high velocity central air low pressure

[TheDuke]

seen one today highside was at 245 psig low side was 50 psig
outside temp 74f
temp off vents 56f return 73f
had a 3m air filter, pulled it nothing changed
pulled cover off Evap. looked in with temp gun not freezing up.
noticed had a screen after the evap about one inch in front of it, then the blower after that. horizontail unit.
when i pulled the 3m filter before the evap about 6 inches away i looked at that side with a flash lite looked little dirty not that bad but
bad enough i guess
also the cond little to.
what is up with these high velocity units i do not see them that much
have small 1 to 2 inch vents for air

[newoldtech]

I'm not familiar with "high velocity units". But from what your describing it sounds more like a restriction. Whats your superheat and subcooling? Coils could be dirty and unit undercharged. Take more mearurements and that should help isolate it.

[4l530]

Head pressure looks a little high. What condenser is it mated to? I might try to cover the condenser coil and see what the pressures do.
How much crud did the evaporator have?
Now all these high velocities I've seen have got a TXV and once in a while I'll see one with a suction pressure like this, I think it is the way the TXV responds to the higher volume of air, by clamping down. Because there is so much more air moving thru the coil than a regular system it picks up enough heat to keep from trying to freeze at a pressure like this---just my theory about it. Which come to think of it could also account for an elevated head pressure?

[TheDuke]

Condensor is a goodman CKL60-1
temp off suction line at cond was 48 to 58 with temp gun
think temp off high side line at condensor was 73 to 78

[Mr Bill]

Originally posted by TheDuke

temp off suction line at cond was 48 to 58 with temp gun


How do you get an accurate reading on the suction line with a temp. gun do you dry off the suction line? I have to use a clamp thermometer to feel good about my reading on the suction line just wondering.

[beenthere]

High Velocity systems move less air the a conventional system.

The older units always had vapor pressures lower then what you would expect on a conventional.

How many outlets does it have, the old systems wanted 5 FULL outlets per ton, new ones 6 FULL outlets per ton.

Check the static in the supply plenum, min is 1.1", max is 1.5".

[TheDuke]

How much crud did the evaporator have?
maybe 15 to 20 percent not much
this unit cooled a third floor and a second floor.
inside unit was on the top floor
this thing I think is a 2001
oki the suction pressure is always lower on these type systems.
you would think it would be higher?

[TheDuke]

guess I need to read up on this type system
seen like two of them this summer out of the 200+ calls i did so fare this summer and both systems had low pressure on the suction side.
is there a website I can go to to get some good info. on them
thanks

[coolwhip]

Unico HV systems will generally run about 10 - 15 psi lower on the suction side than a conventional system.

ie: A normal suction for a unico system will be 65 psig with an 85-95 outdoor temp.

[beenthere]

Find a distributor in your area, they should be able to arange a seminar on them.

You should get about a 26 to 28° split at the A/H.
Thats why they have better SHR then most conventional unnits.

[spotts]

Originally posted by TheDuke
guess I need to read up on this type system
seen like two of them this summer out of the 200+ calls i did so fare this summer and both systems had low pressure on the suction side.
is there a website I can go to to get some good info. on them
thanks

unico.com

[ascj]

Im very familiar with Unico systems.

1) They with run a lower suction pressure and evap coil temp.

2) You are only moving 200 cfm per ton compared to 400 cfm

3) There are freeze stats on the units. (They have to be fielded wire, alot of installers forget)

4) I find alot of overcharged system. The installer adds gas to get suction up. The best way to charge is go by subcooling or approach, depending on manufacture.

I have worked on SpacePak and HiV systems also. Most of the info is the same.

[4l530]

Originally posted by beenthere
High Velocity systems move less air the a conventional system.

The older units always had vapor pressures lower then what you would expect on a conventional.

How many outlets does it have, the old systems wanted 5 FULL outlets per ton, new ones 6 FULL outlets per ton.

Check the static in the supply plenum, min is 1.1", max is 1.5".
I had always thought these systems were higher volume, being that it is higher velocity. Thanks for setting me straight on this. :cool:

[beenthere]

Originally posted by 4l530

Originally posted by beenthere

I had always thought these systems were higher volume, being that it is higher velocity. Thanks for setting me straight on this. :cool:


Its a common misconception alot of people have that don't install and or work on them very often.

[4l530]

Originally posted by beenthere

Originally posted by 4l530

Originally posted by beenthere

I had always thought these systems were higher volume, being that it is higher velocity. Thanks for setting me straight on this. :cool:


Its a common misconception alot of people have that don't install and or work on them very often.

I notice that the squirrel cage on these is a lot smaller than typical, is this then how they achieve the lower volume, and run it at a higher RPM for higher velocity?

[beenthere]

The size of the plenum, and supply runs allow it to have a high static, and the higher RPM blower and higher horse power motor to work against the high static.

Next time you work on one, look how thick that coil is.

[re2ell]

Originally posted by TheDuke
guess I need to read up on this type system
seen like two of them this summer out of the 200+ calls i did so fare this summer and both systems had low pressure on the suction side.
is there a website I can go to to get some good info. on them
thanks

here's another 2 sites for you get additional info on sdhv systems

http://www.eere.energy.gov/buildings/appliance_standards/residential/pdfs/sdhv_pres_final.pdf

http://www.miniduct.com/

[Edited by re2ell on 07-09-2006 at 10:04 AM]