AC will not shut down

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john999

Hello all...hope someone can help me out here. This unit is in a 1980's mobile home. Coleman Pres2 7655-856 with 5 year old Trane Cumberland compressor outside. The AC stays on (inside blower and outside compressor) blowing cold. I've separated and connected the wires (red-white) from the 2 wire factory Coleman Thermostat with no change. Can only be shutdown at the panel (both stop) ...and both come on when the panel is switched on.
Lines are not frozen...and the contactor outside (Trane) seems to be working and not "fused" together...with power off, I can move the contacts in the spring-loaded switch...if that's the test for it.
The 2 switch unit is switched on "Auto" and "Cool" at the selector. When switched to heat , the unit does turn off (both inside and outside fans/blowers)...when changed back...both come back on.
I replaced the 5 blade blower relay, no fix. Could this be the transformer? how to test?...Sequencer?....help....thanks in advance !, john
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Robert
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Posts: 6413
Joined: Wed Feb 28, 2007 12:07 am
Location: Tennessee

Hi John,

Does it do this with t-stat set to HEAT and the furnace switches set to COOL and AUTO ?


That is the correct settings for a 2 wire system for a/c mode.


If you set t-stat to COOL, it will run continously.



Will check back later tonight, can definately help ya and have the needed parts.


Thanks,
Robert
Some people are Humbly Grateful, while some are Grumbly Hateful.................... Which one are you ?
john999

Hi Robert...the AC runs with it all the way to the top (90 degrees) and all the way to the bottom. The type thermostat on this older system only has the "slider" from 50-90. I disconnected the T-stat and tested it with a multitester...it sounded when switched. Then took the wires and tied them together as well as separated, no change...AC still running away. Oddly enough...I could've sworn it used to "spark" when it contacted. Should I check for voltage to the thermostat?...better yet...how do I check for voltage? One wire is red, the other white...really isnt a ground here is it?
Hope to hear from ya soon !
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Robert
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Posts: 6413
Joined: Wed Feb 28, 2007 12:07 am
Location: Tennessee

At the furnace where the switches are, HEAT-OFF-COOL and FAN-ON-AUTO, that is your a/c control box.


Can you locate a model number on it, it could be in front, the sides or back ?


This is ~most likely~ going to be a faulty t-stat reversing relay that is located inside the a/c control box.


Will need the control box model number if possible. May can get it from using the furnace model number in our database.


Thanks,
Robert
Some people are Humbly Grateful, while some are Grumbly Hateful.................... Which one are you ?
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Robert
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Posts: 6413
Joined: Wed Feb 28, 2007 12:07 am
Location: Tennessee

Just wanted to add that 2 wire systems are different from all others. The wall t-stat will stop it and start it, but it is ultimately controlled by the t-stat reversing relay.


The red and white wires at t-stat should read 24vac across them with a/c running.


Should show 0vac when a/c should be off.



Thanks,
Robert
Some people are Humbly Grateful, while some are Grumbly Hateful.................... Which one are you ?
john999

Hi Robert...sending some pics of the system.ImageImageImageImage

The Green 1,2,3 are where I got voltages of 16.57---4.54---16.61vac in that order.
I included a pic of the wall t-stat, no idea how to test it...cant get a reading from it...do I ground one end of the multitester and check the red then white for voltage?
The green circled relay is the one I replaced before the very first e-mail, no fix.
Last is the arrow of the system switch i'm using to start/stop the AC unit.
Is the reversing relay you're talking about to the right of the relay I replaced?
The box itself doesn't have a number, but the rev-relay does...alot of them. 12510...304982...H24v...7670-307...H25 55...C15-45...L9114. Hope this helps !!!
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Robert
Moderator
Posts: 6413
Joined: Wed Feb 28, 2007 12:07 am
Location: Tennessee

Hi John,

Set the switches on front of control box to COOL and AUTO.


Then set t-stat to where you want room to be as for as temp goes.


IF your t-stat has a mode selector, set it to HEAT.


Let the a/c come on and run.


If you remove the cover to t-stat and place one meter lead on red connection and other meter lead on white connection at t-stat, you should read 24vac.


WHEN it is correct temp in home for a/c to shut down, you should suddenly read 0vac across those same t-stat connections.


When it reads 0vac, IF the a/c continues to run, it is most likely stuck contacts on the reversing relay.


Yes, the rev. relay is beside the blower relay you replaced.


It can be seen and ordered from here:


http://www.mobilehomerepair.com/ColemanAC.html


Scroll down right side to locate, click on pic for enlarged view.



T-Stat Reversing Relay # 7670-3071 @ $25.07 + $6.75 shipping .



If interested, please add to cart and order through PayPal or

call toll free to 1-877-263-7860 and charge to Visa or Mastercard.



Thanks.


I will be off here until Tuesday of next week due to death in family and out of state trip.



Take care and best wishes,
Robert
Some people are Humbly Grateful, while some are Grumbly Hateful.................... Which one are you ?
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