AC / Heater won’t start

[Pat T]

Have Marine Air System. I have 3 units with one water pump. When pump is on it pumps water through all units whether or not they are on or off. Two units function normal. One unit turns on and only turns on the fan. The compressor or water pump are not activated with this one unit on heat or AC. Coils not icing up and no blockage in water lines. I have digital controllers for each unit. Appreciate your help.

 

[O C Diver]

Any error codes on the thermostat?
Is the thermostat in the correct mode?
Temperature in the correct range?

Ted

 

[Pat T]

Any error codes on the thermostat?
Is the thermostat in the correct mode?
Temperature in the correct range?

Ted

Thanks. No error codes. Thermostat is in auto mode. I changed to cool only and then heat only modes to see if I could get it to start but no luck. Ran the temp up and down and no luck.

 

[Madhatter53]

Bad capacitor or triac ?

 

[tiltrider1]

Bad capacitor or triac ?

Very likely a bad transistor or damaged circuit board. Get a multimeter and follow the electrons from the power in to the compressor and see where they stop.

 

[Pat T]

Bad capacitor or triac ?

Thanks. Not sure how to check either of those but I was able to contact Marine Air Systems and they asked me to swap the controller with one of the ones that was working. I did that to prove it wasn’t a controller issue. They said then that the most likely problem is a pc control board or called a unity board. Still waiting for them to get back to me with a price but looks like a minimum of $400 plus.

 

[Sababa]

Thanks. Not sure how to check either of those but I was able to contact Marine Air Systems and they asked me to swap the controller with one of the ones that was working. I did that to prove it wasn’t a controller issue. They said then that the most likely problem is a pc control board or called a unity board. Still waiting for them to get back to me with a price but looks like a minimum of $400 plus.

Having the same problem on one of my MarvAir units. Check (or have an electrician check) whether the leads from the board to the compressor are being energized before you replace the board. It could be that the board is fine but the compressor is shot, which is unfortunately my situation.

 

[Pat T]

Having the same problem on one of my MarvAir units. Check (or have an electrician check) whether the leads from the board to the compressor are being energized before you replace the board. It could be that the board is fine but the compressor is shot, which is unfortunately my situation.

Thanks Sababa. Just wondering if only the compressor is bad would the water pump also not run? Does your water pump still run with the failed compressor?

 

[Sababa]

Like yours my water pump is separate and feeds all four units on the boat. It’s working fine. The electrician narrowed it down to one of the coils that is part of the compressor. Still waiting for the HVAC guy to advise if it compressor can be replaced or if I need to install a whole new unit. Unfortunately, MarvAir, like many brands, has been acquired and retired by Dometic, who will no longer supply parts. Fortunately, it seems that compressor may be a standard part that is still manufactured. Here is the electrician’s diagnostic report:

Existing unit SPB24RCAR-P1

Single phase Copeland compressor
Start-Common coil - ~2.8 Ohm
Run-Common coil - Open Circuit
No coil to chassis short

Measured at compressor connector with compressor “cold”

 

[tiltrider1]

The fact that the water pump doesn’t turn on suggests that the compressor is fine. I still think it’s a transistor or burnt circuit board.

 

[Sababa]

I saw that the other two units were working and missed that the pump was not going on when you activated this one. Agree that it’s probably the board.

 

[Pat T]

Thanks guys. Another thing in my favor is that this looks like a newer compressor. Definitely newer than the other two so likely it is good. Tried to get in to see if I could get a meter on the compressor leads but it’s to tough to get at. This compressor and a slightly smaller one are outboard of the stb. engine (v8). Changing the board will be a pain.

 

[O C Diver]

Another thought:
Many, most models now measure return air for temperature. Older models used the thermostat display as the temperature sensor. It could be that the failure is in the temperature sensor. On newer models, the control board contained the temperature sensor circuit. On the older style with the temperature sensor circuit in the wall thermostat, you could replace the thermostat.

Maybe post a picture of the thermostat or check the unit for a wire hanging in front of the return airflow that would indicate the temperature sensor was on the control board.

Ted

 

[Pat T]

Another thought:
Many, most models now measure return air for temperature. Older models used the thermostat display as the temperature sensor. It could be that the failure is in the temperature sensor. On newer models, the control board contained the temperature sensor circuit. On the older style with the temperature sensor circuit in the wall thermostat, you could replace the thermostat.

Maybe post a picture of the thermostat or check the unit for a wire hanging in front of the return airflow that would indicate the temperature sensor was on the control board.

Ted

Thanks for chiming in Ted. The Passport II controller (display) that I have does indeed measure the temperature from its face plate. I was able to swap one controller for another, known good controller, and unfortunately I still could not get things to work. I wish the controller was the issue as it is likely half the price of a pc board and a whole lot easier to install !

 

[Pat T]

Just to follow up. I purchased the control board and also had to purchase a control display to go with it. Add in a new cable and got in for just under $850. Getting to my compressor was a PIA but all runs well.