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Carrier rooftop unit high had preasure!!! Please help

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#23 ·
Could you tell me if the air blows straight up out of the fans, or if it comes off the fan blade tips?

This is with all the panels in place.....
 
Discussion starter · #24 ·
Seems to blow more out the sides than straight. I am starting to think that with the condenser coil being so beat up, maybe that's my problem....
 
#25 ·
I would check the hpco's as well. Last one I worked on had 3 condenser fans. As mentioned before, a cap for the middle fan was bad, causing the middle fan to run backwards. But, mine tripped on hpco, I think around 450. If the hpco's are disconnected or not there, I would add them. Lpco's too if needed. They're cheap insurance.
 
#27 ·
Hutch1 said:
Seems to blow more out the sides than straight. I am starting to think that with the condenser coil being so beat up, maybe that's my problem....
Click to expand...
I think you will find it is a combination of two conditions.

1) bent fins.

2) dirt embedded in the slab coil.

If we could look omnisciently into the history of this unit from 2007 to present, I doubt that we would see any record of a good coil cleaning. A few sprays with a hose...maybe even a washer...but a real cleaning? Probably not.
 
#28 ·
run one fan at a time and note the rotation. Spray the condenser with a hose and see if the high side runs closer to normal. I went thru this with a Trqane years ago..thought the condenser was clean. I cleaned it also. Still had a problem. On a whim, I used the Nu calgon blue Bright and lots of water. I finally used a RTI foam adaptor and forced water thru the condenser coil. That solved the problem.
 
Discussion starter · #30 ·
Thanks again for all your guys help. I haven't been back, but I will check everything that has been mentioned and let you know what happens. Again, thank you it's nice to know there are guys out there willing tof help.
 
#31 ·
Sometimes, I learn as much as the guys we help. Maybe not in the same way, but being able to look over a dozen or so shoulders every day teaches me how other techs think, and how I can improve myself, as well.

Just let us know how it plays out by posting back in this thread. Thanks.
 
#32 ·
timebuilder said:
Sometimes, I learn as much as the guys we help. Maybe not in the same way, but being able to look over a dozen or so shoulders every day teaches me how other techs think, and how I can improve myself, as well.

Just let us know how it plays out by posting back in this thread. Thanks.
Click to expand...

yea i find reading about other guys problems jobs really help when you run into your own..
 
Discussion starter · #35 ·
Well..I am going to have to say it is ac combination of things that are causing the problem. Dirty coil that I thought I had clean, bent fins and a bad design by Carrier. So, after a lot of cleaning and reducing my charge it is finally running normal. Thanks again for all the input!
 
#36 ·
Throw some water on the condenser coil see if the head drops. If so that should give you some idea of what might be going on.


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#37 ·
Hutch1 said:
Well..I am going to have to say it is ac combination of things that are causing the problem. Dirty coil that I thought I had clean, bent fins and a bad design by Carrier. So, after a lot of cleaning and reducing my charge it is finally running normal. Thanks again for all the input!
Click to expand...
If you had to remove refrigerant to get the pressures normal, you still have a problem. Did you ever check rotation of the condenser fans. You should also check the placement of the fan blades, they could be too high or too low in the shroud. What micron level did you get when evacuating, could have non-condensables in the circuit.
 
#38 ·
I will add one thing, and that is concerning the design flaw of this particular model...TB eluded to it, too.

If you track the discharge pipes from the compressors to the condenser coil and the liquid lines leaving, you will find that the upper half of the condenser coil is for one stage while the bottom half of the coil is for the other stage.

90% of the time the stage of cooling that is tripping on the HPCO and ultimately being locked out by the CLO device is going to be the stage utilizing the top half of the coil. The lock-outs are more prevalent on those hotter than average days.

Carrier has yet to say anything, but it becomes pretty obvious when you walk up to one of these units, is that the heat rejecting air coming off of the condenser fan motors is being recirculated into the upper 2 or 3 inches of the upper section of the condenser coil. Get into the upper 90 and even 100 degree temps and this ultimately wreaks havoc by driving the head pressure up and ultimately locking out that compressor associated with the upper section of this coil.

I know this was an issue, since earlier models the condenser fan motors laid flat along the top and later models they mystically are installed at a 45 degree angle in an attempt to jettison the hot air away from the condenser coil. But this does not always work based on prevailing winds and other scenarios, still may see recirculation.

So keep this in mind. Put your hand right at the top edge of the unit where the upper section of the condenser coil meets the sheetmetal, if your feeling hotter than ambient air, be assured that your re-circulating that air into that upper section of the coil.

This is the design issue side of the units. I have multiple units that the fan motors are installed flat and not at a 45 angle. I have done everything in my power from cleaning the coils until the cows come home to playing with fan pitches, in any case as soon as it gets to about 98 to 100+ degrees, I am dealing with nuisance lock-outs on the upper half condenser coil stage of cooling.

IF AFTER VERIFYING EVERYTHING IS GOOD MECHANICALLY, COILS ARE CLEAN, REFRIGERANT CIRCUIT IS GOOD, well.......

Remedy, measure the full length of the top of that unit above the coil. Cut a piece of heavy gauge sheet metal to that length by 8" wide. Place a 45 degree 1" fold along one side of that length and carefully screw that down along the sheet metal top edge above the coil. This acts like a baffle that sweeps that hot air up and away from the coil and prevents re-circulation. This has resolved 90% of my compressor lock-outs that seem to happen only during HIGH outdoor ambient conditions.
 
#39 ·
Did you use a flared filter drier? Known of a tech or two that has had a problem brazing in a new drier into a Carrier because it is way in behind and over the compressor. You could get a little too much “phison” into the joint and then there is a restriction. Kinda hard to find out because you have to have the panel off to feel the outlet of the drier to see if it might be cold but then you might not feel a temp drop anyway. I have already been chewed up on this once but start back at the beginning, what have you changed and what would cause the immediate increase in head pressure that you are seeing?
 
#40 ·
I have actually seen SLC's fix implemented on a roof near me. It is a problem that is aggravated by that lack of a clean coil, which forces the radial discharge (out the ends of the fans) of air, which puts that hot air an inch from the top of the coli...where it is easily drawn back in.

The 48xxx014 and similar units can do the same thing as they too can suffer from a prop stall just a inch or so away from the top of the coil.
 
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timebuilder
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