advice about AC problems

[dtrue]

There is a quick way to check capacitor, by installing a hard start kit across run capacitor. You can diy
Checking compressor, better call tech.

[dtrue]

Jolly the run cap is usually rectangular and the start cap almost always round.
Testing in ohms, charge one side and reverse leads while watching for discharge on multimeter. Same the otherside first but hard to check actual discharge with most meters. So boosting with hard start cap kit may come in handy, I keep one on the boat

[Jolly Roger]

you've got me there. What's a hard start capacitor kit - where from?

[dtrue]

Try "Supco" Super Boost purchase at any wholesale A/C supply. This is what I have here on the boat. Mine cost $9.60

You can even replace your dysfunctional relay if that is the culprit all much less than service call. Provide your supply rep. a copy of the schematic it will indicate the MPR mechanical potential relay or other such as 3or 4 wire relay.

Heck shoot me a copy of your schematic I can tell you in a second which one you need. DanT

[bppleas]

Don't touch the terminals on a cap until discharged. To discharge short terminals on opposite ends of cap. Mark wires for reassembly and remove. Using volt/ohm meter set to ohms. Apply meter probes to terminals and reading should rise or fall. Switch probes to opposite terminals and reading should go the other way. in other words the cap will store a charge from meter battery with probes in way and show a discharge with probes the other way. If it does the cap is good and if it doesn't it bad.

[John umbarger]

The compressor can be checked for ground. Also it has 3 terminals
Start, run, and common. You omm start to common, then run to common,
than run to start,

Example. Start to com 2 omms
Run. to com. 3 omms
Now. Run to start. 5 omms. This is what your looking for the compressor is OK
If you don't get numbers that follow the above its probley bad, if their off a
little bit your probley ok. Also you can check each terminal to compressor
case, scrap paint for good connectivity if you have connetnewity its grounded
compressor is burned out. Don't mess with gages just trying to check
You'll lose enough that will cause more problems, the charge needs to be
weighed in.
And if the unit has a low pressure control nothing runs if its tripped, most
Budget units don't have one. Capacitors are nothing to be worried about charge, and their cheap. Hope that's your problem

JOHN. Retired refit contractor

[SeaSon]

Compressor doesn't run. What does that mean? Does it try to run (hums), or never even tries? If it hums, the you've got a bad wire connection such as over heated or corroded, or the start cap. If it doesn't try, it's likely a logic issue (logic board, hi or lower pressure switch, relay). Try jumping across from the fan relay to the compressor relay, to determine if it's the relay or the logic prior to the relay. Cutting the wires to the high and low pressure switches is how I isolate them on my system from my logic board. Try jumping 24vac across the logic board from the input to the relay to see if it's in the logic system. The fan running means the transformer is good, you've got 24vac, the thermostat is sending at least a fan run signal, etc. The fan doesnt likely use the logic board, neither does coil heat. Good luck.

[GordMay]

Greetings and welcome aboard the CF, bppleas, & John.

[dtrue]

SeaSon, You sure gave the man a vivid explication, of the Marine compressor units. Well enough he can take it to youtube or google and walk all the way thru this. Good job, however its easy for you and I to say, still a learning curve for the novice.

I have found that corrosion is to blame more than failure especially on newer 10yr> I guess its the after market on the older vessels that doesn't use dielectric or solder or adhesive coated wire shrinks. All these little details have an effect years later.

Oh I have to acknowledge bppleas thanks for being spot on in your advisement on safety. Your recommendation dealing with the discharging of stored power as referenced, a capacitor. Right On

Reminds me of my childhood, we'd flip some one a capacitor in the shop from an older car or Pickup they were called back then in the late 60's....from under the old rotor points distributor caps ... and it was all funny because we didn't get shocked. I think it was a single pole capacitor we called a condenser back then.... wasn't it "points, rotor and condenser", ?? ahh I don't remember.. I should research to sound more...ah its not all that important. Been a long time. ; ) LOL Good luck, Dtrue

[Jolly Roger]

Hi Guys,
I want to thank everyone who has responded to my post so far.
I haven’t been able to remove the AC unit yet, on my own. It's up high in a locker and I can't lift it out myself, but I'll get help next week.
I wonder if this wiring diagram from the owner’s manual will tell you anything?
Just a thought - is it possible that a blocked evaporator radiator could cause the compressor not to work? I have cleaned the evaporator fins from the inlet side, but I can't get to the inside of the fins and I suspect they might be pretty blocked from five years of use, sometimes in a dusty work invironment.
JR

[Sailmonkey]

Originally Posted by Jolly Roger

Hi Guys,
I want to thank everyone who has responded to my post so far.
I haven’t been able to remove the AC unit yet, on my own. It's up high in a locker and I can't lift it out myself, but I'll get help next week.
I wonder if this wiring diagram from the owner’s manual will tell you anything?
Just a thought - is it possible that a blocked evaporator radiator could cause the compressor not to work? I have cleaned the evaporator fins from the inlet side, but I can't get to the inside of the fins and I suspect they might be pretty blocked from five years of use, sometimes in a dusty work invironment.
JR

a clogged evaporator with dust/dirt has nothing to do with the compressor either running or not.

From your schematic, I'll put my money on either the Control board, or either the low pressure switch or the high pressure switch (unless the whole thing looks like a pile of corrosion).

[pesarsten]

If the evaporator coil is clogged , it can prevent the refrigerant from absorbing the heat from the cabin air. This will cause low pressure in the suction line to the compressor and will cause the low pressure cutout switch to open ( if installed) . This will shut the compressor down. The compressor should cycle back on , shortly, once the refrigerant warms , and cycle off again.

[Sailmonkey]

Originally Posted by pesarsten

If the evaporator coil is clogged , it can prevent the refrigerant from absorbing the heat from the cabin air. This will cause low pressure in the suction line to the compressor and will cause the low pressure cutout switch to open ( if installed) . This will shut the compressor down. The compressor should cycle back on , shortly, once the refrigerant warms , and cycle off again.

Correct, but when I'm told the compressor does not run, I don't immediately think of short cycling.

[pesarsten]

Based on the schematic the high and optional low pressure switches are connected to the control board at a three pin connector at the edge of the board.

I would troubleshoot with the power Off as it looks like the control loop is line voltage. Power off , disconnect the connections ( label wires to be sure of where to put them back to ) and test the resistance of the loop between the center wire and each outer wire. It should read as 0 ohms. A high resistance would indicate a failed switch. the center yellow ( common) wire is yellow, the high is red and the low is blue.

Another common problem can be a failure at the compressor plug connector. One pin of the three frequently burns up when it overheats. Pull the connector off and inspect.


Paul

[Movinon1]

Since you have the luxury of having two identical units, Use the good unit to verify the bad. I would start by disconnecting the compressors from the logic board. Turn system on, and measure voltage at Logic board terminals. If these are different, i.e. voltage on good system, but no/low voltage on inop system, then there is a problem before the compressor. Compare resistance readings of good compressor to old. Open, or dead short would indicate bad compressor, or corrosion of terminals. You can try swapping known good components from good system into not working system, but do so knowing that you may windup with two non-working systems. I have been able to buy individual components, i.e. logic boards by searching on line using everything from model number to circuit board numbers. Have saved alot of money by ordering this way. Have found that dealers don't like to sell parts, without selling service also.