Low air flow over coil???


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Old 07-09-08, 03:28 PM
J
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Angry Low air flow over coil???

Equipment:
Carrier Infinity T-stat
Carrier 3.5 ton coil CNPVP model
Carrier 3.5 ton 13 seer 24ACA comfort series with Puron
Carrier 58CV Variable Speed Induced-Combustion Deluxe 4-way multipoise furnace

Now to the issue at hand. The T-Stat came up with a warning that the filter needed to be changed so I went to look at it. The filter was fine but when I opened the coil it was frozen. I had a tech come out and give me some readings and here are those results.

Found the condensing unit has a 45 degree deltaT at the evap. 27degree superheat 78psi/43degree subcooling with 510 psi. The tstat was set to max air flow but was still not getting enough movement across the coil. The tech said it appeared the unit was trying to dehumidify and was when the outside unit came on the inside furnace went down. They suggested contacting an infinty specialist. Any insight would be great. I am in Georgia with current temps in the mid 80's to 90's. I will set the tstat to 78 and the house make its way up to 83. I also have 20% window film to cut down on the sunlight.
 
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Old 07-09-08, 04:10 PM
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Full model numbers would help here.

There is an evap freeze stat accessory for this setup.

45 Delata T is high pointing to low air flow.

However, 27 superheat and 43 subcooling point to low charge which would freeze evap with normal air flow.

I wanted to look at all info for your system, Carrier site is very slooow tonight.

Would like to see the stat model number or liteature number from the manual.

"Contact an Infinity Expert"?

Contact a tech who is not too lazy to educate his/her self about 410a.

At this point I'd say your low on refrigerant. But would also like to research a bit as far as the unit being able to dehumidify.
 
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Old 07-09-08, 04:28 PM
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The refrigerant is charged properly. The tech said even a chance of an over charge.

TStat=Carrier Infinity Control SYSTXCCUID01-B

COIL=CNPVP4821A(C,T)A---NOT SURE IF TIN PLATED COPPER

A/C UNIT=CARRIER 24ACA comfort series A/C with Puron 3 1/2 TON 13 SEER

FURNACE=CARRIER 58CVA/CVX

One more bit of info....The original unit in the house was a 3 ton and I upgraded to 3 1/2 ton. I was told by the company I got the unit from that there could be a return issue if the coil isnt getting enough air flow going over it. Keep in mind i bought the unit from a wholeseller and had a sub install the unit. The air coming across the unit gets so cold at times the duct work leaving the unit has condensation dripping off of it.
 
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Old 07-09-08, 05:33 PM
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After looking over the install manuals for all of your system components, I'm starting to thinh undercharge.

No, I do not care what your tech said at this point.

On the outdoor unit nameplate there should be a requierd subcooling line. What is the number? I'd guess 10 or 12 degrees.

43 is just way too high.

Also check if the furnace and tstat are set up correctly. Do you have the install manuals?
 
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Old 07-13-08, 02:47 PM
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Pressures...

You Said: R410a - "27degree superheat 78psi/43degree subcooling with 510 psi. @ mid 80's to 90's. "

*Sounds like a bad expansion valve/restriction/ with an overcharge - Or wrong refrigerant /mixed refrigerant/Air in system. Anyone agree?

*I would expect 150/300 - 165/335 @ normal various U.S. OD temps and providing all Coils are clean.
 

Last edited by The Real Deal; 07-13-08 at 03:08 PM.
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Old 07-13-08, 02:54 PM
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Those sc and sh readings do NOT point to an undercharge. 40+ subcooling tells me either a large overcharge causing far too much liquid in the outdoor unit, or as stated earlier a bad metering device, in this case a TXV causing liquid to back up in the outdoor unit. This would also be the cause of high superheat. The txv in the indoor coil has likely shut down. Was the variable speed control board set up properly (during the install)? Just an afterthought and in no way is the setup responsible for those numbers.
 
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Old 07-13-08, 02:57 PM
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Thank you!

My exact thoughts as posted - I lean more to a bad expansion valve AND it is overcharged by the tech trying to figure it out

This because of the "78"PSI - Expansion Valve starving the evaporator=bad valve - the suction PSI would be near normal 150 PSI ( Being resricted as it should be) if the valve were good, and it was souly overcharged - the discharge 510 shows the overcharge!
 

Last edited by The Real Deal; 07-13-08 at 03:32 PM.
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Old 07-20-08, 01:12 PM
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Problem almost solved!!!!

After giving up all hope on paid techs the in-laws came in down and just so happens the dad is an a/c tech up in Pitt. We got to reading the manual for the tstat(infinity/carrier) and noticed there is a setting for the size of a/c unit you have. When we got in the setup of the tstat it was programmed for a 1.5 ton unit and I have a 3.5 ton unit that solved part of the problem...this tstat can also check the cfm which was blowing at 1137. So we then took the cover off the furnace pressed in the button so the system would run. When doing this the CFM went up to 1400. So who thinks we need to add additional returns to the other side of the furnace to increase the return airflow with an extra return?
 
 

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