carrier

[frederick414]

anyone ever here of a unit doing this, 10 ton unit, ac and gas heat, when ever the fan contactor goes to pull in , it blows a 5 amp fuse on the main board. i took the low voltage terminal boaerd out of the cicuit and just jumpered the fan, instant blowing of the fuse. any help appreciated.

[tucsonbill]

I had one do just exactly that once. I found one of the wires running to the economizer was rubbing on some metal and would short the 5 amp 24v control fuse. (I am guessing thats the fuse you are referring to) One of the techs was tearing his hair out trying to find the cause.

You just have to get your meter out and start doing some detective work. Hope this helps.

[dmp3_16hvac/r]

I have had some units due that, i found that the contact was drawing excessive amps,, in my case the fuse was 3 amps and it draw 3.7 causing it to trip.

[hands]

I had the same problem on a carrier RTU one time. I thought it was the blower contactor coil, which will cause the same problem. But this time I found a bare spot in the thermostat wire. When the blower would start, the vibration and air flow would ground the wire and blow the fuse. If I keep the blower section access panel off, it wouldn't short out but as soon as I put the panel back it would blow the fuse. Check the blower compartment, I bet the t-stat wire is run through it and is rubbing on the fan housing. Try disconnecting the t-stat wires from the terminal board and place jumpers across the terminals to start the unit, if it still blows the fuse(or an inline circuit breaker for testing), then check the contactor.

[supertek65]

why not check Y to ground first, then ohm out contactor, I see alot of Carrier small rtu like 48tjf090 etc where the low voltage wires and pressure switch wires are rubbing on the suction line and blow fuses. on trane voyagers I have seen j-6 & j-8 blow on the ucp due to bad contactor coil. good luck. Frank

[frederick414]

i already took the stat wires off the low voltage terminal board, i also changed out the contactor, still blowing fuse!

[tucsonbill]

Frederick, you are just going to trace out the circuit with the help of the drawing, and find out where the short to ground is. Look at the drawing and see what all is energized when the blower contactor coil is energized. Even if it doesn't have an economizer installed, the wiring will be run to its location.

Sometimes you can see a spot rubbed on a wire, but like I said before, break out the meter and do a little detective work.

[frederick414]

to add to my problems, no drawing to follow, it got wet apparently and ruined, but i appreciate all the advice,i will find the problem and post it!

[jrbenny]

If you provide a complete model number, I will get a wiring diagram for you.

[frederick414]

found the problem today, the economizer was shorting out the circuit, it was on the 24 v side to the actuator! hey thanks for all the input.

[just_opinion]

Is it best?

To ask before to do

or

To do before to ask

when you are to be paid to do

[frederick414]

i did do before i ask!