TJ A/C Issues
06-18-2007, 10:22 AM
#21
Guest
Posts: n/a
Re: TJ A/C Issues
On Jun 16, 12:38 am, Richard J Kinch <k...@truetex.com> wrote:
> Joe writes:
> > Does anyone on here have any suggestions on other things to check?
>
> You may have an incompetent repairman. Ice anywhere on an A/C system is
> solid evidence of malfunction.
>
> Replacing hoses to fix icing?!?!?! Who swindled you on that?
>
> A refrigerant undercharge is (paradoxically) one cause of icing. An
> undercharge will also behave as you describe, working OK in light loads,
> but not keeping up with more heat and/or humidity. So will a
> restriction in the system.
>
> Why was the low-pressure switch replaced? More guessing at your
> expense?
>
> When you have the evaporator and accumulator replaced, you should have
> demanded a vacuum leak test, where you actually personally get to watch
> the gages and see them hold a vacuum. So many A/C techs are incompetent
> or will wave off a slow leak because they make believe it is fixed or
> won't matter.
>
> If you've paid as much as I think you have for this work, then you
> should have been shown performance test results per the service manual.
> None of this wave-of-the-hand-your-done.
>
> A/C work is absolutely the worst to hire out. Huge prices for guys who
> pretend to know something they don't. That's why I learned to do it all
> myself.
Just curious, could any of those replaced components (evaporator,
accumulator, etc.) been damaged by a chronic undercharge of the system
(excessive and constant freezing up of system for probably 2 years)?
I try to keep my car in nearly perfect condition, and this issue was
misdiagnosed so many times that it persisted as the freezing problem
continued for quite a while. I just want to make sure those parts
were not compromised *because* the shop dismissed the problems for so
long, in which case, making the responsible for their failure. Thanks
again.
Joe
> Joe writes:
> > Does anyone on here have any suggestions on other things to check?
>
> You may have an incompetent repairman. Ice anywhere on an A/C system is
> solid evidence of malfunction.
>
> Replacing hoses to fix icing?!?!?! Who swindled you on that?
>
> A refrigerant undercharge is (paradoxically) one cause of icing. An
> undercharge will also behave as you describe, working OK in light loads,
> but not keeping up with more heat and/or humidity. So will a
> restriction in the system.
>
> Why was the low-pressure switch replaced? More guessing at your
> expense?
>
> When you have the evaporator and accumulator replaced, you should have
> demanded a vacuum leak test, where you actually personally get to watch
> the gages and see them hold a vacuum. So many A/C techs are incompetent
> or will wave off a slow leak because they make believe it is fixed or
> won't matter.
>
> If you've paid as much as I think you have for this work, then you
> should have been shown performance test results per the service manual.
> None of this wave-of-the-hand-your-done.
>
> A/C work is absolutely the worst to hire out. Huge prices for guys who
> pretend to know something they don't. That's why I learned to do it all
> myself.
Just curious, could any of those replaced components (evaporator,
accumulator, etc.) been damaged by a chronic undercharge of the system
(excessive and constant freezing up of system for probably 2 years)?
I try to keep my car in nearly perfect condition, and this issue was
misdiagnosed so many times that it persisted as the freezing problem
continued for quite a while. I just want to make sure those parts
were not compromised *because* the shop dismissed the problems for so
long, in which case, making the responsible for their failure. Thanks
again.
Joe
06-18-2007, 11:57 AM
#22
Guest
Posts: n/a
Re: TJ A/C Issues
On Sat, 16 Jun 2007 03:07:44 -0000, Joe <UMparrothead@gmail.com>
wrote:
>Does anyone on here have any suggestions on other things to check?
>Since the summer is in full swing, I'd really like to get this A/C
>problem finally fixed. Thanks for anything you've got.
One thing that can help A/C output overall is to shutoff water flow to
heater core in summer (Lowes sells some in line ball valves that do
nicely when adapted to this here) The reason for this is not most car
simply try to route air around heater core in hot weather but the 200
plus cores is still in there on a hot day radiating heat into ducts.
This is why when you shut your car off on a hot day for a while and
then start it up it blows hot air for a while from A/C vents because
the hot core heat soaks the whole A/C and heater box when you shut it
down. I have done this to all my SUV's. It helps the air be a bit
cold overall as well because the ducts doors and such leak with age
and shutting off the hot water cures this leakage for good. You will
notice first time you hot start it after it sits for a bit that there
will be no blast of hot air from vents for heater core cooking ducts
and A/C will work better in recirculate mode too because there will be
no hot spots in the ductwork to warm air and full capacity will go to
cooling car. I can run my truck in 90 plus weather, blowing snow
flakes so to speak, stop for a while and then start it back up and no
heat soaked blast and have full cooling in a matter of seconds. You
may have some other issues but it kinda sounds to me the you may have
some heater door leakage and heat soak because the hotter it gets the
hotter the coolant is going to tend to get and the more it is going to
warm your air in ducts. Long ago they used to shut water flow off on a
lot of vehcile when heat was not on and A/C was selected but to save
prodcution costs they did away with that long ago. (back in 1990 GM
even issued a service bulletin for 89 burbs like mine that added a
water cutoff valve to heater core curcuit during A/C max operation
because of door/baffle leakage on some models.
-----------------
TheSnoMan.com
wrote:
>Does anyone on here have any suggestions on other things to check?
>Since the summer is in full swing, I'd really like to get this A/C
>problem finally fixed. Thanks for anything you've got.
One thing that can help A/C output overall is to shutoff water flow to
heater core in summer (Lowes sells some in line ball valves that do
nicely when adapted to this here) The reason for this is not most car
simply try to route air around heater core in hot weather but the 200
plus cores is still in there on a hot day radiating heat into ducts.
This is why when you shut your car off on a hot day for a while and
then start it up it blows hot air for a while from A/C vents because
the hot core heat soaks the whole A/C and heater box when you shut it
down. I have done this to all my SUV's. It helps the air be a bit
cold overall as well because the ducts doors and such leak with age
and shutting off the hot water cures this leakage for good. You will
notice first time you hot start it after it sits for a bit that there
will be no blast of hot air from vents for heater core cooking ducts
and A/C will work better in recirculate mode too because there will be
no hot spots in the ductwork to warm air and full capacity will go to
cooling car. I can run my truck in 90 plus weather, blowing snow
flakes so to speak, stop for a while and then start it back up and no
heat soaked blast and have full cooling in a matter of seconds. You
may have some other issues but it kinda sounds to me the you may have
some heater door leakage and heat soak because the hotter it gets the
hotter the coolant is going to tend to get and the more it is going to
warm your air in ducts. Long ago they used to shut water flow off on a
lot of vehcile when heat was not on and A/C was selected but to save
prodcution costs they did away with that long ago. (back in 1990 GM
even issued a service bulletin for 89 burbs like mine that added a
water cutoff valve to heater core curcuit during A/C max operation
because of door/baffle leakage on some models.
-----------------
TheSnoMan.com
06-18-2007, 11:57 AM
#23
Guest
Posts: n/a
Re: TJ A/C Issues
On Sat, 16 Jun 2007 03:07:44 -0000, Joe <UMparrothead@gmail.com>
wrote:
>Does anyone on here have any suggestions on other things to check?
>Since the summer is in full swing, I'd really like to get this A/C
>problem finally fixed. Thanks for anything you've got.
One thing that can help A/C output overall is to shutoff water flow to
heater core in summer (Lowes sells some in line ball valves that do
nicely when adapted to this here) The reason for this is not most car
simply try to route air around heater core in hot weather but the 200
plus cores is still in there on a hot day radiating heat into ducts.
This is why when you shut your car off on a hot day for a while and
then start it up it blows hot air for a while from A/C vents because
the hot core heat soaks the whole A/C and heater box when you shut it
down. I have done this to all my SUV's. It helps the air be a bit
cold overall as well because the ducts doors and such leak with age
and shutting off the hot water cures this leakage for good. You will
notice first time you hot start it after it sits for a bit that there
will be no blast of hot air from vents for heater core cooking ducts
and A/C will work better in recirculate mode too because there will be
no hot spots in the ductwork to warm air and full capacity will go to
cooling car. I can run my truck in 90 plus weather, blowing snow
flakes so to speak, stop for a while and then start it back up and no
heat soaked blast and have full cooling in a matter of seconds. You
may have some other issues but it kinda sounds to me the you may have
some heater door leakage and heat soak because the hotter it gets the
hotter the coolant is going to tend to get and the more it is going to
warm your air in ducts. Long ago they used to shut water flow off on a
lot of vehcile when heat was not on and A/C was selected but to save
prodcution costs they did away with that long ago. (back in 1990 GM
even issued a service bulletin for 89 burbs like mine that added a
water cutoff valve to heater core curcuit during A/C max operation
because of door/baffle leakage on some models.
-----------------
TheSnoMan.com
wrote:
>Does anyone on here have any suggestions on other things to check?
>Since the summer is in full swing, I'd really like to get this A/C
>problem finally fixed. Thanks for anything you've got.
One thing that can help A/C output overall is to shutoff water flow to
heater core in summer (Lowes sells some in line ball valves that do
nicely when adapted to this here) The reason for this is not most car
simply try to route air around heater core in hot weather but the 200
plus cores is still in there on a hot day radiating heat into ducts.
This is why when you shut your car off on a hot day for a while and
then start it up it blows hot air for a while from A/C vents because
the hot core heat soaks the whole A/C and heater box when you shut it
down. I have done this to all my SUV's. It helps the air be a bit
cold overall as well because the ducts doors and such leak with age
and shutting off the hot water cures this leakage for good. You will
notice first time you hot start it after it sits for a bit that there
will be no blast of hot air from vents for heater core cooking ducts
and A/C will work better in recirculate mode too because there will be
no hot spots in the ductwork to warm air and full capacity will go to
cooling car. I can run my truck in 90 plus weather, blowing snow
flakes so to speak, stop for a while and then start it back up and no
heat soaked blast and have full cooling in a matter of seconds. You
may have some other issues but it kinda sounds to me the you may have
some heater door leakage and heat soak because the hotter it gets the
hotter the coolant is going to tend to get and the more it is going to
warm your air in ducts. Long ago they used to shut water flow off on a
lot of vehcile when heat was not on and A/C was selected but to save
prodcution costs they did away with that long ago. (back in 1990 GM
even issued a service bulletin for 89 burbs like mine that added a
water cutoff valve to heater core curcuit during A/C max operation
because of door/baffle leakage on some models.
-----------------
TheSnoMan.com
06-18-2007, 11:57 AM
#24
Guest
Posts: n/a
Re: TJ A/C Issues
On Sat, 16 Jun 2007 03:07:44 -0000, Joe <UMparrothead@gmail.com>
wrote:
>Does anyone on here have any suggestions on other things to check?
>Since the summer is in full swing, I'd really like to get this A/C
>problem finally fixed. Thanks for anything you've got.
One thing that can help A/C output overall is to shutoff water flow to
heater core in summer (Lowes sells some in line ball valves that do
nicely when adapted to this here) The reason for this is not most car
simply try to route air around heater core in hot weather but the 200
plus cores is still in there on a hot day radiating heat into ducts.
This is why when you shut your car off on a hot day for a while and
then start it up it blows hot air for a while from A/C vents because
the hot core heat soaks the whole A/C and heater box when you shut it
down. I have done this to all my SUV's. It helps the air be a bit
cold overall as well because the ducts doors and such leak with age
and shutting off the hot water cures this leakage for good. You will
notice first time you hot start it after it sits for a bit that there
will be no blast of hot air from vents for heater core cooking ducts
and A/C will work better in recirculate mode too because there will be
no hot spots in the ductwork to warm air and full capacity will go to
cooling car. I can run my truck in 90 plus weather, blowing snow
flakes so to speak, stop for a while and then start it back up and no
heat soaked blast and have full cooling in a matter of seconds. You
may have some other issues but it kinda sounds to me the you may have
some heater door leakage and heat soak because the hotter it gets the
hotter the coolant is going to tend to get and the more it is going to
warm your air in ducts. Long ago they used to shut water flow off on a
lot of vehcile when heat was not on and A/C was selected but to save
prodcution costs they did away with that long ago. (back in 1990 GM
even issued a service bulletin for 89 burbs like mine that added a
water cutoff valve to heater core curcuit during A/C max operation
because of door/baffle leakage on some models.
-----------------
TheSnoMan.com
wrote:
>Does anyone on here have any suggestions on other things to check?
>Since the summer is in full swing, I'd really like to get this A/C
>problem finally fixed. Thanks for anything you've got.
One thing that can help A/C output overall is to shutoff water flow to
heater core in summer (Lowes sells some in line ball valves that do
nicely when adapted to this here) The reason for this is not most car
simply try to route air around heater core in hot weather but the 200
plus cores is still in there on a hot day radiating heat into ducts.
This is why when you shut your car off on a hot day for a while and
then start it up it blows hot air for a while from A/C vents because
the hot core heat soaks the whole A/C and heater box when you shut it
down. I have done this to all my SUV's. It helps the air be a bit
cold overall as well because the ducts doors and such leak with age
and shutting off the hot water cures this leakage for good. You will
notice first time you hot start it after it sits for a bit that there
will be no blast of hot air from vents for heater core cooking ducts
and A/C will work better in recirculate mode too because there will be
no hot spots in the ductwork to warm air and full capacity will go to
cooling car. I can run my truck in 90 plus weather, blowing snow
flakes so to speak, stop for a while and then start it back up and no
heat soaked blast and have full cooling in a matter of seconds. You
may have some other issues but it kinda sounds to me the you may have
some heater door leakage and heat soak because the hotter it gets the
hotter the coolant is going to tend to get and the more it is going to
warm your air in ducts. Long ago they used to shut water flow off on a
lot of vehcile when heat was not on and A/C was selected but to save
prodcution costs they did away with that long ago. (back in 1990 GM
even issued a service bulletin for 89 burbs like mine that added a
water cutoff valve to heater core curcuit during A/C max operation
because of door/baffle leakage on some models.
-----------------
TheSnoMan.com
06-18-2007, 11:57 AM
#25
Guest
Posts: n/a
Re: TJ A/C Issues
On Sat, 16 Jun 2007 03:07:44 -0000, Joe <UMparrothead@gmail.com>
wrote:
>Does anyone on here have any suggestions on other things to check?
>Since the summer is in full swing, I'd really like to get this A/C
>problem finally fixed. Thanks for anything you've got.
One thing that can help A/C output overall is to shutoff water flow to
heater core in summer (Lowes sells some in line ball valves that do
nicely when adapted to this here) The reason for this is not most car
simply try to route air around heater core in hot weather but the 200
plus cores is still in there on a hot day radiating heat into ducts.
This is why when you shut your car off on a hot day for a while and
then start it up it blows hot air for a while from A/C vents because
the hot core heat soaks the whole A/C and heater box when you shut it
down. I have done this to all my SUV's. It helps the air be a bit
cold overall as well because the ducts doors and such leak with age
and shutting off the hot water cures this leakage for good. You will
notice first time you hot start it after it sits for a bit that there
will be no blast of hot air from vents for heater core cooking ducts
and A/C will work better in recirculate mode too because there will be
no hot spots in the ductwork to warm air and full capacity will go to
cooling car. I can run my truck in 90 plus weather, blowing snow
flakes so to speak, stop for a while and then start it back up and no
heat soaked blast and have full cooling in a matter of seconds. You
may have some other issues but it kinda sounds to me the you may have
some heater door leakage and heat soak because the hotter it gets the
hotter the coolant is going to tend to get and the more it is going to
warm your air in ducts. Long ago they used to shut water flow off on a
lot of vehcile when heat was not on and A/C was selected but to save
prodcution costs they did away with that long ago. (back in 1990 GM
even issued a service bulletin for 89 burbs like mine that added a
water cutoff valve to heater core curcuit during A/C max operation
because of door/baffle leakage on some models.
-----------------
TheSnoMan.com
wrote:
>Does anyone on here have any suggestions on other things to check?
>Since the summer is in full swing, I'd really like to get this A/C
>problem finally fixed. Thanks for anything you've got.
One thing that can help A/C output overall is to shutoff water flow to
heater core in summer (Lowes sells some in line ball valves that do
nicely when adapted to this here) The reason for this is not most car
simply try to route air around heater core in hot weather but the 200
plus cores is still in there on a hot day radiating heat into ducts.
This is why when you shut your car off on a hot day for a while and
then start it up it blows hot air for a while from A/C vents because
the hot core heat soaks the whole A/C and heater box when you shut it
down. I have done this to all my SUV's. It helps the air be a bit
cold overall as well because the ducts doors and such leak with age
and shutting off the hot water cures this leakage for good. You will
notice first time you hot start it after it sits for a bit that there
will be no blast of hot air from vents for heater core cooking ducts
and A/C will work better in recirculate mode too because there will be
no hot spots in the ductwork to warm air and full capacity will go to
cooling car. I can run my truck in 90 plus weather, blowing snow
flakes so to speak, stop for a while and then start it back up and no
heat soaked blast and have full cooling in a matter of seconds. You
may have some other issues but it kinda sounds to me the you may have
some heater door leakage and heat soak because the hotter it gets the
hotter the coolant is going to tend to get and the more it is going to
warm your air in ducts. Long ago they used to shut water flow off on a
lot of vehcile when heat was not on and A/C was selected but to save
prodcution costs they did away with that long ago. (back in 1990 GM
even issued a service bulletin for 89 burbs like mine that added a
water cutoff valve to heater core curcuit during A/C max operation
because of door/baffle leakage on some models.
-----------------
TheSnoMan.com
06-18-2007, 03:51 PM
#26
Guest
Posts: n/a
Re: TJ A/C Issues
Joe writes:
> Just curious, could any of those replaced components (evaporator,
> accumulator, etc.) been damaged by a chronic undercharge of the system
> (excessive and constant freezing up of system for probably 2 years)?
Not likely.
With undercharge you can get below atmospheric pressure conditions in the
system which pulls in (moist) ambient air if there are leaks. The
accumulator contains a dessicant packet to absorb any moisture. The
dessicant can be saturated if enough moisture is introduced, but that's
quite a lot.
Freezing doesn't usually cause ice-expansion damage, if that's what you're
worried about, since the ice is typically building up from sublimated water
vapor, not liquid water. This is how your household "frost free"
refrigerator-freezer works, building up frost on the evaporator which must
be defrosted with an automatic heating cycle once or twice a day.
> Just curious, could any of those replaced components (evaporator,
> accumulator, etc.) been damaged by a chronic undercharge of the system
> (excessive and constant freezing up of system for probably 2 years)?
Not likely.
With undercharge you can get below atmospheric pressure conditions in the
system which pulls in (moist) ambient air if there are leaks. The
accumulator contains a dessicant packet to absorb any moisture. The
dessicant can be saturated if enough moisture is introduced, but that's
quite a lot.
Freezing doesn't usually cause ice-expansion damage, if that's what you're
worried about, since the ice is typically building up from sublimated water
vapor, not liquid water. This is how your household "frost free"
refrigerator-freezer works, building up frost on the evaporator which must
be defrosted with an automatic heating cycle once or twice a day.
06-18-2007, 03:51 PM
#27
Guest
Posts: n/a
Re: TJ A/C Issues
Joe writes:
> Just curious, could any of those replaced components (evaporator,
> accumulator, etc.) been damaged by a chronic undercharge of the system
> (excessive and constant freezing up of system for probably 2 years)?
Not likely.
With undercharge you can get below atmospheric pressure conditions in the
system which pulls in (moist) ambient air if there are leaks. The
accumulator contains a dessicant packet to absorb any moisture. The
dessicant can be saturated if enough moisture is introduced, but that's
quite a lot.
Freezing doesn't usually cause ice-expansion damage, if that's what you're
worried about, since the ice is typically building up from sublimated water
vapor, not liquid water. This is how your household "frost free"
refrigerator-freezer works, building up frost on the evaporator which must
be defrosted with an automatic heating cycle once or twice a day.
> Just curious, could any of those replaced components (evaporator,
> accumulator, etc.) been damaged by a chronic undercharge of the system
> (excessive and constant freezing up of system for probably 2 years)?
Not likely.
With undercharge you can get below atmospheric pressure conditions in the
system which pulls in (moist) ambient air if there are leaks. The
accumulator contains a dessicant packet to absorb any moisture. The
dessicant can be saturated if enough moisture is introduced, but that's
quite a lot.
Freezing doesn't usually cause ice-expansion damage, if that's what you're
worried about, since the ice is typically building up from sublimated water
vapor, not liquid water. This is how your household "frost free"
refrigerator-freezer works, building up frost on the evaporator which must
be defrosted with an automatic heating cycle once or twice a day.
06-18-2007, 03:51 PM
#28
Guest
Posts: n/a
Re: TJ A/C Issues
Joe writes:
> Just curious, could any of those replaced components (evaporator,
> accumulator, etc.) been damaged by a chronic undercharge of the system
> (excessive and constant freezing up of system for probably 2 years)?
Not likely.
With undercharge you can get below atmospheric pressure conditions in the
system which pulls in (moist) ambient air if there are leaks. The
accumulator contains a dessicant packet to absorb any moisture. The
dessicant can be saturated if enough moisture is introduced, but that's
quite a lot.
Freezing doesn't usually cause ice-expansion damage, if that's what you're
worried about, since the ice is typically building up from sublimated water
vapor, not liquid water. This is how your household "frost free"
refrigerator-freezer works, building up frost on the evaporator which must
be defrosted with an automatic heating cycle once or twice a day.
> Just curious, could any of those replaced components (evaporator,
> accumulator, etc.) been damaged by a chronic undercharge of the system
> (excessive and constant freezing up of system for probably 2 years)?
Not likely.
With undercharge you can get below atmospheric pressure conditions in the
system which pulls in (moist) ambient air if there are leaks. The
accumulator contains a dessicant packet to absorb any moisture. The
dessicant can be saturated if enough moisture is introduced, but that's
quite a lot.
Freezing doesn't usually cause ice-expansion damage, if that's what you're
worried about, since the ice is typically building up from sublimated water
vapor, not liquid water. This is how your household "frost free"
refrigerator-freezer works, building up frost on the evaporator which must
be defrosted with an automatic heating cycle once or twice a day.
06-18-2007, 03:51 PM
#29
Guest
Posts: n/a
Re: TJ A/C Issues
Joe writes:
> Just curious, could any of those replaced components (evaporator,
> accumulator, etc.) been damaged by a chronic undercharge of the system
> (excessive and constant freezing up of system for probably 2 years)?
Not likely.
With undercharge you can get below atmospheric pressure conditions in the
system which pulls in (moist) ambient air if there are leaks. The
accumulator contains a dessicant packet to absorb any moisture. The
dessicant can be saturated if enough moisture is introduced, but that's
quite a lot.
Freezing doesn't usually cause ice-expansion damage, if that's what you're
worried about, since the ice is typically building up from sublimated water
vapor, not liquid water. This is how your household "frost free"
refrigerator-freezer works, building up frost on the evaporator which must
be defrosted with an automatic heating cycle once or twice a day.
> Just curious, could any of those replaced components (evaporator,
> accumulator, etc.) been damaged by a chronic undercharge of the system
> (excessive and constant freezing up of system for probably 2 years)?
Not likely.
With undercharge you can get below atmospheric pressure conditions in the
system which pulls in (moist) ambient air if there are leaks. The
accumulator contains a dessicant packet to absorb any moisture. The
dessicant can be saturated if enough moisture is introduced, but that's
quite a lot.
Freezing doesn't usually cause ice-expansion damage, if that's what you're
worried about, since the ice is typically building up from sublimated water
vapor, not liquid water. This is how your household "frost free"
refrigerator-freezer works, building up frost on the evaporator which must
be defrosted with an automatic heating cycle once or twice a day.
06-18-2007, 07:27 PM
#30
Guest
Posts: n/a
Re: Re: TJ A/C Issues
On Mon, 18 Jun 2007 14:51:49 -0500, Richard J Kinch
<kinch@truetex.com> wrote:
>With undercharge you can get below atmospheric pressure conditions in the
>system which pulls in (moist) ambient air if there are leaks. The
>accumulator contains a dessicant packet to absorb any moisture. The
>dessicant can be saturated if enough moisture is introduced, but that's
>quite a lot.
Never happen, the low pressure cutout switch would kick in long before
you even came close to negative pressure. It could MAYBE happen in
theory if you had a very very low charge and a bypassed low pressure
switch but even then the expansion orifice would limit the pressure
differentail and keep it from going very far negative and also pump
would sieze soon to because with not refrigerant curculating their
would be no lube for compressor (this is one reason for low pressure
cutout switch)
-----------------
TheSnoMan.com
<kinch@truetex.com> wrote:
>With undercharge you can get below atmospheric pressure conditions in the
>system which pulls in (moist) ambient air if there are leaks. The
>accumulator contains a dessicant packet to absorb any moisture. The
>dessicant can be saturated if enough moisture is introduced, but that's
>quite a lot.
Never happen, the low pressure cutout switch would kick in long before
you even came close to negative pressure. It could MAYBE happen in
theory if you had a very very low charge and a bypassed low pressure
switch but even then the expansion orifice would limit the pressure
differentail and keep it from going very far negative and also pump
would sieze soon to because with not refrigerant curculating their
would be no lube for compressor (this is one reason for low pressure
cutout switch)
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