Hi everyone.

I have a central air conditioning unit in my ranch-style home (full
basement also). Yesterday the AC just kicked off randomly. I checked
the thermostat and it seemed to be functioning ok (it's digital). I
went downstairs to the power switch dedicated to the central air unit
and turned it off, then back on again. The AC kicked back on, stayed
on and started blowing cool air, then kicked back off again 2 minutes
later.

I suspected there was an airflow problem of some type (filter, etc)
but that doesn't appear to be case, at least not as far as I can
tell.

Are there any other common causes for this type of behavior?

Thank you for any responses,
Mike

Check the outside unit. Is the fan turning at normal speed? Anything blocking the airflow?

If the outside unit wasn't getting enough airflow, the high-pressure switch could cause it to cut out.

Also could be a problem with the compressor motor, start circuit, or capacitor, causing the thermal overload to trip.

Eric Law

"Mike" wrote in message ups.com...
Hi everyone.

I have a central air conditioning unit in my ranch-style home (full
basement also). Yesterday the AC just kicked off randomly. I checked
the thermostat and it seemed to be functioning ok (it's digital). I
went downstairs to the power switch dedicated to the central air unit
and turned it off, then back on again. The AC kicked back on, stayed
on and started blowing cool air, then kicked back off again 2 minutes
later.

I suspected there was an airflow problem of some type (filter, etc)
but that doesn't appear to be case, at least not as far as I can
tell.

Are there any other common causes for this type of behavior?

Thank you for any responses,
Mike

On Thu, 30 Aug 2007 19:22:10 -0000, Mike
wrote:

Hi everyone.

I have a central air conditioning unit in my ranch-style home (full
basement also). Yesterday the AC just kicked off randomly. I checked
the thermostat and it seemed to be functioning ok (it's digital). I
went downstairs to the power switch dedicated to the central air unit
and turned it off, then back on again. The AC kicked back on, stayed
on and started blowing cool air, then kicked back off again 2 minutes
later.

I suspected there was an airflow problem of some type (filter, etc)
but that doesn't appear to be case, at least not as far as I can
tell.

Are there any other common causes for this type of behavior?

Thank you for any responses,
Mike

The compressor may be drawing to much current and a bi-metallic
safety switch is shutting it down or the cooling fan for the coil is
not functioning and causing a over temp fault.

On Aug 30, 3:40 pm, wrote:
On Thu, 30 Aug 2007 19:22:10 -0000, Mike
wrote:



Hi everyone.

I have a central air conditioning unit in my ranch-style home (full
basement also). Yesterday the AC just kicked off randomly. I checked
the thermostat and it seemed to be functioning ok (it's digital). I
went downstairs to the power switch dedicated to the central air unit
and turned it off, then back on again. The AC kicked back on, stayed
on and started blowing cool air, then kicked back off again 2 minutes
later.

I suspected there was an airflow problem of some type (filter, etc)
but that doesn't appear to be case, at least not as far as I can
tell.

Are there any other common causes for this type of behavior?

Thank you for any responses,
Mike

The compressor may be drawing to much current and a bi-metallic
safety switch is shutting it down or the cooling fan for the coil is
not functioning and causing a over temp fault.

I'm not really an AC expert, so the items I see to check:
1) Fan on the compressor unit outside the house
2) Ensure nothing is blocking airflow in or around the outside unit
3) Compressor drawing too much current (any way to check this, I do
have a multimeter)

On Aug 30, 4:49 pm, Mike wrote:

snip

3) Compressor drawing too much current (any way to check this, I do
have a multimeter)

You need an AC ammeter or the right adapter to handle 50 A more or
less on your multimeter. HTH

Joe

Joe wrote:
On Aug 30, 4:49 pm, Mike wrote:

snip

3) Compressor drawing too much current (any way to check this, I do
have a multimeter)

You need an AC ammeter or the right adapter to handle 50 A more or
less on your multimeter. HTH

Quite an adapter to put inline w/ a conventional multimeter...

In a practical sense, unless you have a clampon meter, no, there isn't
an easy way for large currents...typical VOM's are able to handle only a
few 10's of mA.

--

"dpb" wrote:
Joe wrote:
On Aug 30, 4:49 pm, Mike wrote:

snip

3) Compressor drawing too much current (any way to check this, I do
have a multimeter)

You need an AC ammeter or the right adapter to handle 50 A more or
less on your multimeter. HTH

Quite an adapter to put inline w/ a conventional multimeter...

All you need is a length of wire (or a resistor) to use as a shunt, inserted
in parallel with the load.

In a practical sense, unless you have a clampon meter, no, there isn't an
easy way for large currents...typical VOM's are able to handle only a few
10's of mA.

My cheapy Harbor Freight DMM measures up to 20A AC current, but most common
meters usually only measure a few hundred mA of DC current.

Jon

Jon Danniken wrote:
"dpb" wrote:
Joe wrote:
On Aug 30, 4:49 pm, Mike wrote:

snip
3) Compressor drawing too much current (any way to check this, I do
have a multimeter)
You need an AC ammeter or the right adapter to handle 50 A more or
less on your multimeter. HTH
Quite an adapter to put inline w/ a conventional multimeter...

All you need is a length of wire (or a resistor) to use as a shunt, inserted
in parallel with the load.

Yeah, but...if needed to ask, that's not just a "just" w/ 50A...

--

Mike wrote:
Hi everyone.

I have a central air conditioning unit in my ranch-style home (full
basement also). Yesterday the AC just kicked off randomly. I checked
the thermostat and it seemed to be functioning ok (it's digital). I
went downstairs to the power switch dedicated to the central air unit
and turned it off, then back on again. The AC kicked back on, stayed
on and started blowing cool air, then kicked back off again 2 minutes
later.

I suspected there was an airflow problem of some type (filter, etc)
but that doesn't appear to be case, at least not as far as I can
tell.

Are there any other common causes for this type of behavior?

Thank you for any responses,
Mike

When you say that you turned off the power switch, are you talking about the
120-volt toggle switch?

If that is all you did, you had to have reset something and it could be a
number of things. Your thermostat, safety control or control board. Your
best bet is call out your HVAC company to have them check pout your system.

--
Moe Jones
HVAC Service Technician
Energy Equalizers Inc.
Houston, Texas
www.EnergyEqualizers.com

On Aug 30, 2:22 pm, Mike wrote:
Hi everyone.

I have a central air conditioning unit in my ranch-style home (full
basement also). Yesterday the AC just kicked off randomly. I checked
the thermostat and it seemed to be functioning ok (it's digital). I
went downstairs to the power switch dedicated to the central air unit
and turned it off, then back on again. The AC kicked back on, stayed
on and started blowing cool air, then kicked back off again 2 minutes
later.

I suspected there was an airflow problem of some type (filter, etc)
but that doesn't appear to be case, at least not as far as I can
tell.

Are there any other common causes for this type of behavior?

Thank you for any responses,
Mike

Define "kicked off/kicked on". Do you mean the inside unit, the
outside unit, or both. IIRC, all the talk about the compressor
"kicking off" would be related to the outside unit only. If the inside
blower was "kicking off", that would be a whole different problem than
the compressor. At least that's how my residential unit works.

Mike wrote:
Hi everyone.

I have a central air conditioning unit in my ranch-style home (full
basement also). Yesterday the AC just kicked off randomly. I checked
the thermostat and it seemed to be functioning ok (it's digital). I
went downstairs to the power switch dedicated to the central air unit
and turned it off, then back on again. The AC kicked back on, stayed
on and started blowing cool air, then kicked back off again 2 minutes
later.

I suspected there was an airflow problem of some type (filter, etc)
but that doesn't appear to be case, at least not as far as I can
tell.

Are there any other common causes for this type of behavior?

Thank you for any responses,
Mike


If your AC condensing unit is equipped with a low
pressure cut off switch, it can make the unit cut
on and off due to a low freon charge. Unless you
know your way around HVAC systems and have the
proper tools and equipment, you should call someone
who does.

[8~{} Uncle Monster

There are a number of controls in series with the cooling
relay. Anti recycle timer, HP/LP control and compressor
thermal and current Overload.. However the HP control is
normally a manual reset and the LP auto reset so the Unit
as Uncle monster said is probably cycling on the LP control
which indicates a loss of refrigerant charge
"Mike" wrote in message
ups.com...
Hi everyone.

I have a central air conditioning unit in my ranch-style home (full
basement also). Yesterday the AC just kicked off randomly. I checked
the thermostat and it seemed to be functioning ok (it's digital). I
went downstairs to the power switch dedicated to the central air unit
and turned it off, then back on again. The AC kicked back on, stayed
on and started blowing cool air, then kicked back off again 2 minutes
later.

I suspected there was an airflow problem of some type (filter, etc)
but that doesn't appear to be case, at least not as far as I can
tell.

Are there any other common causes for this type of behavior?

Thank you for any responses,
Mike

Telstra wrote:
"Mike" wrote in message
ups.com...
Hi everyone.

I have a central air conditioning unit in my ranch-style home (full
basement also). Yesterday the AC just kicked off randomly. I checked
the thermostat and it seemed to be functioning ok (it's digital). I
went downstairs to the power switch dedicated to the central air unit
and turned it off, then back on again. The AC kicked back on, stayed
on and started blowing cool air, then kicked back off again 2 minutes
later.

I suspected there was an airflow problem of some type (filter, etc)
but that doesn't appear to be case, at least not as far as I can
tell.

Are there any other common causes for this type of behavior?

Thank you for any responses,
Mike


There are a number of controls in series with the cooling
relay. Anti recycle timer, HP/LP control and compressor
thermal and current Overload.. However the HP control is
normally a manual reset and the LP auto reset so the Unit
as Uncle monster said is probably cycling on the LP control
which indicates a loss of refrigerant charge

It's not unusual for me and my guys to add those
controls to a contractor grade condensing unit.
I also add a head pressure control to those AC
systems installed in restaurants since the units
are run year round. If there is no electronic
thermostat with a built in anti-short cycle timer,
an inexpensive timer module installed in the
condensing unit can save an expensive compressor
from those people who like to play with thermostats.
It's often very difficult to convince some folks
to spend money on preventive maintenance.

[8~{} Uncle Monster

On Thu, 30 Aug 2007 17:34:36 -0500, dpb wrote:

Joe wrote:
On Aug 30, 4:49 pm, Mike wrote:

snip

3) Compressor drawing too much current (any way to check this, I do
have a multimeter)

You need an AC ammeter or the right adapter to handle 50 A more or
less on your multimeter. HTH

Quite an adapter to put inline w/ a conventional multimeter...

In a practical sense, unless you have a clampon meter, no, there isn't
an easy way for large currents...typical VOM's are able to handle only a
few 10's of mA.

Some do have a 10A range (with a separate jack). I used to use that
frequently to measure the current use by 120V appliances.
--
Mark Lloyd
http://notstupid.laughingsquid.com

"God was invented by man for a reason, that
reason is no longer applicable."

In article ,
Mark Lloyd wrote:
On Thu, 30 Aug 2007 17:34:36 -0500, dpb wrote:

Joe wrote:
On Aug 30, 4:49 pm, Mike wrote:

snip

3) Compressor drawing too much current (any way to check this, I do
have a multimeter)

You need an AC ammeter or the right adapter to handle 50 A more or
less on your multimeter. HTH

Quite an adapter to put inline w/ a conventional multimeter...

In a practical sense, unless you have a clampon meter, no, there isn't
an easy way for large currents...typical VOM's are able to handle only a
few 10's of mA.

Some do have a 10A range (with a separate jack). I used to use that
frequently to measure the current use by 120V appliances.
--
Mark Lloyd
http://notstupid.laughingsquid.com

"God was invented by man for a reason, that
reason is no longer applicable."


Question: are the clamp-ons at all accurate, or are they
(sometimes) GROSSLY wrong?

EG I got a radio shack 2part vom that had a plug-in clamp-on
coming with it. (maybe $30 when I got it 3 or so yrs ago)

David

On Aug 31, 3:50 am, Uncle Monster wrote:
Telstra wrote:
"Mike" wrote in message
oups.com...
Hi everyone.

I have a central air conditioning unit in my ranch-style home (full
basement also). Yesterday the AC just kicked off randomly. I checked
the thermostat and it seemed to be functioning ok (it's digital). I
went downstairs to the power switch dedicated to the central air unit
and turned it off, then back on again. The AC kicked back on, stayed
on and started blowing cool air, then kicked back off again 2 minutes
later.

I suspected there was an airflow problem of some type (filter, etc)
but that doesn't appear to be case, at least not as far as I can
tell.

Are there any other common causes for this type of behavior?

Thank you for any responses,
Mike

There are a number of controls in series with the cooling
relay. Anti recycle timer, HP/LP control and compressor
thermal and current Overload.. However the HP control is
normally a manual reset and the LP auto reset so the Unit
as Uncle monster said is probably cycling on the LP control
which indicates a loss of refrigerant charge

It's not unusual for me and my guys to add those
controls to a contractor grade condensing unit.
I also add a head pressure control to those AC
systems installed in restaurants since the units
are run year round. If there is no electronic
thermostat with a built in anti-short cycle timer,
an inexpensive timer module installed in the
condensing unit can save an expensive compressor
from those people who like to play with thermostats.
It's often very difficult to convince some folks
to spend money on preventive maintenance.

[8~{} Uncle Monster- Hide quoted text -

- Show quoted text -

If it was low on charge, why would it kick back on and blow cold air?
If you want to be sure that it's not a control problem, remove the
face of the thermostst and install a jumper between the R,G, and Y
terminals. If the A.C. runs continually and cools effectively, replace
the t-stat.

PS: Don't worry, it's only 24volts. Be careful if there is a "C or B"
terminal that you don't touch them with the jumper as you could blow a
transformer fuse.

David Combs wrote:

In article ,
Mark Lloyd wrote:

On Thu, 30 Aug 2007 17:34:36 -0500, dpb wrote:


Joe wrote:

On Aug 30, 4:49 pm, Mike wrote:


snip

3) Compressor drawing too much current (any way to check this, I do
have a multimeter)

You need an AC ammeter or the right adapter to handle 50 A more or
less on your multimeter. HTH

Quite an adapter to put inline w/ a conventional multimeter...

In a practical sense, unless you have a clampon meter, no, there isn't
an easy way for large currents...typical VOM's are able to handle only a
few 10's of mA.

Some do have a 10A range (with a separate jack). I used to use that
frequently to measure the current use by 120V appliances.
--
Mark Lloyd
http://notstupid.laughingsquid.com

"God was invented by man for a reason, that
reason is no longer applicable."



Question: are the clamp-ons at all accurate, or are they
(sometimes) GROSSLY wrong?


Even the $12 ones at Harbor Freight seem to do a pretty good job.

EG I got a radio shack 2part vom that had a plug-in clamp-on
coming with it. (maybe $30 when I got it 3 or so yrs ago)

David




--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

A quality clamp on meter is VERY accurate, and they are used all the time by
professionals to measure current. That's how large currents are measured.
Here are some examples
http://us.fluke.com/usen/products/ca...(FlukeProducts)

A $30 Radio Shack meter could be good or could be bad, but I wouldn't trust
it personally.

--

Mike S.

"David Combs" wrote in message
...

Question: are the clamp-ons at all accurate, or are they
(sometimes) GROSSLY wrong?

EG I got a radio shack 2part vom that had a plug-in clamp-on
coming with it. (maybe $30 when I got it 3 or so yrs ago)

David

Mike S. wrote:

A quality clamp on meter is VERY accurate, and they are used all the time by
professionals to measure current. That's how large currents are measured.
Here are some examples
http://us.fluke.com/usen/products/ca...(FlukeProducts)

A $30 Radio Shack meter could be good or could be bad, but I wouldn't trust
it personally.


It's easy enough to check one out with a known current or by comparison
with an inline meter with a known-good calibration.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .