> -----Original Message-----
> From: owner-gmcmotorhome
> Sent: Monday, August 17, 1998 3:02 PM
> Subject: Roof A/C
>
>
{snip}
>> ...the compressor doesn't kick in for 60 to 90 seconds.
{snip}
> Has this unit always behaved this way as long as you've owned it or did
> it just start doing this recently.
Most of the 'premium' roof top units have this feature, for exactly the
reason Patrick goes on to explain..
> This was a safety feature to prevent compressor damage if the power went
> out and came back on quickly. It allowed refrigerant pressures to
equalize
> before the compressor restarted.
Correct. The time delay unit is a "mars" relay. It easier on the roof top
unit than tripping the 'guardette' circuit breaker on the compressor motor.
I would propose that the GM units all had mars relays them to keep from
doing some serious damage to the Onan.
The genset would nearly buckle in two (or at least make toast of the
generator windings) under the load of trying to start a locked compressor
motor in a roof top unit, let alone try to start two of them at the same
time.
Side note: All telephone company central offices that have gensets use this
same relay today to prevent the central air units from trying to re-start
too quickly after the loss of commercial power.
The 60-90 second compress or startup delay isn't a bug, it a feature!
Mark Grady
mgrady
> From: owner-gmcmotorhome
> Sent: Monday, August 17, 1998 3:02 PM
> Subject: Roof A/C
>
>
{snip}
>> ...the compressor doesn't kick in for 60 to 90 seconds.
{snip}
> Has this unit always behaved this way as long as you've owned it or did
> it just start doing this recently.
Most of the 'premium' roof top units have this feature, for exactly the
reason Patrick goes on to explain..
> This was a safety feature to prevent compressor damage if the power went
> out and came back on quickly. It allowed refrigerant pressures to
equalize
> before the compressor restarted.
Correct. The time delay unit is a "mars" relay. It easier on the roof top
unit than tripping the 'guardette' circuit breaker on the compressor motor.
I would propose that the GM units all had mars relays them to keep from
doing some serious damage to the Onan.
The genset would nearly buckle in two (or at least make toast of the
generator windings) under the load of trying to start a locked compressor
motor in a roof top unit, let alone try to start two of them at the same
time.
Side note: All telephone company central offices that have gensets use this
same relay today to prevent the central air units from trying to re-start
too quickly after the loss of commercial power.
The 60-90 second compress or startup delay isn't a bug, it a feature!
Mark Grady
mgrady
