advice about AC problems

[Jolly Roger]

I have two Pompanette Air 16,000 btu AC units on my boat, which have worked very well for five years in Florida heat. Now, one has refused to blow cold air and the manufacturers have not been very helpful to troubleshoot the problem.
The fan still works fine, but the compressor is not coming on at all.
The other unit works great and I wondered if I could change the compressor capacitor from the working unit, to see if that makes it work.
I would really appreciate any ideas what might be the problem, to save me calling out a AC engineer at umpteen dollars per hour.
It’s starting to get hot down hear now.

[donradcliffe]

The first thing the AC guy will do is blow out the cooling water lines and make sure you have good flow through them. Something you could do yourself.

[Jolly Roger]

The flow seems just like it always is. I have an outlet from each unit from the common pump and water is flowing out of the forward and rearward unit like normal. I will flush them out though, just to be sure.
Thanks

[a64pilot]

Often when the compressor doesn't come on, it's the thermostat.
You sure the compressor isn't running, that would be where I would look first.

[Jolly Roger]

Nope! Good thought, but I changed out the control button for the good unit and it made not difference.

[Maker42]

Yes, if the fan is blowing but the compressor motor is not running, it is the run capacitor that is usually the problem. If you have 2 identical units, swapping in the capacitor from the working one will help identify the problem.

In more rare circumstances, the logic board might be the problem. That might be round 2 if the capacitor is eliminated.

[jmac9365]

Did you put a set of gauges on it to make sure you have adequate freon

[Sailmonkey]

Originally Posted by jmac9365

Did you put a set of gauges on it to make sure you have adequate freon

If the compressor won't come on at all, or even try to start, there's a good chance this is the culprit. These things almost always have a high and low pressure switch to interrupt the compressor current. Low or no Refrigerant will cause this. If the water flow is too low, the unit will blow cold for a short time until it trips off under a high pressure fault.

[redsky49]

Originally Posted by jmac9365

Did you put a set of gauges on it to make sure you have adequate freon

If the compressor does not start at all, and the unit had worked properly before, I would not start fooling around with the refrigerant.

Start with the basics: Is the unit receiving a signal to start the compressor?

Trouble shooting refrigeration equipment starts with a logical plan. Could be a wiring issue, for example. After five years, corrosion on a terminal could have occurred.

Assume nothing. Check everything. And like Mr. Holmes, "Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth."

Good luck!

[Jolly Roger]

Thanks Guys,
The manufacturer told me not to switch the capacitors because of the high current, (they would though, wouldn’t they?). If both units have been off for an hour, is there any current still in a capacitor anyway?
One of the problems with the freon is it is a number I’ve never heard off. Pre R22 I think, and the factory can’t fill it up anyway. So I want to leave that one alone as a last resort only.
I’m thinking of taking the whole thing it out to give it a good clean, then I can check for bad wiring, dirt in the radiator, etc. Trouble is it weighs 80 lbs and high up in a locker.
JR

[pesarsten]

Don't start messing with the refrigerant charge before everything else is checked. And don't worry so much about old refrigerant types. All are still available even R22, but at a premium cost. If someone tells you you have to replace because of the refrigerant type, get another opinion. Do you know what's in yours? Likely 134 or 410 .
Yes the cap will store energy for a loooooong time, breakers off, then short the terminals using a WELL insulated screwdriver. Or better yet, find the values and get a replacement from any hvac supply house, they're cheap! If you can't find the values test with 35 mf 370 v. It also can be a high or low pressure cutout switch or the compressor delay switch or even the compressor itself. Check to see if the compressor gets very warm when it has been on for 30 min.

[Jolly Roger]

Thanks Pesarsten.
I can't do the feon anyway, don't have the gages. I can't remember what the number is, but it's on the lable. I'll know tomorrow.
I'm going to the boat tomorrow and the AC's will have been off for three days. Surely the capacitor won't still be live will it. I could take the faulty unit capacitor to a HVAX place and maybe they could test it for me??

[GregW1309]

Until you discharge it, count on the capacitor being charged!!!

[redsky49]

Caps can and will fail over time. Five years is not too soon if HVAC unit used extensively, though that would not be the first thing I would consider. Do you know how to identify a capacitor? If soldered to a board, will you be able to safely unsolder and replace without damaging adjacent components or the board? A badly damaged cap may be visibly distorted. They sometimes swell or leak. Not sure what you are looking at with your installation.

Again, start with a plan. I would confirm voltages first thing. So many times, problems on a boat are due to electrical issues. Could be as simple as low voltage or loose connection.

Do you have a good multimeter and test probes? A VOM is your friend in cases like this.

A quick check of refrigerant lines for evidence of leaks takes no special tools. Oily connections or discolorations, though you will have to look closely, frequently appear if refrigerant and associated lubricant are escaping.

Can you hear the relay actuate when you index the t'stat to cooling?

Not sure what your knowledge/comfort level is, so I am suggesting some simple steps to pursue first.

[Jolly Roger]

Thanks Redsky49. I'm fairly good with electronics and I know how a AC works. I'm going to take it out of its locker and give it a good inspection and clean. I've got a good multimeter as well. I thought the capacitor was the big round ally thing strapped inside the control box. I'll be back when I get it out tomorrow.
JR