Coleman evcon blower continues to run with switch in cool

[mldman75]

I have a 2-wire A/C control box # 7900A6021 running a coleman evcon presidential furnace system. When I switched to cool this spring the blower automatically kicked on and so did the outside A/C unit. As long as the Heat/cool switch is toggled to cool the unit runs all the time. The outside a/c contacts are engaged the entire time as well. The outside contacts will not disengage until I switch the Heat/cool switch back to heat and then the system shuts off and contacts on A/C disengage and all appears fine. Everything works just fine with the thermostat on heat. IE: the unit comes on and off like normal blows heat until set temp is obtained. Cold air blows just fine when heat/cool switch is selected to cool it just doesn't matter what the thermostat is set to the system just runs endlessly (woke up to a blissful 62 deg home first night it started )...I've completely disconnected the t-stat to see if that was it...the unit continued to run. I've gently given the relays and contacts,inside the control box, some extra persuasion, (rapped them with hammer a couple times,JK), to release if they were stuck...no luck there. Any Ideas or sugestions. Please and thank you in advance.

Regards,

[DaleM]

What type of thermostat is on the system? Is it a heat/cool thermostat or a heat only thermostat? The 2 wire sytem requires you to use a HEAY ONLY thermostat. The relays in the box are set up to recognize closed contacts on the ts-tat when in heat mode and open contacts on the t-stat when in cool mode. If someone put a heat/cool t-stat on the unit leave the heat/cool switch on the thermostat in the HEAT position and change between heat and cool on the realy box switches.

[mldman75]

Thanks that was it. I just bought this newly remodeled mobile home and it appears they replaced the t-stat. It does have the cool/heat switch. Would it be wise to order a new one or just operate it in the heat mode all the time? Also, as I was trying to figure out why the A/C was running all the time, I noticed a humming noise comming from the control box area. Is it a transformer and should I replace it? Thanks DaleM on the t-stat.

[DaleM]

Transformers hum, nothing to worry about. No need to change the thermostat as long as you understand the operation of it.