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Splitting a split system AC unit

Discussion in 'HVAC' started by HaveADay, Apr 22, 2015.

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  1. HaveADay, Apr 22, 2015
    #1
    HaveADay

    HaveADay Member

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    Hello,

    On my boat I have CruisAir SMX split-gas AC system. The Salon and Pilothouse are served by two separate evaporators but there is currently only one thermostat controlling both of them. The thermostat is located in the Salon and seems to fully control the salon evaporator. The pilothouse evaporator seems to basically be a passive slave to the salon unit. There is no fan speed control and it just runs in high fan at all times. This makes the system both louder than it needs to be and means that there's no individual control of the pilothouse. There is a second split-gas system serving the staterooms and it works as expected. There are two thermostats for the two evaporators and though they are fed from a single condenser each stateroom can be fully controlled independently.

    I'm wondering what would be involved in splitting the thermostatic control of the pilothouse unit. I'm assuming I'd need something to adapt the condenser to allow demand from either of the two thermostats to cause the condenser to fire up.

    Thanks in advance for any help
    Ben
  2. Bamboo, Apr 22, 2015
    #2
    Bamboo

    Bamboo Senior Member

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    Are you sure you are operating the system properly? There should be a auto fan setting which cools to a preset level and then the fan slows and a manual setting. I'm not a professional marine a/c tech so I'll ask what is a "split gas system"? You should have a compressor and a air handler, or multiple compressors and air handlers. Have you looked over the CruisAir website or googled to find out more?
  3. HaveADay, Apr 23, 2015
    #3
    HaveADay

    HaveADay Member

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    Yes, I'm quite sure I'm operating it correctly. For the second evaporator (air handler) regardless of the fan speed being controlled automatically or manually the fan speed never varies. For the salon unit it responds to the thermostat appropriately. A split gas system refers to the fact that the condenser (compressor) and evaporator (air handler) are physically split and that the coolant gas, R134a in this system, is circulated between the components. I have two condensers on the boat and four evaporators. I've Googled extensively, looked at Cruisair's info and spoken to multiple cruisair dealers and distributors. Thus far I've not found anyone overly interested in helping. The knowledgeable folks want to refer me to the local service folks and the local service folks seem to know how to do little more than check gas levels and replace failed components.

    Ben
  4. NYCAP123, Apr 23, 2015
    #4
    NYCAP123

    NYCAP123 Senior Member

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    Also not an AC guy, but it seems to me that you should be able to install a switch (ordinary light dimmer) directly to that fan to slow it. It wouldn't affect the cooling, but only the fan. I'd suggest getting in touch with an electrician rather than an AC guy.
  5. K1W1, Apr 23, 2015
    #5
    K1W1

    K1W1 Senior Member

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    Are you saying you have one compressor, two condensers , four evaporators and 1 thermostat?

    If the compressor and condenser are physically split the system will not work, they each need each other to make the system work no matter what you are using for gas.
  6. mwwhit1, Apr 23, 2015
    #6
    mwwhit1

    mwwhit1 Senior Member

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    I have your same setup in my two cabins. Still have the old 3 knob controls, but shouldn't make much difference for the SMX. Master stateroom has the full controls and the side stateroom has just a rotary knob (like NYCAP mentions) to control only the fan speed. Your pilothouse fan has to connect to some kind of 110 source tied into the AC system that turns it on. Wiring a dimmer\rotary switch in that circuit will give you fan control.
  7. K1W1, Apr 23, 2015
    #7
    K1W1

    K1W1 Senior Member

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    If you pump refrigerant through an evaporator with the fan off or running too slow you risk freezing the evaporator.
  8. Bill106, Apr 23, 2015
    #8
    Bill106

    Bill106 Senior Member

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    If you have an R series compressor all evaporators will have to run at the same time and fan speeds are paralleled, both units will run the same fan speed or you will have freeze up as K1W1 cautioned. Only the newer RM series modulating compressors and the tempered water systems will allow true independent zone operation. If you have the R series you will not be able to do what you are asking unfortunately but you could upgrade to the RM series with the EHMB air handlers and use the existing piping.
  9. HaveADay, Apr 23, 2015
    #9
    HaveADay

    HaveADay Member

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    Bill,

    Thanks for the info. Definitely helpful. For the salon and pilothouse the condenser is FX-48RC1 with R22 (I was mistaken earlier) and it has a single thermostat controlling it. For the staterooms the condenser is a FM24C-PV, also with R22, with two separate thermostats controlling it. For the staterooms there will be frequent times when only one evaporator is running. Is it possible there's some sort of valving that stops the powered off evaporator from having gas circulate in order to avoid the icing condition?

    Thanks
    Ben
  10. K1W1, Apr 23, 2015
    #10
    K1W1

    K1W1 Senior Member

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    Yes, it is called a solenoid valve but will only work of the evap the line you are closing off is the end of the line and the outlet returns to the compressor or you will end up stopping the supply to all of them downstream.

    Get the valve to shut when the fan drops to a certain speed or stops and to open when the fan either starts or reaches a certain speed, the control could probably be done with a flow meter of some sort.

    The exact arrgt is best examined by an AC guy to get it right first time.

    Also, I am not sure what the deal is in the US with R22 and its components, at the very least you will need a guy to recover and re use it if fitting a valve in the line.
  11. Capt J, Apr 23, 2015
    #11
    Capt J

    Capt J Senior Member

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    If it isn't the new style, then both units Pilothouse and salon fans/evaporators need to run so the fan coils don't freeze and also so the compressor doesn't run high head pressures and result in a very early death, because it is sized for both evaporator units.
  12. NYCAP123, Apr 23, 2015
    #12
    NYCAP123

    NYCAP123 Senior Member

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    Well HaveADay, looks like your answer is that it's the nature of the beast. The pilot house fan runs full on because it has to. Sounds like your only cure is installing an independent unit.

    P.S, Today I learned a little more about air conditioning. It's a good day.
  13. HaveADay, Apr 24, 2015
    #13
    HaveADay

    HaveADay Member

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    I've learned a good bit as well. I was able to verify that my stateroom AC unit is a modulating unit as was mentioned earlier in the thread. So, the Salon unit isn't, meaning both evaporators need to be run at the same time. It would seem likely to me that as long as one doesn't turn down the blower too low it should be possible to modulate the pilothouse blower some. I'm going to inspect the current wiring to see if there is a way to connect the blower power for the pilothouse to the variable voltage output of the salon.

    Thanks all for your input and help. Very informative.

    Ben
  14. Pascal, Apr 24, 2015
    #14
    Pascal

    Pascal Senior Member

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    On my 53 the factory set up has one compressor for both smaller guests stateroom. In one stateroom is a standard digital control (originally the ole 3 knob cruisair control) and the second one has a single rotary knob to control the fan speed. You can set the fan low and not freeze the evap although you can't turn it off obviously.

    I don't see why you couldn't do that in your case
  15. Capt Ralph, Apr 25, 2015
    #15
    Capt Ralph

    Capt Ralph Senior Member

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    Pascal has it.
    Bertram did the same thing. You can never turn the fan off. Just slow it down a lil and reduce the noise a bit. I'm sure a knowledgeable marine A/C guy can order one for you from Dometic. A light dimmer will not work.

    If you still have problems finding one, let me know. I have one or two old 3 knob stations in my mini warehouse.