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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8670
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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installed brand new copressor just humms...

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installed brand new copressor just humms... new cap as well....getting 240 trying to recharge. but comp. wont start.?

i am epa certified type 2

Welcome to Just Answer!.

There are 3 wire connections at the compressor... marked, C, S and R.

I need the amperage readings from a clamp around type amp meter on each of those wires when the compressor is not starting, just humming.

We can go from there until we get this resolved..

Customer: replied 4 years ago.

i dont have an amp draw meter with me ....


Hello again, we will need amperage readings in order to diagnose the problem.

Most likely it is not wired correctly at the run capacitor. If there is no black plastic round capacitor, called a start capacitor, and just the metal tin can shaped 'run capacitor' it is wired this way

From the contactor Line 1 should go to Common on the compressor (C),
Line 2 should go to both Run on the compressor (R) ..*and to one side of the run capacitor... the other side of the run capacitor should go to S on the compressor.

If there is a round black plastic capacitor it is more complex... we can discuss that next if necessary,

Check that and let me know, I am off to bed in half an hour, if I miss you tonight I will be back on line in the morning west coast of the US time.

Customer: replied 4 years ago.

i located a amp draw meter will test now but yeah i have s to herm on cap and the other lines on either side of the contactor



I will wait up for your results

Customer: replied 4 years ago.

s is 4.7 left leg is 4.7 right leg is 0

Good work!

However I need to know which is C, S and R... 'right and left' doesn't tell me anything.

C,S and R should be stamped into the metal or fiber support at the compressor terminals

The fact that one leg is zero indicates its wired wrong most likely.

Customer: replied 4 years ago.

c is 0 r is 4.7 s to cap is 4.7 its a single pull single throw contactor c is on the throw side

Hello again,

You have it wired incorrectly but I can't tell what the error is from here without some testing.

We know that you have both Line 1 and Line 2 attached to the compressor or you would not be getting 4.7 amps between S and R.

Look closely at where C attach's at the contactor... and then check the voltage between C and R

We can go from there
Customer: replied 4 years ago.

im getting 240 across both c and r i have c connected to the pull throw side and the jumper from the contactor to cap is on the same side as c... i looked for a saftey switch but didnt see one ...i did have a problem with the saftey switch on the air handler which prevented the contactor from pulling but bypassed that and the contactor is pulling like it should....should i try reversing c & r ?


one side of the cap should go to S on the compressor.
The other side of the cap should go to R...not C

C should be Line 1, R should be Line 2

We keep going until we get it working as long as you rate my answers *positively I hold the question open

Customer: replied 4 years ago.

cool compressor is running but its not sucking in freon....i have the blue to low side yellow to tank... bottle is open manifold knob open just reading 10 psi. compressor off its reading around 50 psi... is the compressor running in reverse ?

Hello again, good work on the wiring,

Compressor will not run in reverse. You have the gages and valves hooked up and not opened properly.

I can coach you on that if you rate my work so far *positively,

Phil and other HVAC Specialists are ready to help you
Customer: replied 4 years ago.

i charge units all the time . i dont understand although this is my first heat pump syatem i have worked on.. i always charge on the low side. plse help me understand


Thanks for the positive rating.

Tell me if you have evacuated the system using a vacuum pump, and then tell me what refrigerant it uses, and if it says to liquid charge or vapor charge the refrigerant.

To charge the system put the system in cooling mode... and put the blue gage hose on the suction service valve port. then back the valve out all of the way... then after it is backed out all the way, turn it one turn clockwise.

Hook the red gage hose to the liquid line service port and adjust that the same way.

Hook the center service manifold port to the charging cylinder.

Run the heat pump in cooling mode and slowly meter liquid refrigerant into the suction side, (blue hose).


compressor must be running at all times, if the compressor begins to frost at all you are feeding refrigerant in too fast. listen to the compressor, if starts to sound noisy or heavily labored, feed the refrigerant in more slowly


Tell me what refrigerant the system uses

Tell me how that goes.


Customer: replied 4 years ago.

thats what i did..? im wondering if the air handler is wired wrong from the t may be in heat mode when i put it on cool.. because it will take a charge when i put it in heat mode.?


Hello again, it is close to 2 am here, tell me where you are in the world so we can work this so I get some sleep

if its in heat mode when you put it in cool mode .... look on the thermostat for an O and a B terminal...move the wire from whichever O or B terminal its on, to the other terminal.

Tell me how that goes.

I still need to now what refrigerant you are using. I am off to bed shortly. If I miss you I will be back in about 8 hours.

Customer: replied 4 years ago.

r22... i dont use o or b....y wire goes to y and w.... w wire goes to on and so forth but blue goes to c.. get some sleep phil thx for ur help....


You are using the wrong kind of thermostat most likely. Unless it says for heat pumps on the box its wrong. Most heat pump thermostats have an O and a B terminal. that operates the reversing valve.

The type that have no O and B terminal and are for heat pumps are complex and programmable.

Charge the system until it operates in cooling mode, with the house at 72F and the suction pressure between 59 and 60 psig

Look that thermost issue over carefully.

I am off to bed, see you in the morning,

Customer: replied 4 years ago.

thx for ur help phil........