heat blower comes on intermittently

[roy]

Hope someone can help me with this. I have an electric central ac/heat unit on my roof. When it gets cold out (in arizona) I turn the heat on and what happens as its been happening this morning is that I can hear some fan come on am thinking its the exhuast fan but no heat comes out of the vents. Now this morning I tried it about eight times turning it off and on to see if it would kick in and my wife just tried it as I'm typing this and it starts working. You can hear like a woofing sound and the heat starts coming out. This has been happening for the last week and we don't want to take the chance of leaving the setting on auto because it comes on (the heat blower am thinking) when it wants to. Please help. Thanks
PS. It also does the same thing if I turn on the cold air.

[Wgoodrich]

Is this an electric furnace only or an air to air heat pump with electric furnace assist? If this is a heat pump the heat pump will produce heat mainaining the heat temp in your house up to about 30 degrees outside when the electric heat assist will have to help maintain the heat output to maintain inside temp. If a heat pump in auto mode the air coming out of the blower will only be a few degrees warmer [almost not noticable] than room temp. Only when the assist heat comes on will you feel heat coming out of the heat ducts. Otherwise when heat pump is doing the heating the temp maintains in the house with a constant fan blower motor running and low temp rise coming out of the heat ducts.

The thermostat of a heat pump system has two bubbles in it. They are about 2 degrees off each other. This way in auto mode the heat pump maintains until the second bubble calls for heat then that second bubble will auto turn on your assist heat. Don't worry let it run on auto if heat pump system with assist furnace.

Trick to heat pump systems. Remember the 2 degree bit in the thermo. If the temp outside is hanging at 30 degrees or more turn your thermostat up 3 degrees. This will cause the heat pump to maintain inside temp what your body is used to. Otherwise whenever assist heat is not needed the temp in your house will drop that two degree difference between the two bubbles in the thermostat. Your body will feel these two degree change. This is why you hear many complain they are always cold due to heat pump system. Turn up termostat 3 degrees if outside temp is 30 degrees or above. Turn down 3 degrees on thermostat if outside temp is below 30 degrees.

When heat pump is running the blower on the furnace will run almost constant with little or no feel of heat coming out of the ducts but the heat pump is maintaining the heat in your home. Just something you have to get used to. I have a heat pump system air to air and it has done me fine with comfort for 25 years economically. Just remember that 30 deree outside air thermostat 3 degree adjustment. You will like you heat much better.

If all else fails such as problems with the heat pump the assist heat will kick in when on auto with only the 2 degree drop in home ambient temperature.

Hope this helps

Wg

[mdshunk]

WG... is it possible that this gentleman's RTU is gas-fired? The "blower noise" with no heat could be prepruge and then no proof of ignition. When he tried it eight times, got a big woof, and then heat, could that have been the woof of a not-too-swift gas ignition? I know he said the unit was electric and that would mean heat pump, but I'm just thinking outside of the box here.

He did say AZ? Must be heat pump in retrostpect. Ramble, ramble, ramble.

[roy]

What I have a is an electric central Trane Weathertron heat pump. Like i said it comes on if i keep turning it off on for a while in auto. Also, if I just turn it to the on fan setting all I hear is a humming sound and the fan doesn't come on.
I notice that it happens only when its really cold out. I know that the pump works after a few trys so am wondering if there is some part that is failing that i need to get.

[mdshunk]

If I understand the problem... 1) If you put the FAN-OFF-AUTO switch to fan, you hear humming and the fan does not come on and 2) If you put it on AUTO and set the thermostat to a call for heat, the blower only works intermittantly.

I have a couple-o-ideas. The humming could be a bad fan contactor. I've seen these fail and sould like an electric razor just sitting there humming. Could also be low voltage on the 24 volt circuit from a variety of things (bad contacts in a safety, bad contacts in the 'stat, bad transformer, etc.) Could also be a weak capacitor on the blower motor if the motor is equipped with a cap. Could the blower motor bearings just be in need of oiling?

Trane is part of my line, so with model and serial I could help you sommore. Someone else might have another light bulb go on with the info you've provided so far. I know that if I was at your house I could have it pinned down in about 2 minutes. It's hard to troubleshoot on a message board.

[Wgoodrich]

I am a bit concerned that you may be playing with this system to much. Please be aware a compresser builds up pressure. When this compressor is turned off it should stay off for about 5 minutes to relieve that pressure from the compressor head in order for it to restart. If you are turning it on and off in succession then you are asking to destroy your heat pump. If you turn it off. Leave it off for about 5 minutes before you retry. There are overloads that will try to protect your system but if you do this cycling too often these safety measures will fail you and cause damage to the system.

May be a capacitor or other component. May be you are not used to the system. Just be aware you can damage this system by playing with it on and off too much.

Are you saying the heat pump won't come on or the fan won't come on or that the fan will come on but the air coming from teh ducts are not warm?

Be careful

Wg

[mdshunk]

Could be so many things... just more info needed like exactly what is running, what is not running, and where the noises are. The humming could be the condenser fan running on a call for heat and the compressor is hard to start because of age, low voltage or whatever. If this were the case, a hard-start kit would solve the problem. I concur that you should not "short-cycle" this system too much. Many of the Trane models have anti-short cycle timers that prevent you from doing any real damage, but I wouldn't bet money that your particular model has an anti-short-cycle timer.

[roy]

I got it to work. It seem like the problem was a faulty thermostat. I pulled the old one out and replaced it with a new one and the heat blower came on right away. I would like to thank you Wgoodrich and mdshunk for all help.
This is a great site and I will recomment it to all my friends. Thanks again.
Roy.

[mdshunk]

I'm glad that you found your problem. When I begin an HVAC troubleshooting call, and I have an idea that it could be one of several things, I generally start checking the things first that "people touch". Things that prople touch are often worn from heavy use, abuse, misadjusted or otherwise rigged. You saved yourself a couple of hundred bucks. Bravo.