Air conditioner failed

I seem to be having my share of problems with my air conditioning units.

I replaced the pump motor last month. After a day cruise last week, we hooked up electrical and the rear AC compressor would not come on, the fan worked. The digital control panel has a light that illuminates when the compressor is on. The light was on, but not the compressor, nor was the new pump motor. I turned on the fwd ac unit and it worked fine including the pump motor.

I located the computer module for the aft ac unit and observed several electrical terminals including 4 for the compressor and pump motor. I put a voltage meter on the input terminals and got 120 v but 0 volts on the compressor and pump motor.

I removed the circuit board from the boat after talking to the manufacturers tech. After describing the problem and the tests that I did, he said the board is most likely the problem. Upon removal I noticed a burnt spot on the underside of the circuit board where a relay is soldered to the board.

The manufacturers tech said a new board is $550. Impossible I said, there's not that much to it. Yes, I know, but they don't make that board anymore and you have to upgrade to a new system which includes a new digital control panel was his reply. But my current control panel is just fine I said. Tough luck he said.

After much searching I found the company that makes the circuit board. It was not easy, a small company in New Jersey. I called and in talking to the tech he confirmed that I nailed the problem. So I asked, can you fix it? Yes he said, for $200.

Problem solved. Cool air next week, I hope.

I shudder to think how much this would have cost if I had called a local marine AC repair place.

Congrats on having the fortitude to actually seek and find a repair! Too many times now days the repair people simply want to replace things because they can't actually figure out the problem.

Well done Tim. The more you understand it the less chance someone can BS you on a repair.

There's a bit of motivation to fix things my self, I couldn't afford this boat if I had to call some one to fix everything that broke. I hate working on the engine, but I always research the problem before I start and if I need help I already know the fix before I call a mechanic. Boatdiesel.com has saved me a ton of money.

timjet wrote:Upon removal I noticed a burnt spot on the underside of the circuit board where a relay is soldered to the board.

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*Chicken or egg?

Well the tech at MicoAir that makes the circuit board mentioned that the board does fail and I can't really remember if he said the electronic component that I said had a burnt spot at the solder joint has a history of failure. I'm assuming it's a relay but not really sure. Printed on the component is: Schrack TD 923005

I think what Rick and Mike are asking is; am I sure the board failed or is something else causing the component to blow out? I don't know, however what is happening is the board is not sending power to either the water pump motor or to the compressor. I know the water pump motor is working properly but I don't know if the compressor is at fault in blowing the relay or whatever blew out, by demanding more amps than the board can supply. How can I determine that?


-- Edited by timjet on Sunday 10th of July 2011 09:08:18 AM

I talked to the tech today and mentioned the possibility of the compressor demanding too many amps and causing the relay to fail. He confirmed that it was the relay that failed. He told me how to hook up the compressor directly to the power supply. Turn on the breaker and if the compressor runs, all is well and the problem is fixed. IF the compressor pops the breaker then the compressor needs to be looked at. He also mentioned that because the unit is 14 yo, most likely it's a bad relay. I will however do the compressor check before I attach the board.

Jet

Be sure to monitor amps as the compressor is started. You can check motor with VOM meter to be sure it isn't going to ground or otherwise BO. Did your AC or circuit board per chance get wet?

Tom,
The unit did not get wet. I will monitor amps closely when I turn the compressor on before I install the board. Thanks for the heads up.

Timjet,** I* had a simular problem with an AC unit the fuse on the circuit board kept blowing out.* The tech told me the water pump was drawing to many amps for the circuit board mounted relay.

I installed an external relay with higher amp contacts,* Now the circuit board water pump power out terminals only close the external relay (no real current thru the board).Never had*problem again.

In your case you could also isolate your board from high current.* The ouput to the compressor could be used to only close an external relay ( A 40 or 50 amp relay with a 110 ac coil would work )** With this set up no matter what happens with the compressor the board would only be dealing with the current to close the relay.

JohnP

*

JohnP wrote:
I installed an external relay with higher amp contacts,*

In your case you could also isolate your board from high current.* The ouput to the compressor could be used to only close an external relay ( A 40 or 50 amp relay with a 110 ac coil would work )** With this set up no matter what happens with the compressor the board would only be dealing with the current to close the relay.

JohnP*

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*John, thats a great idea. According to the tech, the relay that's on the board is good for only so many cycles. Those cycles are reduced when higher amperage flows through it. My other AC unit is the same age and I suspect it will go soon.

I think I'm pretty mechanically inclined, fixing most things on the boat and I know a little about electricity having rewired about half my aging house wiring. However I know very little about electronics. Could you PM me or tell me how to wire an additional load carrying relay? Also adding a fuse to protect the circuit board from current spikes created by a bad compressor or water pump is not a bad idea either.*


-- Edited by timjet on Sunday 17th of July 2011 01:28:17 PM

Tim

Like JP, I have a separate breaker for my cooling water pump. Each of three 3 Marine Air ACs*have their own breaker as well. So far trouble free but I'm not in FL using the units 24/7

OK guys, I got the circuit board back from the manufacturer. The relay was bad and they replaced it. I installed it and it is working fine.

I talked to the tech about the possibility of the compressor demanding too many amps, and he said to take the compressor power lead that's on the board and connect it directly to the power supply to the board. That eliminates power going through the relay. If the compressor does not pop the breaker then it's probably OK. That's what I did and it did not pop the breaker and the compressor did not make any unusual sounds.

Thanks to Rick and Mike for bringing that to my attention.

Concerning the wisdom of adding an additional relay to take the load of the circuit board relay, the tech highly advised me against that. He said the circuit board relay is rated at 100 amps, far more than the CB. Furthermore he said the relay had worked for 13 years and the new one would probably work as long.

I had a simillar experience with a circuit board on my heater.* Close examination showed an overheated* relay with the solder melted off the circuit board.* A replacement board was quoted at over $600 with a two week delivery.* Not having that much time or money, and having little to loose, instead I simply re-soldered the board.* It's been about five years now, and it still works fine.* .............Arctic Traveller

timjet wrote:

Concerning the wisdom of adding an additional relay to take the load of the circuit board relay, the tech highly advised me against that. He said the circuit board relay is rated at 100 amps, far more than the CB. Furthermore he said the relay had worked for 13 years and the new one would probably work as long.

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********* Tim,* Sounds like your in business,* With a 100amp relay in the board you are all set.

JohnP

Arctic Traveller wrote:
I had a simillar experience with a circuit board on my heater.* Close examination showed an overheated* relay with the solder melted off the circuit board.* A replacement board was quoted at over $600 with a two week delivery.* Not having that much time or money, and having little to loose, instead I simply re-soldered the board.* It's been about five years now, and it still works fine.* .............Arctic Traveller

Click to expand...

*I should have tried that. Would have lost nothing if it didn't work.

*

John, I e-mailed you about another issue I'm working on!!


-- Edited by timjet on Tuesday 26th of July 2011 07:29:51 AM