View Full Version : lennox rtu high pressure switch
07-07-2004, 06:16 PM
Have several accounts with lennox GCS24-813-130-1Y units on the roof.Units are 10 years old or older.Have been getting calls About no cooling.Been finding the units tripped on manual reset high pressure switches.Swiches are suposed to trip at 410psi(got that from Lennox).Pressures are normal every time I check them.280 or 290 is the top head pressure I have seen.I was there tody.Unit was running.I shut the unit off at the disconnect.When I went to turn the unit back on,the head pressure switch was tripped.How or why are these things tripping after the unit is shutting down?Has any one else seen this?
07-07-2004, 09:54 PM
Are those gas packs or heat pumps? Had a bunch of GCS16 heat pumps with the switches you are talking about (red switch with the rubber push button) and if the defrost thermostat was bad and closed the unit would go into "defrost" in the middle of the summer. Of course the reversing valve was already in the cool mode but the condenser fans would cut off and trip the pressure switch. By the time we would get the service call, the timer had terminated the defrost cycle. Occasionally in the summer simply killing the disconnect would seem to "shock" the unit when the reversing valve dumped and cause the switch to trip.
07-07-2004, 10:09 PM
they are gas pachage units.Thanks for the input though
07-07-2004, 10:28 PM
OK, I'll offer you this. We purchased some inexpensive temperature recorders called "Hobos" that have a variety of uses. One thing I have used them for pertains to your problem. If you are trying to see when the problem is occuring you can put the temp. recorder in the supply airstream and tell when it is cutting off. Sometimes the "when" will point you towards the "why". Had a chiller locking out on a freezstat and used the recorder (with the available input lead) to determine that the chiller temp actually was getting that low because the temp controller was sticking but only occasionally. It was driving us nuts because it would trip in the middle of the night every three or four days. By the time the customer called in the morning, the building conditions were lost for the day. Also check the condenser fans for bearing wear and check their temperature to make sure they are not occasionally cutting off on thermal overload and causing the switch to trip. Good luck.
07-08-2004, 12:16 AM
why don't you just replace the switches and if they don't tripp then your good if they do trip then put a tee in where your pressure switch is connected and check your pressure at the same spot.on second thought just install a tee anyway when you replace switches
07-08-2004, 09:56 PM
check the condenser fan motors real close could be over heating from a dirty coil or worn bearings. Another thing to check would be the condenser fan relay, some Lennox unit used a clear ice cube type relay that could be real intermitent.
07-08-2004, 09:56 PM
you need to look at the condenser fan relay. I've had to replace alot of them. Also check your stat & wiring diagram. some GCS24's have only 1 condenser fan relay & it's only energized when "Y1" is calling. if "Y2" is somehow coming on 1st = no condenser fan causing hp switch to trip out.
07-08-2004, 11:25 PM
Just a question?Are the condensors double row coils & if so did you split them & clean them?
07-08-2004, 11:56 PM
the guy stated that the pressures never got above 200 lbs so condenser fan motor or relay is not the problem. more than likely just a bad switch or he has a restriction and is guage is hooked on the backside of that restriction and hes not seeing the pressre.
07-09-2004, 07:15 PM
Have either replaced them with one on the liquid line or moved the existing one if the gas was out of the system for any reason. A manual reset limit that close to the compressor on the discharge line is a nuisance trip waiting to happen.
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