Trane heat pump with a bad sump heater

Posted by The Daring Dufas on July 11, 2009, 10:10 pm

Jerry wrote:

> I have a Trane XL1400 3 ton heatpump. The breaker for the outdoor unit
> instantly trips and this is with the air conditioning thermostat set to off,
> so my problem lies on the line side of the contactor, L1 and L2. I have the
> wiring schematics for my unit and I discovered that if I detach the wire
> going from either L1 or L2 to the sump heater that the breaker will no
> longer trip. What I need to know is if the sump heater is something that is
> separate from the compressor and can be replaced without disturbing the it.
> I'm fairly knowledgeable about electronics and electrical wiring but know
> absolutely nothing about the freon side of an air conditioner.
> Thanks.
>
>

I think what you're referring to is the crankcase heater.
The heater is on whenever there is power on the condensing
unit. There are two types you will see on HVAC compressors.
One looks like a long screw type hose clamp that wraps around
the lower part of the compressor and the other is a ceramic
cartridge that slips into a well in the side of the lower
crankcase of the compressor. The ceramic heater will be coated
with a heat transfer compound that resembles white grease
and held in place with an internal spring clip. If either type
heater is shorted somehow, it will trip the circuit breaker.
The heaters are easily replaced without disturbing the hermetic
system. There are some heater systems that apply a limited
current to the motor windings to keep the compressor warm but
I haven't seen it on a home HVAC system.

TDD

Posted by Steve on July 12, 2009, 11:47 am

There are some heater systems that apply a limited

> current to the motor windings to keep the compressor warm but
> I haven't seen it on a home HVAC system.

This is common practice by the manufacturers in resi systems.

Posted by The Daring Dufas on July 12, 2009, 12:06 pm

Steve wrote:

> There are some heater systems that apply a limited

>> current to the motor windings to keep the compressor warm but
>> I haven't seen it on a home HVAC system.

>
> This is common practice by the manufacturers in resi systems.
>
>

Educate me, what brands? I'd like to know so
I don't break one. Some years ago, a friend
asked me to check out a system he had just
installed because he thought something was wrong
with it. I thought something was wrong too
until I read the documentation and spoke with
the distributer. I had no experience with the
electronically controlled blower motors at the
time and had to be educated. I started repairing
AC units back in the early 1970's and have seen
a lot of changes since then. The modern equipment
is like a new toy for me when I discover how they
work.

TDD

Posted by Steve on July 12, 2009, 10:48 pm

> Steve wrote:

>> There are some heater systems that apply a limited

>>> current to the motor windings to keep the compressor warm but
>>> I haven't seen it on a home HVAC system.

>> This is common practice by the manufacturers in resi systems.

> Educate me, what brands? I'd like to know so
> I don't break one. Some years ago, a friend
> asked me to check out a system he had just
> installed because he thought something was wrong
> with it. I thought something was wrong too
> until I read the documentation and spoke with
> the distributer. I had no experience with the
> electronically controlled blower motors at the
> time and had to be educated. I started repairing
> AC units back in the early 1970's and have seen
> a lot of changes since then. The modern equipment
> is like a new toy for me when I discover how they
> work.
> TDD

Rheem/RUUD, most Carrier/Bryant/Payne, as well as most ICP products. when
you open one up that still has the *ORIGINAL* contactor, you will probaly
find that it has a single pole contactor with a shunt. FWIW, *MOST* scroll
compressors use the start windings for CCH.

Posted by The Daring Dufas on July 12, 2009, 11:07 pm

Steve wrote:

>> Steve wrote:

>>> There are some heater systems that apply a limited
>>>> current to the motor windings to keep the compressor warm but
>>>> I haven't seen it on a home HVAC system.
>>> This is common practice by the manufacturers in resi systems.

>> Educate me, what brands? I'd like to know so
>> I don't break one. Some years ago, a friend
>> asked me to check out a system he had just
>> installed because he thought something was wrong
>> with it. I thought something was wrong too
>> until I read the documentation and spoke with
>> the distributer. I had no experience with the
>> electronically controlled blower motors at the
>> time and had to be educated. I started repairing
>> AC units back in the early 1970's and have seen
>> a lot of changes since then. The modern equipment
>> is like a new toy for me when I discover how they
>> work.
>> TDD

>
> Rheem/RUUD, most Carrier/Bryant/Payne, as well as most ICP products. when
> you open one up that still has the *ORIGINAL* contactor, you will probaly
> find that it has a single pole contactor with a shunt. FWIW, *MOST* scroll
> compressors use the start windings for CCH.
>
>

Thanks, I hadn't really noticed it on the wiring diagrams.
In truth, I haven't had to replace that many scroll
compressors. Tomorrow I have to help a friend, who I do
a lot of HVAC work with, change out a 1.5 ton recip. I
will look for the circuit now and be careful to make sure
the crankcase heat is on for any of the scroll compressors
I come across. And I thought the manufacturers were just
being cheap with that single contact.

TDD

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Trane heat pump with a bad sump heater - Page 3