wrote in message
...
On 18 Jul 2006 10:49:31 -0700, "jamesgangnc"
wrote:

If you could find a thermostat with different on and off temps that
might help. Then you set it to come on at 72 but not go off until 68.
I know that heater thromostats have anticipator circuits to compensate
for cycling but I don't think ac ones do.

This actually may be a function within the digital control, setting
the temp differential......I need to dig into the manual for the
controller.....

Yep. The digital thermostats on my boat have a programmable differential.
I think the default is 2 degrees, but you can set it otherwise.

Eisboch

The problem is, the A/C will bring the cabin down to temperature, but
the temperature rises so quickly after the A/C cycles off, that it
cycles right back on again. I bought and installed the optional
remote temperature sensor, which I mounted in the return air duct, and
this helped a little bit, but did not cure the problem.

Mounting the thermistor (remote temperature sensor) in the return air duct
might be the problem. My Sea Ray came with the thermistor mounted right
next to the AC machinery, clipped to the drip pan, which if you think about
it, is really stupid. The factory default setting for the fan was to have
it run all the time, and as long as the fan was running it worked OK. But I
prefer to have the fan cycle with the compressor. When I programmed the
system to cycle the fan with the compressor, I had the same problem you
have. The problem was due to the close proximity of the thermistor to the
AC machinery. As soon as the fan cycled off, the thermistor would pick up
the heat radiating from the compressor and cycle the system back on almost
immediately.

It became quickly obvious that the factory location of the thermistor was
measuring the ambient temperature of the compartment that housed the AC
machinery, rather than the ambient temperature of the cabin. With the
constant airflow of a non-cycling fan, the two temperatures fairly well
equalized. But in a cycling fan situation, the temperatures of the
equipment compartment and the cabin diverge greatly and quickly once the fan
stops. Solution: Put the thermistor in a location where I live rather than
where the machinery lives. I purchased a thermistor with a long remote
cord, and snaked the thermistor out of the AC machinery compartment into the
living quarters of the cabin, and all was instantly well. Makes perfect
sense. Imagine if the thermistor for the AC system in your home was located
outside in the ductwork rather than inside the house. Problematic, at best.

"RG" wrote in message
...


Mounting the thermistor (remote temperature sensor) in the return air duct
might be the problem. My Sea Ray came with the thermistor mounted right
next to the AC machinery, clipped to the drip pan, which if you think
about it, is really stupid. The factory default setting for the fan was
to have it run all the time, and as long as the fan was running it worked
OK. But I prefer to have the fan cycle with the compressor. When I
programmed the system to cycle the fan with the compressor, I had the same
problem you have. The problem was due to the close proximity of the
thermistor to the AC machinery. As soon as the fan cycled off, the
thermistor would pick up the heat radiating from the compressor and cycle
the system back on almost immediately.



Agree. I had a similar, but opposite problem. The thermistor for the
master stateroom was mounted on a little plastic tab stuck into the
evaporator coils of the A/C unit. It worked fine if I ran the system in
continuous fan mode, but if I programmed the controller to shut the fan off
when the compressor shut off, the temperature readout would continue to drop
because there was no heat load on the cooled evaporator. I'd watch it drop
to about 10 degrees below the setpoint before it slowly started to climb
back up as the evaporator warmed back up. The temp in the room would
obviously cycle widely.

Cured that by simply mounting the thermistor away from the evaporator and
adjusting the controller parameters accordingly.

Eisboch

On Tue, 18 Jul 2006 12:51:26 GMT, wrote:

I went from the tried and true copper tube thermostat to a new digital
thermostat when I installed the new A/C, and I think the old
technology is more fitting for a boat, because I did not have cycling
problems with the old A/C system.

If you have the manual available for the digital thermostat you may
find that there are some programming options that can minimize short
cycling. I have converted both my fridge and freezer to digital
thermostats in the last year and there are 3 or 4 different parameters
that can be specified including "Delta T" for high and low set point,
and something called "ASD" which actally stands for "Anti Cycling
Delay". It allows you to specify a minimum time before it will trip
back on, typically at least 2 or 3 minutes.

On Tue, 18 Jul 2006 23:45:52 -0400, Wayne.B
wrote:

On Tue, 18 Jul 2006 12:51:26 GMT, wrote:

I went from the tried and true copper tube thermostat to a new digital
thermostat when I installed the new A/C, and I think the old
technology is more fitting for a boat, because I did not have cycling
problems with the old A/C system.

If you have the manual available for the digital thermostat you may
find that there are some programming options that can minimize short
cycling. I have converted both my fridge and freezer to digital
thermostats in the last year and there are 3 or 4 different parameters
that can be specified including "Delta T" for high and low set point,
and something called "ASD" which actally stands for "Anti Cycling
Delay". It allows you to specify a minimum time before it will trip
back on, typically at least 2 or 3 minutes.


Well, to my surprise, there's no temp differential adjustment on my
digital controller, and it's fixed at 2 degrees. There is a
compressor delay feature, so I'm going to experiment with maxing out
the compressor delay and running the fan continuously in hopes of
getting a better air mix and reducing the short cycling......

The best way I've found to stop the short cycling is just to put the
A/C on 60 and let it go......Everyone wakes up frozen, but it's almost
better than hearing that thing go off and on incessantly.....