Outside Unit Not Coming On

by Bob
(NJ)

I have a Carrier central air unit (model 38ed048300)manufactured in 1983. It has been serviced several times over the years. When I set the thermostat switch inside my home to "cool" the furnace blower comes on and everything appears to be ok at the furnace.


The fan on the external unit does not come on at all. I checked the two cartridge fuses (50A) in the fuse box near the AC, and they checked good with an ohmeter. When I had the fuse block out, I checked the voltage at the fuse box and there was about 25v AC across each of the fuse terminals. This voltage was there even with the thermostat switch inside the house set to "Off".

I also checked the main circuit breaker box in my garage to see if any breakers were tripped but none were. I even turned each circuit breaker off and then back on. It made no difference.

When I look inside (through the vent holes) my AC unit, everything appears to look relatively new. Should I take the cover off the AC unit and look more closely inside ? Is there anything else I can check ?

I appreciate any help you can provide.

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help NEW
by: Anonymous

Not getting any current to the condenser switch, would that be the thermostat or the control board on the air handler

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need help NEW
by: Anonymous

I've changed contactor and capacitor to outside unit but it still won't come on until I push in the button on d contactor. Inside circuit board with built in relays was replaced (because inside fan would not turn off) and it did go off but outside condenser is still dead.

what am I missing?

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need help NEW
by: Anonymous

I've changed contactor and capacitor to outside unit but it still won't come on until I push in the button on d contactor. Inside circuit board with built in relays was replaced (because inside fan would not turn off) and it did go off but outside condenser is still dead.

what am I missing?

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common fix NEW
by: Anonymous

The low voltage wires should be hooked up to common and yellow on your furnace to outside unit doesnt matter the orser you connect them its just making a switch that turns outside unit on or off if furnace is calling fot cooling the majority of the time the wires will arch due to bad crimps and loose fittings chexk your wiring make sure no arching happened to burn anything if it did clean it up and hook it back together and try again if it still doesnt work check capacitor likely it went bad and everything else is still ok start with simple stuff first

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My experience NEW
by: Anonymous

My outside a/c unit wouldn't come on but my heater fan did when I turned it into the fan on position and when my thermostat was in the cool position and fan on auto. Either way outside unit wouldn't come on.. I tripped my breakers still nothing so with knowing that electricity is supplying the unit I used a rubber handled straight screw driver and pushed in the contactor spring and the fan and compressor kicked on as long as I held the spring contactor in but when released it goes off. I learned that this could be due to low Freon but I had had my Freon charged just weeks before and knew I was good there and unit when working was blowing cold.. so I decided being that if you buy from a a/c supply place you can buy the capacitor and contactor cheap and replace them as I did. Problem fixed...I don't suggest anyone do what I did if they don't know what their doing. I know to turn the power off to the whole house and make a graph of the wiring to the parts to identify where they plug back into and make certain I get the same parts so that I don't have a problem identifying where the wires plug or screw in.. since I also updated my old thermostat with one just like I had. I turned the power to the house off checked to make sure the wiring connections was the same read the directions changed it and done.

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Condensation Pump NEW
by: Anonymous

Check your Condensation Pump first, that was my problem.

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Contactor
by: Anonymous

I have 240 volts on one side of the contactor in my AC condenser and 0 voltage on the other, does this mean the contactor is bad?

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Book
by: Anonymous

I have that book, what should I look for?

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Great Book
by: Dadan

this is NOT DIY site, and I really don't want a lawyer knocking on my front door.

if you're not familiar with electricity, it is not something to play with.

If you have a lot of time in your hand, there is a great book by Carrier, "hvac servicing procedures." You may find it useful.

Thanks for understanding

Dadan

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FAN
by: Anonymous

IS THERE ANY WAY TO BYPASS THE FAN TO IF IF THE COMPRESSOR WOULD KICK ON?

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5-TON AC CONDENSER UNIT
by: Anonymous

I HAVE A CARRIER 5 TON UNIT LIKE YOURS WITH THE SAME PROBLEM, HAS ANYONE COME ACROSS ANY SERVICE OR REPAIR MANUALS FOR THESE UNITS, I HAVE BEEN LOOKING, AND SINCE THEY ARE FAIRLY OLD I HAVE NOT HAD ANY LUCK YET. I HAVE BEEN ON OTHER SITES AND THINGS LIKE BAD STARTING OR RUN CAPACITOR, BAD STARTING RELAY, BURNED OUT COMPRESSOR MOTOR, BURNED OUT FAN MOTOR OR SEIZED BEARINGS ON THE FAN MOTOR, SOLENOID VALVE CLOSED, AN OPEN SWITCH, BURNED OUT CONTACTOR CONTACTS OR COIL, THE COMPRESSOR OVERLOAD OPEN OR SWITCH OPEN, ALL THESE HAVE BEEN MENTIONED AS POSSIBLE PROBLEMS. ALSO POSSIBLY LOW ON FREON, BUT IT SEEMS THESE OTHER PROBLEMS SHOULD BE ELIMINATED FIRST. DOES ANYONE KNOW HOW TO TEST FOR THESE? I HAVE DONE NOTHING TO MY CONDENSER UP TO THIS POINT, OTHER THAN CLEANING, OILING FAN MOTOR AND I HAVE CHANGED A TRANSFORMER ABOUT TWO YEARS AGO AND THE INDUCER FAN, ABOUT 15 YEARS AGO ON MY NATURAL GAS FURNACE ALONG WITH THE GENERAL MAINTENANCE FOR THE FURNACE. I WOULD LIKE TO FIX THEM RATHER THAN REPLACE THEM RIGHT NOW. THEY HAVE BEEN VERY RELIABLE UP TO THIS TIME.

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Fan or Capacitor
by: Anonymous

I have same unit. Either your fan motor is dead or you have a bad capacitor. The compressor won't operate unless the fan works.

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Where the unit wire diagram?
by: Anonymous

It would save a lot of thinking and educational guesses, if someone would provide a wire diagram of the unit.


Sincerely,

Need Pix

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not coming on
by: mtsflorida

Do you have a 24v electrical relay, is the thermostat getting voltage, do you have a voltmeter, does the main breaker send voltage, how about the breaker near the blower, or lastly the breaker near the big condenser fan outside?
From the drip pan runs a white pvc pipe that contain a sensor, that sometimes has water stuck inside that is preventing the system from getting power. Water must be able to drain from the drip pan or it will not work. Wires could be loose going to the thermostat from the relay. You can try to bypass the relay and send 24v straight to the themostat along the red lead or lead labeled for what is desired (i.e. heat, cold, high, low pressure) but that could cause a short, so don't even consider it.

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Same problem here
by: Anonymous

Did any one find the solution yet? Please let us know.

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condensate removal pump?
by: Anonymous

Could it be your condensate removal pump? When the pump breaks the condensate (Water) reservoir fills up. When it is full the outside unit will not come on and you will continue cycling your inside air through the blower. Some brands use other forms of condensate removal. This is one problem to consider.

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Re:Outside Unit Not Coming On
by: Chad

I am having the same problem. I have a Trane AC unit which is a 3or so yrs old..so basically still brand new. I just took the cover off and flipped the breaker inside the house to on. The furnace Blower goes on and stays on, but the outside unit (Fan and compressor) have not. I check all connections, and all is fine. I verified that power is coming to the outside Unit. The outside Box is fine. I even checked the wires going to the Thermostat (Honeywell) and all is fine. Same about the wires going to the Furnace.
I have Yellow, Green, White and Red between the Furnace and the Thermostat. and I have Red and White from the AC unit to the Furnace. the white from the AC Unit connected the white in the Furnace, the Red from the AC unit is connected to a slot that has the letter "C" on it, beside the "R" where the red from the Thermostat connects to.

I am hoping these wires are connected correctly.
I even opened the cover on the AC unit and check all connections, and all were fine, noting loose and all are getting power..

I never had any problems before and always turn the breaker inside off for the AC unit winter season and cover the unit.

Could this be a refrigerant problem?
is it a Thermostat issue, not sending a signal?
are the wires from the Thermostat to the Furnace and from the AC unit to the Furnace connected properly?
Do I have a bad fuse somewhere, where could it be?

Any help would be greatly appreciated

Thanks!

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