Tim --
I haven't looked at a schematic for one of these in years, but for what it's
worth...
The time delay (mars) relay is only used in the circuit at startup.
If the compressor is only running for a few seconds, then it's either
overloaded (possibly oil slugged) or the run cap is shot, which causes it to
draw too much current and trips the guardette.
The guardette is a small round circuit breaker on the side of the
compressor, usually right beside the start/run relay. It's usually under a
cover with a wire retainer that looks like a handle on can of paint. (bail)
For most sealed compressors, if you "remove the wire which we "THINK" is
from the compressor overload switch" it shouldn't run at all, since this is
a series circuit.
"The compressor actually gets quite cold in operation. Is this normal?"
No. It should be warm (or hot) rather than cold, depending on your local
temperature.
There may be some residual 'chill' on the suction (low pressure) line, but
the compressor probably isn't running long enough to get up to temperature,
so it seems 'cold'.
> Do I have a second bad Capacitor?
I'd guess that you do, or else the start/run relay is shot. Those are the
most common problems with these sealed units.
> I don't have the time delay so many have mentioned.
> Where can I get the "Mars" or equivalent relay?
If the circuit for the 'soft start' wasn't included in your roof top unit at
the time of build, it's difficult to add one in a simple and direct way.
Not having one isn't the end of the world, it just makes it easier on your
genset (and shore power connection) by making sure that the recirculating
compressed refrigerant has time to equalize (high side head pressure
reduces) before the compressor tries to start again.
Without the delay relay, the guardette on the compressor itself will trip,
or else the circuit breaker ahead of that will trip due to too much current
draw.
A fast recycle attempt has the compressor motor trying to start turning
against the remaining pressure from the previous run cycle.
It can't start to turn against this residual pressure, so it draws too much
current. To keep from burning out the windings of the motor (which is what's
inside the compressor, it trips the guardette (circuit breaker) which is
sized just right to protect the motor itself.
I'd try another capacitor first if your the home handy man type, or get a
local refrigeration person to take a look see at your problem.
Other than the fan motors they use, these roof top units are a lot like
window air conditioners, so a good appliance man can help you out. It
doesn't sound like you've lost your refrigerant charge, so its most likely
an electrical problem.
With R-12 no longer available and R-22 scarce (and expensive), if you toast
your motor windings, I'm not sure what you have left to work with, so you
might want to seek out a pro.
Those are my .02 worth.
Mark
> -----Original Message-----
> From: owner-gmcmotorhome
> [mailto
wner-gmcmotorhome]On Behalf Of LARRY DTIMOTHY
> Sent: Saturday, August 22, 1998 7:24 PM
> To: gmcmotorhome
> Subject: Re: GMC: A/C Mars relay
>
>{snip}
I haven't looked at a schematic for one of these in years, but for what it's
worth...
The time delay (mars) relay is only used in the circuit at startup.
If the compressor is only running for a few seconds, then it's either
overloaded (possibly oil slugged) or the run cap is shot, which causes it to
draw too much current and trips the guardette.
The guardette is a small round circuit breaker on the side of the
compressor, usually right beside the start/run relay. It's usually under a
cover with a wire retainer that looks like a handle on can of paint. (bail)
For most sealed compressors, if you "remove the wire which we "THINK" is
from the compressor overload switch" it shouldn't run at all, since this is
a series circuit.
"The compressor actually gets quite cold in operation. Is this normal?"
No. It should be warm (or hot) rather than cold, depending on your local
temperature.
There may be some residual 'chill' on the suction (low pressure) line, but
the compressor probably isn't running long enough to get up to temperature,
so it seems 'cold'.
> Do I have a second bad Capacitor?
I'd guess that you do, or else the start/run relay is shot. Those are the
most common problems with these sealed units.
> I don't have the time delay so many have mentioned.
> Where can I get the "Mars" or equivalent relay?
If the circuit for the 'soft start' wasn't included in your roof top unit at
the time of build, it's difficult to add one in a simple and direct way.
Not having one isn't the end of the world, it just makes it easier on your
genset (and shore power connection) by making sure that the recirculating
compressed refrigerant has time to equalize (high side head pressure
reduces) before the compressor tries to start again.
Without the delay relay, the guardette on the compressor itself will trip,
or else the circuit breaker ahead of that will trip due to too much current
draw.
A fast recycle attempt has the compressor motor trying to start turning
against the remaining pressure from the previous run cycle.
It can't start to turn against this residual pressure, so it draws too much
current. To keep from burning out the windings of the motor (which is what's
inside the compressor, it trips the guardette (circuit breaker) which is
sized just right to protect the motor itself.
I'd try another capacitor first if your the home handy man type, or get a
local refrigeration person to take a look see at your problem.
Other than the fan motors they use, these roof top units are a lot like
window air conditioners, so a good appliance man can help you out. It
doesn't sound like you've lost your refrigerant charge, so its most likely
an electrical problem.
With R-12 no longer available and R-22 scarce (and expensive), if you toast
your motor windings, I'm not sure what you have left to work with, so you
might want to seek out a pro.
Those are my .02 worth.
Mark
> -----Original Message-----
> From: owner-gmcmotorhome
> [mailto
wner-gmcmotorhome]On Behalf Of LARRY DTIMOTHY> Sent: Saturday, August 22, 1998 7:24 PM
> To: gmcmotorhome
> Subject: Re: GMC: A/C Mars relay
>
>{snip}
