for about $100. New ones around $240.

Here's the guide if you have a smxll.
http://www.dometic.com/d61bdad1-3331-4d66-ba27-8843b76e4b81.fodoc
Click to expand...

Excellent, thanks for the link! I'll play around with it this weekend, and if I cannot make heads or tails of it, then I'll pull in an expert.
 
Do you have refrigerant gauges? Very helpful to have details as to what the pressure readings are under cooling/heating cycles. After ruling out any basic electrical issues or with the remote panel, investigation should focus on the pressure within the system. If you are low on refrigerant, it may be a result of a slow leak on a fitting so adding refrigerant might only be a short-term fix. Might want to ask around and see if you can get a boat hvac tech to take a look at it before you waste time and money. The other option is just replace the unit with a new one. 15 years old...might be worth looking into as the new units are more efficient, environmentally friendly and quieter. You can get them for a little over $1000 on ebay.
 
I agree with hiring a tech as others advised but if you plan trying it alone first,
try one of these,sized to your compressor HP or BTU. About $12 to $20

​
Relay,Overload and Hard Start Capacitor
Item # 4LWX4
Hard Start, Relay, Overload and Start Capacitor, Control Volts 115, Voltage 115, Phase 1, 1/3 to 1/2 HP
 
Sound like the temperature limit switch which is on top of the compressor. Next chance you get, see if the to of the compressor is red hot when it kicks off...

Multipe reasons can cause this situation, but will need a tech to get you back in shape anyway...
 
This is an area I know something about and I agree with the replies you are getting. The only thing I want to add is you don't need a "marine" hvac tech. Any hvac tech could diagnose this for you, a commercial tech familiar with WSHP (water source heat pumps) would be better. Find one willing to put an eye on it "after hours", probably looking at a 2 beer charge for him to tell you what's wrong, then you could go from there. I would do it for you but the travel time would be a killer.
 
Interesting, good to know I may not need a dedicated marine HVAC person, as I'm having a helluva time finding one. Xravenx, consider flying out for a case of beer? Two? I promise not to wear any 49ers gear, or mention the super bowl... (*grin*) Seriously, though, thanks for the advice, you've likely saved me some serious dough, and I very much appreciate that.

I spent some time on the boat trying to figure out what's going on yesterday, and here are some further notes:
- water flow through the system seems fine, it's spitting out the thru-hull a steady full stream, which indicates to me that the intake is also fine
- I can hear what sounds like the compressor engaging, and it stays engaged for about a minute, maybe, and then shuts down
- a control panel reset did not help (Cruisair SMX II)
- no error codes are displayed on the control panel
- the control panel itself does not cycle, just the compressor
- the fan never comes on
- the fan doesn't even come on when I manually engage it

These latter two points suggest to me that either I have two separate problems, or that the fan itself is the problem, and the compressor is shutting off because the fan is not coming on.

I'm going to poke around a bit more, but I suspect that I will end up having to pull someone in.

Thanks again, folks, great to have this resource of helpful people!
 
you don't need a "marine" hvac tech. Any hvac tech could diagnose this for you, a commercial tech familiar with WSHP (water source heat pumps) would be better.

And I agree whole heartedly. An a/c system is an a/c system...be it in your house or in your boat. Any good tech should be able to troubleshoot it and diagnose your problem.

I would do it for you but the travel time would be a killer.

As would I if you were in my club.....a couple cold beer would suffice. :)

Good luck.
 
Although I'm far from an hvac expert, I have heard of a lot of problems with crusair systems over the years and I'd bet 75% or more ended up being electronic in nature. This link describes some common problems and is a good resource if you end up needing to repair or replace a logic board. I'm betting it's electronic, and probably the control board on the compressor. Read the troubleshooting link in the link below.

http://www.flightsystems.com/generator-ats-controls/cruisair-smx-rebuilding-service.htm
 
rob,

The fan not coming on is a problem, and may be the only problem, start there. Searaydad is on the right track about the electronics, something tells the fan to run, this has nothing to do with the refrigerant charge.

BTW................you can mention the 9ers, Ravens, Super Bowl, etc. in the same sentence anytime you want.

John
 
never worked on these particular a/c systems so I'm not fully aware of all the components in one but.....

I'm wondering if there is a low pressure cut out switch....and if the fans not running......a low pressure condition is being created?

I'd also make every effort to get that fan running before going further.
 
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