New AC not keeping up on HOT days

Reply

  #1  
Old 09-02-02, 03:44 PM
E
Member
Thread Starter
Join Date: Sep 2002
Location: Tennessee
Posts: 18
Received 0 Votes on 0 Posts
Angry New AC not keeping up on HOT days

I have a split AC unit. My old unit ran fine when it was charged up. It had a slow leak in the coil. Even on the hottest days it kept up and cycled on and off. I had a new AC unit installed in the spring. New Condensing unit, coil, and tubing. The new unit runs fine except on days when the outside temp is 90 or above. The AC runs non-stop until the sun goes down. The unit has been checked and the freon is fine. When the unit was intalled they did not use an evacuator to clear out the air. Would this cause my problem or should I look some where else? Also the air temp inside of the house is 57 comming out of the registers and 77 at the returns and I have the thermostat set at 76.
 
Sponsored Links
  #2  
Old 09-02-02, 04:00 PM
hvac4u's Avatar
Member
Join Date: Aug 2001
Location: NW atlanta
Posts: 3,147
Received 0 Votes on 0 Posts
20 degree

temp drop across the evap coil sounds very good, was a heat load done on the structure? is the equipment matched? if no vacuum was pulled, i would insist the installer reclaim the refrigerant, evacuate, and recharge the system.
 
  #3  
Old 09-02-02, 04:18 PM
E
Member
Thread Starter
Join Date: Sep 2002
Location: Tennessee
Posts: 18
Received 0 Votes on 0 Posts
All the contrators that gave me quotes said that I could just put in an AC unit and the heat/ air handler was ok. I have a 12 year old Rheem System and now I have a Goodman Condensing unit and an All Style "A" coil. Also My old coil was an "H" stlye. I am not sure if the differece in styles would make any difference. My old unit was a 3 ton and my new unit is a 3 ton. I looked up the specs on my coil it is a 36,000 BTU coil which is for a 3 ton unit. My new system was bought from Sears. No heat load was done on the structure.
 
  #4  
Old 09-02-02, 04:41 PM
Nominal
Visiting Guest
Posts: n/a
First, I would make them evacuate the systems and recharge using the superheat method. I'm sure this system has the piston metering device. I am not sure what an "H" style coil is. Does it stand for horizontal? is unit located in attic? or in a horizontal position somewhere? I would also check the duct where the new coil was installed. Make sure you are not losing any air. Check total duct system if possible. If duct system is in attic or under house, any air loss in supply causes a negitive pressure inside home. Air handler moves approximately 400 cfm per ton. If unit is putting out this much, it has to get it back. So, if air leaks are present in supply ducts, the return gets the air back from anywhere it can. It will pull air through cracks in the ceiling, floors, from around doors, etc., to make up the lost air. If this is happening, then it is possible the unit can't kept up with the load, even though there is a 20 degree temperature drop across the coil. So check for any air leaks in duct work.
 
  #5  
Old 09-02-02, 04:51 PM
Nominal
Visiting Guest
Posts: n/a
Forgot to ask. Does system feel like its moving the same amount of air? It may be possible that new coil is restricting some of the air flow, depending on how it was installed. Again if air movement is less than it was, maybe there is not enough air flow coming out to properly cool or keep up with the heat.
 
  #6  
Old 09-02-02, 05:46 PM
E
Member
Thread Starter
Join Date: Sep 2002
Location: Tennessee
Posts: 18
Received 0 Votes on 0 Posts
Yes it is a horizonal system. And I do think that the "H" is for Horizonal. The old coil was just one big block. I have sealed all ducts that I can reach. The air handler/ heater is in my attic of my attached garage (uninsulated attic). And the duct work is worked between the ceiling of the first story (all finished) and the floor the the second story. The only part of the duct work I can access is first 3 feet of the output and all of the return. I have made sure that all of what I can reach is sealed. I am not sure if the air flow is different. The new system was installed in April. (the heat was off and the AC did not get used until June.) So I did not get a direct comparison when the unit was installed. This did concern me when I went from a large "H" coil to a small compact "A" coil. The installers had to do some "rigging" to hook the two units together. My air handler is 14 inches wide and 24 inches tall. The new coil is 22 inches wide and 14 inches tall. (and no it can not be turned the other way) They also used the same sheet metal from the air handler and old 24 inch by 24 inch "H" coil. They just bent and blocked off certain parts. Then taped and insulated.
 
  #7  
Old 09-02-02, 05:53 PM
E
Member
Thread Starter
Join Date: Sep 2002
Location: Tennessee
Posts: 18
Received 0 Votes on 0 Posts
Is there a way to measure air flow into and out of a system?
 
  #8  
Old 09-02-02, 06:28 PM
Nominal
Visiting Guest
Posts: n/a
Yes there are tools that will measure air flow, but they are expensive. The horizontal coil that was taking out could have been bigger than 3 tons. If it was bigger, matched with a 3 ton condenser, it would have given you more cooling. Also it would have removed humidity better. Although we don't have the model # of the old coil. The only thing a can suggest, is to have a load test done. I believe someone mentioned where you can do this yourself. It was in the post titled "Heat Pump Sizing". Good luck.
 
  #9  
Old 09-02-02, 06:50 PM
E
Member
Thread Starter
Join Date: Sep 2002
Location: Tennessee
Posts: 18
Received 0 Votes on 0 Posts
Thank you, thank you! You just sparked my memory. I did write down the old Model numbers of the old system. The old condensor is RACC-036JAS and the Coil was RCAH-Z037S. This tells me that the condensor was a 36,000 BTU (3 ton) and the coil was a 37,000 BTU (3.5 ton). Correct me if I am wrong I have no way of double checking these numbers.
 
  #10  
Old 09-02-02, 07:11 PM
Nominal
Visiting Guest
Posts: n/a
A 3.5 ton would be closer to 42,000 btu's. It appears that it was a matched system. However back then the coils were bigger producing a little more cooling. I would get the load on the house done. However let me ask some more questions. Has anything else in your house changed? Added more rooms? installed more glass? windows? skylights? anyone work in attic and disturbed insulation? is insulation still in good shape? Any attic fans that may have quit working? cut down any trees or got rid of any other shading especially around windows? Also did they change the thermostat? Carrier came out with a digital t-stat and put the room sensor in the back of the stat. If the hole in the wall behind the t-stat where the wire comes through is not sealed, it effects the temperature display. Heat comes down the wall and out the hole and causes a wrong temp. display. Check temp with another thermometer at t-stat and see if its close. Does it seem colder in the house than the t-stat displays? Have you added more heat producing appliances in the home. How many square feet (conditioned area only) is your home? A rule of thumb here in Jacksonville, Fl. is 1 ton per 500 square feet. However, a load should be done because two story homes only have attic for the second floor, and needs less to cool first floor. You mentioned ducts between floors, so it is difficult to use this rule of thumb method.
 
  #11  
Old 09-02-02, 07:33 PM
E
Member
Thread Starter
Join Date: Sep 2002
Location: Tennessee
Posts: 18
Received 0 Votes on 0 Posts
Would a 3 ton "H" coil give me better air flow than a 3 ton "A" coil?
There is no shade on the house. That has not changed. Insulation is the same and no new windows or doors. I installed a digital thermomter a year before I replaced my air conditioner. And I did know about the draft in the wall so I did install a piece of insulation in the hole behind the T-stat. I will look into the Heat Load Calc.
 
  #12  
Old 09-02-02, 07:34 PM
54regcab's Avatar
Member
Join Date: Jul 2002
Location: Oklahoma City
Posts: 661
Received 0 Votes on 0 Posts
Smile Electric bill

Are your electric bills reasonable ??
The unit SHOULD run full blast when it gets up into the 90's
 
  #13  
Old 09-02-02, 07:49 PM
E
Member
Thread Starter
Join Date: Sep 2002
Location: Tennessee
Posts: 18
Received 0 Votes on 0 Posts
With my old unit it would cycle on and off even on the hottest days. The cylces were longer during the hot mid days. But the unit would keep up. My new unit will run from 2pm to 9pm non stop on days that are above 90. and my last three electric bills have been my highest ever. The new unit I installed is a 13 SEER unit and the old was 12 years old so maybe and 8 SEER.
 
Reply
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: