Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > HVAC

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 01-19-2010, 07:20 AM   #1
Member
 
Join Date: Dec 2008
Posts: 70
Rewards Points: 14
Share |
Default

O/D temp that triggers defrost


Noticed last night that my Lennox with demand went into defrost. It was about 40 deg o/d. Since it wasn't that cold the heat was cycling on/off as opposed to being constantly on. Is it normal to go in defrost mode at this temp? I thought it had to be closer to freezing.

jeepgrady is offline   Reply With Quote
Old 01-19-2010, 07:28 AM   #2
Member
 
Join Date: Jan 2010
Location: Acworth Georgia
Posts: 77
Rewards Points: 0
Default

O/D temp that triggers defrost


Yes they will defrost at 40, especially the older ones with the old 30, 60 timers. At 40 degrees the outdoor coil should be icing up. But it should take a while to ice up enough to hurt performance significantly.

H. Phillips is offline   Reply With Quote
Old 01-19-2010, 08:02 AM   #3
Member
 
Join Date: Dec 2008
Posts: 70
Rewards Points: 14
Default

O/D temp that triggers defrost


But as I stated, since the unit is cycling on/off, during the off period wouldn't the ice, if any melt? Since this is demand could there be enough buildup to trigger the defrost?
jeepgrady is offline   Reply With Quote
Old 01-19-2010, 08:35 AM   #4
Member
 
Join Date: Jan 2010
Location: Acworth Georgia
Posts: 77
Rewards Points: 0
Default

O/D temp that triggers defrost


The old standard defrost cycle was that a timer ran whenever the compressor runs, often selectable from 30 minutes up to about 90 minutes. Then if the suction end of the coil, the warmest end, is below 30 degrees then the unit ran defrost for a specific amount of time, say 10 minutes or till the outside coil reach's 60 degrees, thus a 30 - 60 timer. There are other methods which will reduce the frequency of defrost. The old method will often defrost when there is only a light coating of frost on the coil. One is to measure the air pressure between the fan and coil. As ice restricts air flow then the air pressure will drop. If it drops below a specified amount and the coil is below a specified temp it will then go into defrost. Newer systems use complicated digital controls that compute the ideal and most efficient time to defrost.
H. Phillips is offline   Reply With Quote
Old 01-19-2010, 09:48 AM   #5
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,073
Rewards Points: 42
Default

O/D temp that triggers defrost


Demand defrost will go into a defrost once every 6 hours of accumulated compressor run time to ensure oil return to the compressor. This helps to get a good life span from the compressor.
At what temp it will start to do this varies with each manufacturer. But generally, all of them can do it at 40F outdoor temp.

Also. At 40F, depending on the outdoor humidity. When its dark outside, and there is no radiant heat from sun light. Frost/ice doesn't melt real quick. And could build up enough to cause a defrost cycle.


Is your heat pump a 2 stage or single stage heat pump.
beenthere is online now   Reply With Quote
Old 01-19-2010, 10:31 AM   #6
Member
 
Join Date: Jan 2010
Location: Acworth Georgia
Posts: 77
Rewards Points: 0
Default

O/D temp that triggers defrost


He didn't say how old his unit is did he? How do you know he has demand defrost control?
H. Phillips is offline   Reply With Quote
Old 01-19-2010, 10:47 AM   #7
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,073
Rewards Points: 42
Default

O/D temp that triggers defrost


Quote:
Noticed last night that my Lennox with demand went into defrost.
I took this as meaning demand defrost.

Along with this.

Quote:
Since this is demand could there be enough buildup to trigger the defrost?
We'll have to wait and see what he says.
beenthere is online now   Reply With Quote
Old 01-19-2010, 11:09 AM   #8
Member
 
Join Date: Dec 2008
Posts: 70
Rewards Points: 14
Default

O/D temp that triggers defrost


It is three years old, two stage and, yes it's demand defrost, however, on previous colder nights it ran under a 45 min. time/temp mode which it defaults to if the board will not calibrate. I'm just trying to determine if this is normal operation or if there is a problem. There are led's on the defrost board and they are not reporting any problems.


With my original question relating to 40 deg. I don't know whether it ran for the six hours prior to defrost, which is the max time in demand mode prior to defrost, or the 45 minute time/temp cycle. I just happened to wake up around 3.:45 to take a wiss and heard it going into defrost.

Speaking of the six hours, as I mentioned it wasn't that cold and the system was cycling on/off. Does the six hours, or for that matter the default 45 minutes run time clock reset after the system turns off or does it accumulate the time?

Last edited by jeepgrady; 01-19-2010 at 11:54 AM.
jeepgrady is offline   Reply With Quote
Old 01-19-2010, 01:16 PM   #9
Member
 
Join Date: Jan 2010
Location: Acworth Georgia
Posts: 77
Rewards Points: 0
Default

O/D temp that triggers defrost


Quote:
Originally Posted by beenthere View Post
I took this as meaning demand defrost.

Along with this.



We'll have to wait and see what he says.
Ok. I guess I am to dense to understand if the word demand is not right next to the word defrost!
H. Phillips is offline   Reply With Quote
Old 01-19-2010, 01:29 PM   #10
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,073
Rewards Points: 42
Default

O/D temp that triggers defrost


Quote:
Originally Posted by H. Phillips View Post
Ok. I guess I am to dense to understand if the word demand is not right next to the word defrost!
Takes lots of practice.

Its easy to miss things like that.
beenthere is online now   Reply With Quote
Old 01-19-2010, 04:14 PM   #11
Member
 
Join Date: Dec 2008
Posts: 70
Rewards Points: 14
Default

O/D temp that triggers defrost


Any additional insight, please?
jeepgrady is offline   Reply With Quote
Old 01-19-2010, 04:21 PM   #12
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,073
Rewards Points: 42
Default

O/D temp that triggers defrost


See post #5.

Plus. if you post the model number of your heat pump. Then we know more about it to tell you.
Right now, we don't know if you have a single stage or 2 stage heat pump(2 stage compressor?).
beenthere is online now   Reply With Quote
Old 01-19-2010, 06:09 PM   #13
Member
 
Join Date: Dec 2008
Posts: 70
Rewards Points: 14
Default

O/D temp that triggers defrost


See post #8 where I state it's a two stage. It's a Lennox XP16.

Could you tell me whether the lag time in initiating defrrost whether it be the max on demand, 6 hours or in the example of my time/temp,scenario of 45 minutes, ( where the board did not calibrate) runs from cycle to cycle. In other words, let's say that the compressor runs for two hours non-stop. Then shuts off. When it starts up again does the timer just need another 4 hours of maximum run time to generate the defrost, or does the clock start at0 and then needs six more hours?
jeepgrady is offline   Reply With Quote
Old 01-19-2010, 06:19 PM   #14
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,073
Rewards Points: 42
Default

O/D temp that triggers defrost


Yep.

Its accumulated run time. It remembers how long it ran each time. And when it reaches 6 hours of Total accumulated compressor run time. It goes into defrost to make sure the outdoor coil is not oil logging.

On a calm windless 40 day, it could take 18 hours to reach 6 hours of compressor run time(might only run for 20 minutes out of every hour).
On a cloudy windy 40 day it might only take 12 hours(might have to run for 30 minutes out of every hour).
beenthere is online now   Reply With Quote
Old 01-19-2010, 06:23 PM   #15
Member
 
Join Date: Dec 2008
Posts: 70
Rewards Points: 14
Default

O/D temp that triggers defrost


So theoretically then, when mine went into defrost this morning the fact that it was 40 deg. may not even be part of the equation if the clock just happened to hit six hours since the last defrost at that time. Do you concur?


Last edited by jeepgrady; 01-19-2010 at 06:26 PM.
jeepgrady is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

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


Similar Threads
Thread Thread Starter Forum Replies Last Post
Help My Admiral Refrigerator is leaking water Cuwillis Appliances 10 03-25-2014 08:21 AM
GE Refrigerator doesn't hold temp martinia Appliances 2 12-30-2009 12:09 PM
Defrost in 40+ temps AndrewF HVAC 2 03-27-2009 02:10 PM
Best High Temp Paint for wood stove?? Sellncars Painting 9 01-21-2009 06:21 PM
Kenmore fridge not cooling, freezer ok bobvanhalder HVAC 7 10-22-2008 10:52 PM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.