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Discussion Starter · #1 ·
Have a Lennox HP-036-7P. It cools great for about 10 minutes and then the compressor stops. When this happens everything else keeps running but the compressor. The LED's on the board are both flashing which per the manual means everything is ok. The condenser and evaporator coils are clean and the filter is new.

3 years ago the dual capacitor was replaced by a HVAC tech with two individual capacitors because he did not have a dual one. The unit has worked fine since then. While the compressor is running the cap for it read 330 volts, when it stops it reads 120 volts.

What should I look at a to fix the issue? Is the a DIY thing or do I need a HVAC tech to make the repairs?

Thanks,
Sean
 

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By compressor, do you mean the entire condensing unit or the compressor itself?

If it's the compressor, does it restart again after a few minutes? It could be the thermal overload cycling due to excess amp draw or another issue. Have you checked the amp draw with a clamp meter?

Are you looking at leds on the defrost board in the condenser or the control board in the air handler/furnace?
 

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Discussion Starter · #3 ·
The compressor itself is the part shuting down, the fan on the condenser keeps running.

The LED's are on the board in the condenser.

I have not measure the amps. I just tried and the compressor will not run. The compressor is very hot to the touch. I have the panel off and when it cools I'll get the amp draw.

When the compressor stops I assume it starts on its own again but I have not seen that happen. I've been turning the system off and then turning it back on again in a few hours.

Thanks for your reply.
 

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Run the unit and soon as it shuts down, pull the disconnect, disconnect the wires leading to the compressor and ohm out the windings.

With the overload open you should get a resistance between terminals R and S, but not R-C or S-C until the overload closes again.

If the overload is opening the following should be checked:
1. Run capacitor
2. Amp draw
3. Operating pressures and temperatures -> low charge, restriction, check valve issue, or failed txv. (call a tech for this)

Don't keep on running it as it because the compressor can get damaged. You have a nice quiet machine (the new ones have the compressor under the fan), high efficiency in its day which is definitely worth fixing even if the indoor coil is leaking.

The 3rd and 4th digits of the serial number indicate the manufacturing date.
 

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Discussion Starter · #6 ·
By compressor, do you mean the entire condensing unit or the compressor itself?

If it's the compressor, does it restart again after a few minutes? It could be the thermal overload cycling due to excess amp draw or another issue. Have you checked the amp draw with a clamp meter?

Are you looking at leds on the defrost board in the condenser or the control board in the air handler/furnace?
Just checked the amps.
Starting 11.3 amps on each leg
Running 10.5a on one leg 9.9a on the other leg, the wire from the cap was 9.9a too.
When the compressor stopped the amps on the 10.5a leg stayed there it did not spike.

What does this indicate? Low charge?
 

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Discussion Starter · #7 ·
Run the unit and soon as it shuts down, pull the disconnect, disconnect the wires leading to the compressor and ohm out the windings.

With the overload open you should get a resistance between terminals R and S, but not R-C or S-C until the overload closes again.

If the overload is opening the following should be checked:
1. Run capacitor
2. Amp draw
3. Operating pressures and temperatures -> low charge, restriction, check valve issue, or failed txv. (call a tech for this)

Don't keep on running it as it because the compressor can get damaged. You have a nice quiet machine (the new ones have the compressor under the fan), high efficiency in its day which is definitely worth fixing even if the indoor coil is leaking.

The 3rd and 4th digits of the serial number indicate the manufacturing date.
The overload tests open
The amp draw is ~10.5a
The capacitor test good by ohms (I do not have a way to check it another way)
I do not have a way to check pressures, guess I'll call service

Thanks very much for your assistance.
 

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Doesn't sound out of line, but what's the amperage on the common side? That's a more definitive measurement than doing run and start due to power factor/phase shift and other motor characteristics. I don't know what the current should be on R and S.

What's the RLA on the nameplate?

HP26 is a 13 seer -> wouldn't expect very high amps, maybe 10-11 in very hot weather.
 

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Rule out the capacitor first.

Symptoms of low charge are a low temperature difference across the air handler, sound of gas bubbles moving through liquid line, or a warmer than normal suction (insulated line) A warmer suction line (maybe above 60-65F, normal would be 45-60 in typical conditions) would be needed to cause the compressor to overheat and cycle on overload unless there's an issue not related to charge.
 

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Just checked the amps.
Starting 11.3 amps on each leg
Running 10.5a on one leg 9.9a on the other leg, the wire from the cap was 9.9a too.
When the compressor stopped the amps on the 10.5a leg stayed there it did not spike.

What does this indicate? Low charge?
The overload tests open
The amp draw is ~10.5a
The capacitor test good by ohms (I do not have a way to check it another way)
I do not have a way to check pressures, guess I'll call service

Thanks very much for your assistance.
A couple of things are not adding up and it may be in your favor if your measurements are correct. If the internal thermal switch is opening the 10.5 amps should go to zero. You do have a way to measure the capacitor. Amps X 2650 / voltage. Assuming that you have 240 volts, you can double check that voltage, I'm seeing 109mf which seems too large.

So you may have a partially shorted run capacitor that is causing your problems.
 

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Discussion Starter · #12 ·
Have a Lennox HP-036-7P. It cools great for about 10 minutes and then the compressor stops. When this happens everything else keeps running but the compressor. The LED's on the board are both flashing which per the manual means everything is ok. The condenser and evaporator coils are clean and the filter is new.

3 years ago the dual capacitor was replaced by a HVAC tech with two individual capacitors because he did not have a dual one. The unit has worked fine since then. While the compressor is running the cap for it read 330 volts, when it stops it reads 120 volts.

What should I look at a to fix the issue? Is the a DIY thing or do I need a HVAC tech to make the repairs?

Thanks,
Sean

A service tech came out today. Below a the issue with this a/c:
- low charge, small leak in the condenser and evaporator coil - both will be replaced
- bad/stuck expansion valve at the evaporator

Glad the warenty is still good as an expensive repair was cheep. Thanks for all the advice above.
 
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