Author Topic: Heat Pump Defrosting  (Read 4928 times)

Offline Icehouse

  • Technician
  • Member Since: Oct 2008
  • Posts: 569
    • hvacbob
Heat Pump Defrosting
« on: December 26, 2008, 08:39:19 PM »
To clear some misunderstanding here is an excerpt from Wayne Shirley's (Heat Pump Specialist for RSES) book:
"With time-temperature controls the outdoor coil sensor switch is usually the first to go. These switches are simple bi-metal devices that clamp to the coil tubing. They suffer through wide temperature swings as well as lots of moisture, so it’s understandable that they could fail. And some of them, due to design, simply fall apart...I quite often see the “shell” still attached, while the guts of the device are lying in the bottom of the condenser....But with these sensors it’s usually a fairly simple procedure to check whether or not the switch is closed, either by measuring for continuity or voltage drop across the leads. And if it’s covered in frost or ice, it should be closed. If you need or want further evidence to eliminate the board, jumper across the sensor connections, in effect “closing” the switch, and then short across the defrost board test pins. If the control initiates a defrost cycle, the board should be good. Of course, if you find the switch apparently closed and jumpering the test pins fails to initiate a normal defrost cycle, you have to assume the board is faulty. Before doing that, switch the reversing valve with the control wiring or stat to eliminate a bad reversing valve, or valve solenoid."
NATE, NCCER, PHCC,HVAC Certified Instructor
Member RSES, US Army Refrigeration Specialist(Retired), Former Refrigeration Teacher NYC Board of Ed.
a tragedy has happen to me : http://web.me.com/zenzoidman/Bobice/

Offline JWWebster

  • Technician
  • Member Since: Jan 2008
  • Posts: 8780
  • Country: us
  • SublimeMasterJW
    • Buy me a beer through paypal
    • JW's Sublime Appliance Advice
Re: Heat Pump Defrosting
« Reply #1 on: December 26, 2008, 09:19:55 PM »
Damn it boy you is good!
May the hinges of our friendship
        never grow rusty.

About the icons: The beer is tip link, if a tech saves ya some money buy em a 6 pack. The small green square=personal message. The green dot is a link to my web page on appliance repair and other general BS I love to post. The letter sends me email.
I love fan letters! LOL

Offline JWWebster

  • Technician
  • Member Since: Jan 2008
  • Posts: 8780
  • Country: us
  • SublimeMasterJW
    • Buy me a beer through paypal
    • JW's Sublime Appliance Advice
Re: Heat Pump Defrosting
« Reply #2 on: December 26, 2008, 09:25:25 PM »
What does happen when the defrost takes place? I would think that the valve reverses for a minute and melts the ice. Just stopping the unit won't totally do the job so does the unit stop the fan but keep the compressor going AND reverse the valve to flood the unit with hot gas?
May the hinges of our friendship
        never grow rusty.

About the icons: The beer is tip link, if a tech saves ya some money buy em a 6 pack. The small green square=personal message. The green dot is a link to my web page on appliance repair and other general BS I love to post. The letter sends me email.
I love fan letters! LOL

Offline Icehouse

  • Technician
  • Member Since: Oct 2008
  • Posts: 569
    • hvacbob
Re: Heat Pump Defrosting
« Reply #3 on: December 27, 2008, 03:57:05 AM »
 :) Not me, Wayne Shirley
"During a defrost cycle three things take place...1) the reversing valve switches to the “cool” position 2) the outdoor fan de-energizes and 3) the control(s) energizes an Aux heat terminal (W)...Most of today’s equipment accomplishes all this from the “defrost board”. The board contains the necessary relays and contacts to turn stuff on or off. A few systems may use a separate relay to provide the switches, and the board simply energizes the relay coil. Many defrost boards include a time delay function for the compressor contactor, which has nothing to do with the defrost cycle control."  O0
NATE, NCCER, PHCC,HVAC Certified Instructor
Member RSES, US Army Refrigeration Specialist(Retired), Former Refrigeration Teacher NYC Board of Ed.
a tragedy has happen to me : http://web.me.com/zenzoidman/Bobice/

 

Heat Pump Electrical Componet Check

Started by Icehouse

Replies: 1
Views: 6922
Last post February 25, 2009, 08:00:45 AM
by thermodix
Goodman Company Reannounces Recall of Air Conditioner/Heat Pump Units

Started by AJ

Replies: 0
Views: 4809
Last post December 08, 2009, 03:52:04 PM
by AJ
Tempstar Heat Pump not running but Air handler is

Started by lgmccoy1

Replies: 4
Views: 5993
Last post November 19, 2010, 06:16:05 AM
by jumptrout51
Tempstar heat pump won't initiate defrost cycle

Started by lgmccoy1

Replies: 13
Views: 9794
Last post December 24, 2010, 12:53:31 PM
by jumptrout51
Carrier Heat pump OAT 25HPA

Started by chrissymustang

Replies: 4
Views: 5460
Last post February 02, 2011, 05:21:06 PM
by chrissymustang
Auxillary heat turns ON when the heat pump is providing heat

Started by JeanThomas

Replies: 8
Views: 5854
Last post March 30, 2011, 11:44:38 AM
by Icehouse