McQuay RPS intermittent failures to start

[Zuni]

Has anyone had problems with units attempting to start and then resetting in as soon as the contactor pulls in? Or the contactor chattering on start and then failing to start.

I have been looking at the relays and timers, but nothing is consistent. So I cannot identify the problem.

I hate to start parts changing!

[Mcgushvac]

If you give complete M# and S# will know what type of controls are in it. Most likely bad
output board relay if it is that vintage.

[referman10]

Has anyone had problems with units attempting to start and then resetting in as soon as the contactor pulls in? Or the contactor chattering on start and then failing to start.

I have been looking at the relays and timers, but nothing is consistent. So I cannot identify the problem.

I hate to start parts changing!

I have the same problem with a York YCA440, Ive changed the High pres switch,control relay, and relay output boards and contactors. Still shuts down as soon as it starts on Current/HP alarm. Ive even changed the CT mod. I had York come out and they cant figure it thats when we started parts changing.

[shakespiare1]

I have the same problem with a York YCA440, Ive changed the High pres switch,control relay, and relay output boards and contactors. Still shuts down as soon as it starts on Current/HP alarm. Ive even changed the CT mod. I had York come out and they cant figure it thats when we started parts changing.
Check is the rate of contactors coils voltage are correct for the application in some cases factories load units with the wrong components. also contactors itself they could come defective from factory.
Do this desconect the coil for one of the contactors and see what happens if the problem continues conet thatone back and do the same with the other one. if the problem continue check voltage going to your coils if 24, 110, or 208 or so and see if they match it up with whatever your contactor says.
This is what i mean.
One time i spent a full day trying starting a unit brand new, i`m not gonna mention brand name ok but, after spending creazy time there i noticed that the voltage for the unit was 208 v but my compressors were 460v.
noway this compressors would run, hey idf was runing also condenser fan were runing

[shakespiare1]

Zuni I think i answered you quetion to somebody el by mistake:gah:

[Zuni]

Thanks Mcgushvac,

Model# RPS090CLA
Serial# FB0U010300231 02

I thought about someone else was saying and disconnecting the coil on the contactor, checking voltage there and see what happens.

I was wondering what I might see if I disconnect the load side of the contactor and see if it does the same thing with no load.

[referman10]

I think that disconnecting the load side is a great idea, I will try that next week and post my results. Like the other guy, its not consistant. This is the kind of stuff you go home with at night, makes you crazy!

[duke of earl]

I had a Trane Self Contained unit that I was starting up years ago. As soon as the compressor contactor pulled in, the lockout relay tripped. After much struggling, I found that the impact of the contactor pulling in was causing enough vibration to trip the reset relay. I removed the reset relay from the panel and let it float. No more lockout!

[hevac1]

Is this MT2 or MT3? What are the timers setting? Timer settings, 180 sec for startup, recirc, & lowtemp. 30 Sec Flow. there are others but not important at this time. If the airflow timer is at 0 then the unit will go into restart as soon as it starts. Does the controller reset turn off & back on or does it just go into restart on the display? Are there VFD's? Have you called Mcquay and talked with Brad?

[supertek65]

I work on hundreds of RPS units!
Had every problem in the world!
The only time I ever had a unit that did this was a problem with high duct static switch, freeze stat and ofcourse the overloads!

what kind of controls are on this thing?
w-7100 controller, microtech, what operates the duct static?
VFD, IGV pneumatics or DDC?

just wondering?
I am not a mcquay mechanic and do not know serial number???????

[mikeymed8]

Did you ever find a solution to the outputs chattering?

I'm having a very similar issue. I have a RPS090CLY equipped with VFDs on the supply and return fans. Occasionally the supply and return fan contactors would chatter and lock the unit out on a fan failure alarm.

I've been through everything on the control circuit for the fans

- Went through the complete start / stop circuit from the output board to the fan contactors. Every connection was good and tight.

- Fan contactors have been replaced

- McQuay output board has been replaced

- Relays that plug into output board have been replaced

There isn't much left here to go wrong. I'm leaning towards the Microtech control board. It's a very basic circuit to pull in the fan contactors. I'm getting very frustrated with this unit as well as my customer. Any ideas would be greatly appreciated.

Thanks,
Mike

[Tech Rob]

Have you checked the 5 amp fuses on the output board or the MOVs on the back of the output board?

[mikeymed8]

Fuses are good. What do you mean by "MOVs"?

Thanks

[Tech Rob]

Metal Oxide Varistor. Think of it as an electrical sponge that absorbs the voltage surge that is developed when the output relays open and close. They can fail and will cause output problems. They usually blow the fuses, though.

[referman10]

Did you ever find a solution to the outputs chattering?

I'm having a very similar issue. I have a RPS090CLY equipped with VFDs on the supply and return fans. Occasionally the supply and return fan contactors would chatter and lock the unit out on a fan failure alarm.

I've been through everything on the control circuit for the fans

- Went through the complete start / stop circuit from the output board to the fan contactors. Every connection was good and tight.

- Fan contactors have been replaced

- McQuay output board has been replaced

- Relays that plug into output board have been replaced

There isn't much left here to go wrong. I'm leaning towards the Microtech control board. It's a very basic circuit to pull in the fan contactors. I'm getting very frustrated with this unit as well as my customer. Any ideas would be greatly appreciated.

Thanks,
Mike

No Mike , my problem ended up being a bad CT, after York told me to replace 7K in boards , contactors and relays I replaced the CT which they said worked or didnt, that fixed it. It does sound like a voltage problem in your cuircuit bd.( weak contacts) Ive had this many times, it drives you nuts!!

[Tech Rob]

After thinking about this more, you could have a problem with the ribbon cable from the MCB to the OBA.

[Zuni]

Sorry, I haven't got back to ya'll on this sooner. After a little monitoring, studying sequence of operation, schematic and timing lockouts, I figured out I had a bad low pressure switch (mounted on the compressor). I think, the vibration from the compressor starting would cause the contacts in the switch to shatter, causing the main contactor to chatter and lockout sporatically(sometimes). I verified the switch was opening (sometimes)with suction pressure above it's cut-in. Changed the switch and life was good.

I think I could have used the KISS principle sooner!

Thanks for all your input. Gotta go now, I have an RTU calling my name.

[Tech Rob]

I'm glad you got it figured out. Were you actually getting cool fail alarms? That's the only thing that will "lock out" mechanical cooling, besides outside ambient, and the unit won't tell you if cooling is locked out on low outside ambient...

There's only 3 things that will throw up a cool fail alarm on this unit; motor protector, high pressure switch, and oil pressure switch.

[mikeymed8]

I spent a few hours yesterday testing everything possible out on the unit. I spoke with McQuay tech support. I was told that if the DC voltage feeding the output board drops below 5vdc, it can cause chattering of the outputs.

Needless to say, I had a solid 5Vdc on the output board and the outputs didn't chatter once. I also tested all of the control transformers that feed the Microtech controller. I believe they were transformers T2 and T3. There is a 120vac to 24vac transformer and a 24vac to 18vac transformer that feeds the Microtech board. Both of them are delivering the proper voltage.

McQuay didn't have a solid answer as to why my outputs are chattering. I was told that another customer is having the same exact issues.

Like "BergerMech Rob" mentioned I ordered a new ribbon cable from the Microtech board to the output board to rule out the possibility of it causing issues.

I'll see how it goes and keep you guys posted

Thanks!