RAUCC40

[milkyway]

Working w RAUC 40 split system
CIR 1 has 2 compressors
CIR 2 has 2 compressors,.
The condenser is tied into a 100% outdoor air unit ( AHU )
M Series climate changer.,
Air handler has cooling coil and heating coil.,
Air handler has mp581 controller With display.,
Now , I checked all the set points in the controller and they are satisfied,
Discharge air temp and set point , satisfied
Cooling coil temp and set point satisfied
Ect,
The problem I am having is , first of all even though the mp581 controller is satisfied, it is still Calling for 100% cooling., continues to run, no alarms on controller

Space temp feels ok but I did not actually check space temp thermostats./ temp sensors
I guess this could be the problem., one more question.,
System is r22 and running about 50 lb suction ., In normal situation I would add gas., but because 100% fresh air , could this be design to cool and dehumidify then reheat ? System Does need to be reset by the toggle switch occasionally , I am thinking due to low pressure, another tech was out there for a full day and I only had 1 hour to check .,
Also both condenser damper motors were inoperative (closed), which will cause high head, ordering those

any ideas

[jayguy]

...Also both condenser damper motors were inoperative (closed), which will cause high head, ordering those...

there is a switch (CW/CCW) on the damper motor that may be set incorrectly.

also, SATISFIED and AT SETPOINT are 2 different things. if the discharge air temperature is 55.0F and it took all 4 stages to get there, then it wouldn't ask for fewer stages of cooling even if the discharge air temperature was 55.0...maybe not even if it was 54.0F...it is going to wait until it gets below the differential before it starts shutting down the stages. and like you said, there could be a dehumidification issue.

low suction pressure could be caused by many things...

1. low load (which can be low temperature, low humidity or both or low air flow or all of the above)
2. underfeeding expansion valves
3. low charge...which causes the underfeeding
4. undersized suction line...what is the suction line pressure at the airhandler?
5. this unit is supposed to have a field installed suction line filter drier...what is the pressure drop across it?
6. this unit has field installed expansion valves...are they sized properly?

[rtac]

It would be nice to know how the MP 580 was set up for ...have you got Rover

[stanbyyourword]

I had a similar job in march 100% outdoor air unit, prior conversion to m099, I banged my head on the wall trying to get normal suction pressures , but max r/a was 60- 65f, in 45psi suction range , Told them have to return when its warmer, hope this helps stan

[milkyway]

its saturday,. kinda summertime here in central fla,
think i will go back out there., today., single, no kids this weekend,
what the hell,

jay, the condenser fan motor dampers do have the (cw / ccw ) setting.;, I saw that on there, however, those things would not move ., lol., shot!!!
thanks,


stan, i am believing that this is causing the reset that i am having to do every now and then.,



rtac., rover is a programming tool., the mp580/581 can be used for many things., such as lighting., alarms., antthing really., remember its a PROGRAMMING TOOL NOT A SET UP AND CONFIG TOOL.,


i will keep u guys posted ., thanks for the replies

[rtac]

Best of luck and keep us posted

Phil

[stanbyyourword]

in low ambients with these units such as emergency rooms , they use hotgasbypass, but if you have good load return air ie above 70, you will need to find why suction pressures low, stan

[Tech Rob]

WOW. Lots of possibilities with this one. Is there hot gas bypass? Is it factory or field installed? Does it use the liquid line solenoid valves for a pumpdown cycle or are they used to isolate the refrigerant charge only? Lock the top hats open until they're fixed. If the unit's locking out, it's probably on high pressure due to the top hats being broken.

What is the approximate size of the air handler? Are there outside air/return air dampers? If this thing was designed for outside air only, you may well have a 40 ton condenser, and what appears to be an air handler with only 15 ton 20 tons worth of air. The evaporator coil may be noticably thicker than a standard DX coil. This is because 100% outside air systems are almost always designed for high delta T and low airflow down to 125 cfm/ton in some instances. This is done to wring as much moisture out of the air as possible and provide low dewpoint air to the space. The expansion valves need to be sized for the capacity of the circuit, not the model # of the air handler. I had a job last year with 4 dual circuit 30 ton RAUC condensers, and at each air handler, there were 2 30 ton expansion valves on each circuit. Total of 120 tons of TXV for 30 tons of cooling.

Jay also mentioned suction line/suction drier, and that is another thing that could be causing low suction.

Rover is the only way you're going to see the programming in the MP580. However, what you have to do is run the thing wide open and see if there is an issue with the hot gas bypass, charge, or airflow. Start with refrigeration 101 stuff.

[Dallas Duster]

What kind of superheat and subcooling you got going on there? It is possible when temps were satisfied that it was in some kind of hot water reheat mode? I assume the unit is temp and humidity controlled?

[Healey Nut]

How about we used the KISS theory here ........
Is it wired correctly ??
And whats the sequence of operation ?

[stanbyyourword]

thats what i was thinking graham , its not low load cos he is florida w 100% osa , maybe controls , stan

[milkyway]

I am going to spend one more day on This due to I had no real time to thoroughly check myself, if I'm lost , plan on calling out the big boys., either way, I will let u fellas know one way or another, thanks

[jayguy]

How about we used the KISS theory here ........

to Rock 'n Roll All Night and Party Everyday?