Fan speed & water trap questions

[Steve R]

I know there is supposed to be a 3" P trap on evaporator line, is that so air blowing around the evaporator coil doesn't blow out that line? Basically what is the purpose of it? I know in drain side it is to keep sewer gases out but if you are not connected into the drain system, just having it drain into a floor drain which already has the P trap.

I had my system up and running today in my garage. I got the condenser and evaporator and had to come up with my own blower.
Condenser = Carrier 38CKC042300
N-coil = Carrier CK5BXA042021AAAA
Blower is from a Goodman GMPN080-4 furnace that I dismantled the heating part and used blower and part of housing.

I mounted the blower on top of evaporator housing with 17" of open air chamber between blower outlet and coil. No duct work other then between blower and evaporator. Mounted air filter on side of blower housing where the return duct work originally attached (20"X14") and it tries to **** the filter in there. The bottom of the evaporator is open for right now. I have it mounted to the side of my loft in the garage so the bottom of the evaporator housing is 9' above the floor. I planned on mounting a small duct to the bottom to kick the air out instead of down. Yes I'm pushing air down through evaporator.

The evaporator is getting cold but the air coming out is not much of a drop, just couple degrees. 85' going in and about 83-82' coming out. Water running out drain line with a steady stream. I tried choosing different blower speeds (switching wires) but it did not make much difference. I did restrict the air flow by closing up the how for drawing in air. That help and dropped the outlet air to 72' with 85 going in.

With not duct work there is no restriction and it move ALOT of air. Can I just restrict the inlet opening and slow amount of going through or should l look for a different blower? Any other thoughts on this??

This evening when the ambent temp outside as 84' the low side was 72 psi which shows about 43' and high side was 233 psi which shows about 113'

Thanks

 

[fitter30]

When coil is on the suction side of the blower the condensate line is in a negative. To over come the suction a trap close to coil is needed. To know how deep the trap has to be the negative pressure can be measured with a inches manometer. The trap has to be deeper the pressure reading and if it's deeper it will work just fine also it will compensate if the filter gets filthy. When piping a trap make it so it can be taken apart for cleaning. Coils on the pos side of a blower don't need to trapped the air will blow the con out.

 

[fitter30]

Assume refrigerant 22 by the pressures metering device expansion valve, orfice or cap tube? Your short of gas. 57 lbs = 32° you should be around 65 lbs suction.

 

[Steve R]

Yes it is R22 but my low side was 72 lbs. not 57. I'm ging to try and get my bottom duct work done and see if that will help with the cooling. Put a little back pressure of air against the coil.

 

[Wrench97]

When coil is on the suction side of the blower the condensate line is in a negative. To over come the suction a trap close to coil is needed. To know how deep the trap has to be the negative pressure can be measured with a inches manometer. The trap has to be deeper the pressure reading and if it's deeper it will work just fine also it will compensate if the filter gets filthy. When piping a trap make it so it can be taken apart for cleaning. Coils on the pos side of a blower don't need to trapped the air will blow the con out.

And I heard the trap was to keep bugs out..................................

 

[metlmunchr]

Having the fan blowing straight at the coil with no restriction in between is a bad arrangement. The velocity pressure component is blowing the bulk of the air thru a relatively small area of the coil, hence the small delta T. The regular stream of condensate is coming from the remainder of the air which is passing thru the coil at something nearer to the proper velocity.

Choking off the fan inlet probably won't help much as it won't affect the downstream resistance. It would be better to block off the discharge past the coil, but there's no guarantee that will work. Pretty easy to do though with cardboard and duct tape. The design of the fan wheel in a residential blower keeps it from overloading due to a restricted discharge. But, handling too much air due to a lack of external static pressure (same as a lack of restriction) will cause overload and lead to short motor life.

The real way to correct your problem is to reverse the order of the coil and blower. IOW, have the blower drawing air thru the coil. This is the way virtually all fan coil units are arranged, and that arrangement is to avoid exactly the problem you've got.

A furnace with an A or N coil is usually arranged as a blow thru. But there's a heat exchanger between the blower and coil, and that acts as a baffled plenum to prevent the air from having a straight shot from blower to coil. The simplest way to use the equipment you had would've been to leave the furnace intact with the heating section disabled and mount the coil to the discharge end of the furnace.

That coil uses a fixed orifice rather than a TXV. The system has to be charged via superheat rather than by trying to judge the charge by suction pressure. Charging via suction pressure will lead to overcharging most every time on a fixed orifice system. However, until you get the current air flow problem resolved, there's no way to tell what the state of the charge is.

 

[PoorUB]

I would recommend pulling the air through the coil first, then through the blower. You get more even air flow through the coil.

When I sold HVAC equipment I sold a blower unit and cased A-coil to a contractor. He installed it and called to complain it didn't cool very well. I found out he mounted the blower to the coil so it was blowing air through the coil instead of drawing the air through. He took it apart and reconfigured it so the air flowed through the coil, then through the blower and it worked fine.

Also, whan you connect duct to the outely of the blower, you should transition the duct from the size of the blower outlet to the size of the duct required. So think of a "V" shaped duct with the small end of the V connected to the outlet of the blower. It smooths out the airflow and you will be able to run at a lower blower speed.

 

[fitter30]

This ahu doesn't have a muilti speed blower? Suction line sweating?

 

[Steve R]

The motor has 4 wires and they are on terminals neutral, cool, heat, motor 1. I tried all 3 wire with the bottom of evaporator open and it didn't seem to make any difference between them.

I did get a bottom cover made and installed. The bottom is 14" from the bottom of the evaporator. Right now I have 2 of 8" x 14" holes cut into the side for air to come out, no grills or screens at this time, just open holes. I have 83' air going in and 50' - 51' coming out.

The suction line outside at the condenser is sweating. I have it insulated from the evaporator to within 1 1/2" of the valve/port. I have not checked pressures running like this.

 

[Steve R]

I went and done some testing today. After about 20 minutes of run time
Wet bulb temp was 65.7' F (incoming air)
Dry bulb (outside by condenser) 92.5' F
Lo side gauge temp (not psi) showed 42' F
Temp of return line about 3" from service valve on condenser showed 52.4' F

From what I can find this is pretty close to where it should be. Can anyone verify this?

Thanks

 

[metlmunchr]

Download an app called checkcharge. Free. You can select refrigerant type, enter target superheat or it will estimate it based on type of refrigerant. Enter inside WB, outside DB, suction line pressure and temp at outdoor unit. App will tell you state of charge, over, under, or correct. Works well and easy to use.

 

[Steve R]

That app works pretty good. Plugged all the numbers in there from above and rerun the checks again and everything came out ok. Thanks for the help.