# high pressure switch tripping



## rortiz38 (Mar 15, 2013)

I have a 3.5 ton 22 year old lennox compressor that I am trying to make it through the rest of the summer with. Two days ago the high pressure switch kicked the unit off. I reset it and it ran for the rest of the day. Yesterday it kicked off again in the afternoon. I reset it several more times(it is 97° in Houston today). Each time it would run for a short period of time then kick off again. After 3 resets, I pushed the button and it hummed but the fan would not spin. 20 seconds and it tripped. I removed the fan guard, reset it and manually gave it a spin, not with my hand, and it slowly kicked on. A few minutes later it was dead again. After extensively searching forums and testing everything I could with my millimetre, I went to Johnstone and picked up two new capacitors and a new fan motor. Capacitors went on first, it ran for a while, I left then got the call it was hot again. I came back and hooked up the new motor and it tripped the h.p. switch with in a minute. Next I cut out every questionable terminal connector and replaced them but I'm still getting the same result. When I reset the switch, it will run for 20 seconds to a minute or two, the fan will cut out and I will continue to hear the compressor hum for about 10 seconds before popping the switch. I have not tested the contactor or start relay yet. 
Can anyone smarter than me(probably everyone hanging out in this forum) give me any direction on where to go next? I'm preparing for the bad news.
Thanks
Ricky


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## flashheatingand (May 3, 2008)

Too lengthy to walk through what to check. Here are a couple of quick things to check: Rotation of the fan, make sure it's spinning in the right direction. Wash the outdoor coil. A lot of those older coils have a layer of dirt between the two coils (kinda lie the filling on an Oreo cookie). More times than not, it's a dirty coil, or a bad fan motor. If you just replaced the fan motor, at least make sure it's spinning in the right direction.


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## rortiz38 (Mar 15, 2013)

flashheatingand said:


> Too lengthy to walk through what to check. Here are a couple of quick things to check: Rotation of the fan, make sure it's spinning in the right direction. Wash the outdoor coil. A lot of those older coils have a layer of dirt between the two coils (kinda lie the filling on an Oreo cookie). More times than not, it's a dirty coil, or a bad fan motor. If you just replaced the fan motor, at least make sure it's spinning in the right direction.


Thanks for the advice. The fan direction checks out. I actually washed the coil down with the hose the first time it tripped. I went out and washed it thoroughly again tonight. The fins are beat up pretty bad but there has not been any change from when it worked one day to the next when it will not run for more than a minute. 
I am going to try putting my meter on the relay and then the contactor and switching it on to see if I can tell where the power of cutting off. 
-Is it possible there could be a clogged line that is causing pressure to build when the compressor kicks on?
-could this be a failing compressor and if so, would it cause a fan to kick off before the compressor?
seems to me that it would be something electrical cutting out that kills the fan and overheats the compressor but I'm not an hvac guy. 
Thanks.


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## beenthere (Mar 5, 2009)

Sounds like it may be that they gave you an incorrect condenser fan motor.

Does it match the old motor? RPM, voltage, and amp draw.


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## rortiz38 (Mar 15, 2013)

beenthere said:


> Sounds like it may be that they gave you an incorrect condenser fan motor.
> 
> Does it match the old motor? RPM, voltage, and amp draw.


The numbers are all the same. The new motor was slightly taller and I had to trim a few inches off the spindle to fit the grill back on but it fit.


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## WyrTwister (Jul 19, 2013)

rortiz38 said:


> Thanks for the advice. The fan direction checks out. I actually washed the coil down with the hose the first time it tripped. I went out and washed it thoroughly again tonight. The fins are beat up pretty bad but there has not been any change from when it worked one day to the next when it will not run for more than a minute.
> I am going to try putting my meter on the relay and then the contactor and switching it on to see if I can tell where the power of cutting off.
> -Is it possible there could be a clogged line that is causing pressure to build when the compressor kicks on?
> -could this be a failing compressor and if so, would it cause a fan to kick off before the compressor?
> ...


 

I am puzzled ? Contactor I understand . But what relay are you refering to ?


As long as you are not tripping the circuit breaker or blowing fuses , I can not think of anything , on an older unit , that would tie / connect / link refrigeration problems with condensor fan problems ( electrically ) . Except the contactor .

If in doubt , go back to Johnstone & get a new contactor . They are not that $$$ and I think you said the unit was 22 years old ? It may not be quite shot , yet , but I will confidently bet it has seen its better days ? A new one would be inexpensive " insurance " .

Did you say the fins on the condensor coil are messed up . Are they salvagable enough that fin comb would help ? ( You still have to get the condensor fan issur solved . ) 

Is the motor a multi voltage & it is on the wrong voltage ?

You sure you have the correct capacitors and they are connected correctly ?

The fan motor only have a single speed ? You said the rotation and the air flow is correct ?

Worst case , can you wire the fan motor direct ( for a test ) to power & its capacitor , to make sure nothing else is causing your problem ?

Did you end up with 2 individual / seperate capacitors of one larger capacitor that is really 2 in one case ( those have 3 terminals , I think ) ?

God bless
Wyr


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## flashheatingand (May 3, 2008)

Old Lennox A/C? Is the fan mounted underneath the coil? If so, you need to make sure the underside of the coil is clear? Generally speaking, refrigerant issues don't arise on a 22 year old system. If so....


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## flashheatingand (May 3, 2008)

rortiz38 said:


> I have a 3.5 ton 22 year old lennox compressor that I am trying to make it through the rest of the summer with. Two days ago the high pressure switch kicked the unit off. I reset it and it ran for the rest of the day. Yesterday it kicked off again in the afternoon. I reset it several more times(it is 97° in Houston today). Each time it would run for a short period of time then kick off again. After 3 resets, I pushed the button and it hummed but the fan would not spin. 20 seconds and it tripped. I removed the fan guard, reset it and manually gave it a spin, not with my hand, and it slowly kicked on. A few minutes later it was dead again. After extensively searching forums and testing everything I could with my millimetre, I went to Johnstone and picked up two new capacitors and a new fan motor. Capacitors went on first, it ran for a while, I left then got the call it was hot again. I came back and hooked up the new motor and it tripped the h.p. switch with in a minute. Next I cut out every questionable terminal connector and replaced them but I'm still getting the same result. *When I reset the switch, it will run for 20 seconds to a minute or two, the fan will cut out and I will continue to hear the compressor hum for about 10 seconds before popping the switch.* I have not tested the contactor or start relay yet.
> Can anyone smarter than me(probably everyone hanging out in this forum) give me any direction on where to go next? I'm preparing for the bad news.
> Thanks
> Ricky


Fan and compressor are controlled by the relay. Perhaps you wired the fan motor incorrectly?


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## WyrTwister (Jul 19, 2013)

The crankcase heater should be on the line side of the contactor ( relay ? ) .

Fan and compressor on the load side ( each having a run capacitor , of different values ) .

The only relay I can think of would be for a hard start kit , on the compressor ( along with a start capacitor ) ?

God bless
Wyr


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## beenthere (Mar 5, 2009)

So the fan blade is not up as high as it use to be with the OEM motor?

When the motor does run, what is its amp draw.


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## Jeremy Bednarsh (Aug 16, 2013)

What's the condition of the condenser coil ? Is it clean? What are your pressures and temps? What's The superheat and sub cooling ? How do you have the fan wired? You always want to replace fan with at least the same amperage.


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