View Full Version : York RTU
10-29-2006, 10:29 AM
I just accepted a new job as the service tech for 10 McDonald's restaurants in my area. The majority of the systems are York Sunline 5 ton RTUs. Although I have worked on these types before, I am not well versed in these typpes of units, and am not yet familiar with all the control components. I have mostly experience with residential split systems. One of these units will run for about 3-10 minutes (not always the same amount of time), and shut off. If I turn off the main disconnect on the unit and turn it back on, it will come on again. I was wondering which of the controls may be causing this. Such as Phase loss monitor, Low Evap Temperature Switch, etc. By the way: Where is a Remote Minimum Position Potentiometer located, and what is an auxillary limit switch for? Any assistance with these questions is appreciated.
Not for sure on the sunlines but maybe your having a pressure control opening-
10-29-2006, 08:47 PM
If the phase loss monitor cycles the unit you should be able to recover the cause thru the display on the phase loss monitor. The unit sounds like it is locking out , this is generally from high pressure, low pressure or the freeze-stat opening. Check the operating pressures and anything that could change the air flow like air filters, belts, evaporator coil surface, fire /smoke dampers or the drive sheave combination on the blower. The min. pos. pot. iswhat set the outdoor air damer to a min. open position, it is generally located on or near the economizer damper actuator.
10-29-2006, 09:55 PM
Congratulations on your new promotion. These units are pretty straight forward and after a cooling and heating season under your belt, you will be an expert at this unit. Get your hands on an IOM for this unit and start learning. I may be able to scan one if I can find it. If you have to recycle power, then you are locked out by the board on a fault. I assume that you are in "Heating" now and you may be faulting out on a flame failure. If memory serves me right, this unit has an auto reset rollout, but if the board sees it open, it will lock out the flame box. Is the inducer running when you come up on the unit? Good luck.
10-30-2006, 08:37 PM
I am in Waco TX. We are not in heating quite yet. I have checked the pressure switches during and after cycling off. They are closed throughout. Is the Freeze Stat. the same as Low Evap Temp Switch?
On the Schematic there is a range for FSI (Low Evap Temp SW) 26-41 Deg. F, and LAS (?) 55-45 Deg. What is LAS (not defined on Schematic)? Low Ambient SW maybe?
The schematic is helpful, but my familiarity with some of these controls and what they look like is lacking. I am assuming the Phase Loss Monitor on this unit is the "Relay" in a clear plastic case. There are no controls or display on it.
I apologize to all you guys who went to school for this profession. My training has been three years under a very wise Master Level Technician who taught me very much, but obviously not all I need to know (especially on these type units).
What does IOM stand for, and where can I get one? Through Johnson Controls, or York? I appreciate all your help.
If you could scan one and email it to me that would be fantastic.
10-30-2006, 10:43 PM
I dug and dug and all I found was an install manual. No wiring diagram. IOM stands for Installation, Operation and Maintenance and is probably a Trane term, but I use it interchangeably. Tell you what, you probably could find it at Yorks website. If I had it I would send it to you. Here in Virginia we have a unitary York supplier, Virginia Air, and you could get the IOM from whoever sells Rooftop parts for that unit. Post a full model and serial and I bet NormChris could help. Now, were is this LAS wired in the diagram? Can you post a few readings? I'll tell you what the main things needed are Suct Press and Temp, discharge pressure and temp, along with liquid line temp. I bet you don't have a liquid pressure port on this unit. Get amp draws and here is a big one: air entering evap and air leaving the evap. I know it sounds like a lot, but these readings can be taken in a snap and you will learn something by doing this. It sounds like you want to get this right and I know you will.
Now look, Eric, I am stretching my memory here, but I think what you have in the refrigeration circuit here is a couple of safeties that will , when opened, lock out the board. You probably have HP, LP and freeze stat. Any of them open and wham, the compressor locks out. Do you know what a "Tattle Tail" is? You MAY be able to catch the problem with one of these. Good luck and keep us posted.
10-31-2006, 03:39 PM
If you are working on heat, like another poster said, there is an auto reset limit switch above the burners, it get's weak, drops out, locks out the ignition control and no heat.
It will get worse as time progresses, but I am willing to bet that's what's wrong.
10-31-2006, 08:41 PM
As stated before, I am still in cooling mode. I haven't been back to the unit in question yet this week. I have been working on other issues, at other locations.
I don't know what a "Tattle Tale" is.
Again: Is the freeze stat the same as Low Evap SW? I appreciate everyone's assistance.
M/N: D4GC060N08225 MAC
10-31-2006, 09:09 PM
FS1 is the same thing as the freeze stat. It is a low temp cutout on the evap in case you loose the fan. The only thing close to LAS I see is a LS, which is a Limit Switch. I am looking at a diagram for a different series York RTU, but I think it will get us close. If you are running in ac, lets forget the Limit Switch for now. A tattle tale may help you here. Do you have an ARS supply house nearby? Any would do, really. A tattle tale is a device you wire around a device (like a freeze stat) to see if it is intermittently tripping. There is a little window with a red "flag" that will pop out if that switch is opening when you are not there. I know that you are busy, but when you get back to this unit, log it out and we can go over what you are seeing. The clear relay that you described is likely an inducer relay or a lock out relay. Let us know how you make out.
11-04-2006, 09:55 AM
Although it is not of consequence to the situation, I discovered that the clear plastic device is a Draft motor relay. Working on heaters now, which is a completely different animal altogether. I will keep you abreast of my findings.
11-05-2006, 03:41 PM
OK, draft motor and inducer are the same thing. Good. Keep us posted.
First of all are you sure you are getting a cooling call at y1. If you are and the unit is locked out restart and check pressures and superheat and subcool if txv is used.It is probably cap tube if it is a five ton. You can eliminate pressure safties and freeze stat if the pressures and superheat are normal. If it is not econimizing at low ambient it could be the freeze stat. Solution is head pressure fan cycling. This will keep your head up which will keep your suction up above freezing (saturated in evap). I like adjustable pressure control. Cycling the fan between 225#-270# for R-22. If all is well and if there is a lock out relay try the tatle tales. If it still locks out and the tatle tale does not flag, it may be a safty switch glitching. A glitch is switch that is faulty, it opens so fast that the lockout relay locks the unit out before the tatle tale flags. If this happens you can put a delay on break timer across the lockout relay coil. This will keep lockout relay out of the circuit for 30 seconds. Eventually the faulty switch will fail.
To answer your question about the remote mounted potentiometer. You probably saw that on the schematic as an option. It would be field installed down in the space being tempered. More than likely you have the potentiometer on the honeywell 7459 econimizer control under your filter grill. As to what that ice cube relay or combustion motor relay was. When you look at the schematic it will give you conrol component location on panel,(contactors, relays, sequencers,boards, ect) This helps to identify controls.
11-11-2006, 01:22 PM
Next time, take more readings.
OD and ID ambients
Pressures and temps, subcool and superheat.
Does it lock out while your there.
Does it have an economizer.
11-12-2006, 08:19 PM
I'm not sure I understand all the terminology in your first post. I like your idea about "a freeze stat problem if not economizing." I will check that. None of the units so far have a TXV. 5-30 ton.
Is "head pressure fan cycling" a method of turning the condenser fan off within a pressure range? I believe there is another technician in this area that subscribes to your technique. I have found several units retro-fitted with pressure/electric control devices, but have not spent much time thinking about them in fear of confusing myself even more. I always look for the obvious and familiar first. However, I appreciate you bringing this up. It will help me in the future.
The initial unit that keeps turning off after a few minutes has had the Furnace section gutted. I learned this last week when we had some cool weather. I suspect a cooling circuit issue that the previous technician did not secure when disabling the furnace. I have not had time to track it down with so many other pressing issues.
Allow me to address an issue beyond the unit I initially wrote about:
I have several others of this York Model that run fine, but at some point they lock out, and the disconnect breaker on the unit must be reset to get it to turn on. This is usually a morning issue. We are still having some warm days down here. If it is warm out, and the unit is not on, more often than not the unit will come on if I cycle the breaker. I am beginning to suspect a common faulty part. I will be calling York Tech Support next time it is feasible.
If anyone knows why this could be a widespread issue, it may save me some time. I am in your debt, and you are in my gratitude.
Thanks a million guys.
11-13-2006, 11:14 AM
Your problem will require some time and a few electrical meters to actually stand and watch the unit while running and methodically work your way throught the controls to detemine which one actually is opening. The remote potentiometer can be located anywhere within the building, sometimes in a convenient location near the make up air controls,etc near a grill or something but sometimes it is hidden in a secure area like a locked office so staff can't tamper at will. The secondary high limit is usually located on the fan shroud above the burners somewhere. You will probably have to take the top off to find it but you should be able to prove with a meter if this control is faulty just be metering out wire connections in the electrical section first.
You say unit shuts off. I am not sure if you mean cooling. Is the evap fan operating when you think it shuts off. I am not sure if these units have a lockout relay or lockout board. What is the model number? I don't know how these units are controled. Simple t-stats or DDC, ect. If simple thermostats you need to use a meter and see if you are getting 24vac at Y1. Y1 is the first stage cooling signal from the thermostat. Look where your stat wire connects to the board on the york unit. If you say unit is shutting off, before you reset the unit from the disconnect place your meter on Y1 and a 24vac common terminal. This will tell you if you are receiving a signal from the stat. You must start with the basics when troubleshooting. Troubleshooting 101 is knowing the sequence of operation of the unit. Then ask yourself do I have line voltage? Do I have a call from the thermostat (cooling,heating,fan). Cooling call will be at Y1 terminal on board. Heating will be at W1. Fan will be at G. You may be getting a cool call and the unit is econimizing without you knowing. Remember if you have an econimizer your cool call goes through it before mechanical cooling. You may have a problem with the economizer which is locking out mechanical. Head pressure fan cycling is what you said. It is actualy is termed low ambient kit which includes pressure sensing control to cycle fan in a desired range and also a crankcase heater to keep liquid from migrating to compressor durring off cycle. I hope this clears some things up. Good luck
11-15-2006, 07:38 PM
M/N: D4GC060N08225 MAC
I never thought about the economizer running in low ambient conditions. Thanks for the suggestion. That just may be the issue. As I stated before, I am much more familiar with split systems under 5 tons (mostly residential. I will do the obvious as you suggested: check the T-Stat before cycling the breaker, and then check the Evap fan for economizer cooling. That makes more sense than anything. Now all I need is a day near 80F. I appreciate everyone's assistance. All of you have given me much to work with.
11-15-2006, 08:12 PM
I would check what area the unit is cooling and what the t-stat temp is set to, if it runs all night due to low setpoint it might lock out on the feeze-stat
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