Poor Cooling

[tecchris]

Hello everyone,

I am having an issue with cooling in my house. The unit constantly runs and can't cool the house any lower then 71 deg when it is around 85F outside amb. If it cools outside (say around 75f) the unit will bring the inside amb to around 68. Thats it. I am somewhat experienced with Hvac system, but mostly with automotive HVAC systems. I have done some research and monitored my system and this is what i have so far. Just not sure what the issue is. BTW i just purchased the house, so not sure how old the system is. It is a Fedders model # CKC030E7B 1.5 hp rev LB RLA=16.7 and LRA=63.8. R22 system. My readings are as follows after running approx 20min....

Suction 74psi---44f(R22) line temp 69f
Discharge 210psi--105f(R22) line temp 107f

Amb temp
outside---85f
Inside----73f

superheat= 15f
supercooling= -2f


My beliefs are the superheat is borderline low and the supercooling is very low. Thinking that the system is undercharged. Also sorry but i couldn't get the compressor load amps. My inductive clamp bit the dust. Any help would be appreciated. Thanks in Advance

[Panama]

69-44=15?????

[beenthere]

Paname, it the new math.


Whats your webulb.

[klyons20]

sound like the system is running like a kitty kat.. leave it a long. It is not under charged.. The fact that it runs all day if its 85 degree what do you expect..

regards,
Kelvin

[beenthere]

Kelvin, don't know about your area, but around here we size to maintain a 20° delta.

He's running all day to do 14°.

[websy]

supercooling -2F??????????

That would be subcooling and it would be 2F, definitely not a negative number. I would need to know a few more things but it sounds like you might be a little shy on refrigerant.

How much cooler do you need to be though???


-websy

[tecchris]

First off,,sorry for the typos. The superheat is 25f NOT 15. Websy, I thought if you Measure the surface temperature of the LIQUID LINE (107f) and subtract it from the gauge temperature (105f) or 105-107= -2f. Am i doing this wrong?. Also what else do you need to know? Beenthere---can you please explain further? 14delta???

[beenthere]

85 outdoor temp - 71 indoor temp = 14° temp difference(delta).

You subtract the line temp from the guage temp to get subcool.
In order to have a - subcool there would have to be a restriction in the liquid line before your probe, such as a factory liquid line filter.

Your probe may not be accrurate, or your guage is off.
Or low on charge.

[Edited by beenthere on 06-13-2005 at 05:32 AM]

[klyons20]

What is the square footage of your house?
Looks like that is a 2.5 ton unit.
What city are you in..

regards,
Kelvin

[tecchris]

Kylons20---The square is about 1500. I Am in New Jersey near the Hamilton area.

beenthere---i used two types of probes, one was a ir temp gauge and the other was the fluke thermocoupler. I attached the sensor wire to the pipe with a wiretie and let it sit there for about 10 min to stabilize. both were about 2-3 +/- from each other. I also compared readings with two different manifold gauges, Robinair- and Mac Tools. So do we think the system is low?

[beenthere]

Your subcool and superheat readings indicate low charge.

Is your air handler in the attic or basement.

Check what type of metering device you have.

Then check your delta across the coil, if less the 16°.

Adjust charge by superheat for piston, or subcool for txv.

If more then 16°, look for air leaks in your duct work.

[klyons20]

After paying more attention to your original post. I agree you are a little under charged. You low side should have been some where near 80.

regards,
kelvin

[tecchris]

My air handler is in the basement. How would I find out what kind of metering device I have? Is there a label or do i have to physically check in a certain area? Is there anyone that you know that will sell R22? I dont have a licence to buy for R22 (just 12 and 134a). I m running very low on the tank i had but may need more. THANK YOU EVERYONE FOR TAKING THE TIME TO HELP ME!

[heykiss]

tecchris, i think you're on the right track. it looks like you have the wrong piston size.there's no way you would have 74# suction and be low on gas with a return air of 73 deg. the piston is too large, not allowing liquid to back up into condenser for subcooling.install a t.x.v. and charge by subcooling (6-8 deg.) then set your superheat.but, make sure the t.x.v. is not commercial,must be for residential with off cycle bleed port.or,find out the correct piston for the cond. unit.

[beenthere]

To heykiss.

Alot of residentcial txv's are non bleed.

Next why only bribg the sub cool to 6 or 8°, and then adjust superheat?

Where talking a/c not walk in freezer.

[heykiss]

beenthere,6-8 deg. is my starting point,then set s.h.,then depending on seer (forgot to mention), i would add refrig. for 8-13 deg sub. because if it's only 85 deg. outdoor amb. i would worry about higher than normal head (causing higher amperage draw, killing eff.) when it got to 95 deg. amb. just my way of doing a piston to txv upgrade. thanks for the tip on resdential txv's not all having % of bleedport. i shouldn't rely too much on supplier info.

[tinknocker service tech]

i will be willing to bet this is an old fedders with cap tubes. the head seems a little low and super heat a little high should be between 12 and 15 degree superheat. your head may wind up arround 250. if my memmorie is correct about those old war dogs.