TXV questions

Timco

New to AC. I was asked about a system where the coil was freezing every time it was run, within hours. Found a 4 ton coil, 5 ton condenser, 80K Amana, and 5 registers. Serious. So I am installing a TXV and a 3 ton or smaller condenser. Question is on the TXV it has an adapter nut to connect to the evap coil distribution nut directly, but do I remove the orifice from that evap coil distribution hub or leave that in there? I know it's function but not if I need it with the TXV. R-22 Coil is from 2004, great condition. Sticking with R-22.



Second, what fitting do I need to connect the capilary nut to the 3/4 suction line?



Thanks.   Tim

Techman

Just a few questions,

Hi Timco, Did you check with the mfrg about the rating of the evap coil? Most mfrg's have  double duty coil's.What is the 80k ? A furnace?What size are the 5 take-off's? The return? The main supply trunk? What is the capillary nut?Is that the external equalizer fitting?And that little thing in the evap coil inlet connection, is that a small round disk with a hole in the center of it?If ,yes, then again check with the mfrg to see if is supposed to be there. Most AC unit's do not use them,most refrigeration sysrems do use them . How big is the space being cooled? What were your pressurer readings? A 3/4" suction is not large enough for 5 tons {60k btu's}. O.K. your turn!

Timco

More info

After speaking with my rep, here's what he had to say. I have 5 registers servicing maybe 1000 sq' of space. Did not measure ducts sizes. 90k Amana furnasty. My rep has proposed a 1.5 ton condenser to use with my 4 ton coil and we add a TXV. The metering orifice will be removed, and he suggested using wire strippers to remove the shrader nut from the capillary tube and drill a hole in the suction line and braise the capillary right in directly. No ability to speak to manufacturer of coil, ICP. Register openings are 5x7 or 8 as I recall.

Ironman

Too Much Coil..

A 4 ton coil is too big for a 1.5 ton cond. unit. The surface area and internal volume must be proportional to the outdoor coil. The TXV is not going to overcome this.

The coil will absorb heat faster than the c.u. can reject it; your suction pressure will be too high; and it won't remove moisture properly - if at all.



Go with the right size coil.

Techman

Timco

I'm just guessing here , a 1 1/2 ton C.U. is not proper for that size room ,unless it's insulated real good.Wire stripers to get an S.A.E. off of the capillary? Watch out for a burr.And be careful about copper chips/flakes if you drill into the suction line for the external equalizer connection.Can you get a load estimate done? That will tell you a lot, then decide what's right.If you tell the customer the real story ,they will like you professionally, and that may/may not get you the job.Either way you go , you have to know what's proper to do first. We use Schrader wrot T's sometimes. 3/4 x 3/4 x 1/4 msae fittings ,other sizes also.

Timco

Job

I already have this account. It is in a mansion, insulated and built to every extreme detail and to the highest level that 1992 could conceive. This is for the guest area and flows into another zone. Owners have not been on site for 2 years now. Complaint was from property manager who noticed the evap coil turning into a giant block of ice within hours of being fired up. As mentioned, it had a 5 ton CU that had a leak and lost a lot of oil and was getting noisy besides the freeze ups. I also maintain the snow melt there.



The stripper and drill suggestion is apparently the norm here. I spoke to another guy at the counter after my rep suggested this. It braised in perfect. I already performed a line flush after.



As it was explained, each register is 100 cfm and there are 5. The 1.5 ton CU will do 600 cfm and is actually still a bit big but will work with the TXV. This from my rep at a popular supplier that rymes with John's bone. I appreciate the input. The goal is to make this fly with the existing coil and add a TXV. They pick their battles in a odd way and have a specific top end price they will put into this for whatever reason. The 5 ton CU was installed in '06 and they feel like enough has been put into this. You know the drill, I'm sure. Thanks!

Steve Bukosky_2

Not always so!

Ironman, I agree with you for the most part. However, be aware that Trane and American Standard require a 5 ton evaporator on all of their 20 seer two stage heat pumps. That means that the 3 ton model, which is 1-1/2 ton on first stage, is feeding into a five ton evaporator! However, the reason for this is for adequate refrigerant capacity during the heating cycle. Otherwise I adhere to a generalized rule of 1/2 ton under to 1 ton larger than the condensing unit when not following a coil match-up.

Ironman

Thanks Steve

I was referring to the situation in this post. And as you alluded to, the 20 seer Trane has a much larger outdoor coil as well, thus providing more of a balance of internal volume and surface area with the indoor coil. The indoor and outdoor fans also slow down on first stage to mach system capacity and provide proper de-humidification.