How cold can you get the A/C in a humid climate???
08-24-2015, 09:13 PM
#1
Racer
Thread Starter
How cold can you get the A/C in a humid climate???
Since I saw another A/C thread that was getting some positive attention, I thought I would throw this out to the experts.....
So I have just rebuilt my A/C in my 89 Carrera 3.2, and it is cold....meaning on the freeway I can cycle at high 30's to low 40's vent temps when it is over 100F degrees outside and 60% humidity....on R134. I am very satisfied.....and yet being one who has a hard time leaving well enough a lone...I have one curiosity I want to try to find an answer to.
My curiosity is this....around town I have to dial up the vent temps to mid 40's at the coldest. If I leave the thermostat set to its coldest possible vent temps that still let the compressor cycle on the freeway......around town the vent temps come down for a period of time, but with stoplights, 45mph and below speeds, etc. the compressor won't cycle nearly as often (if at all), and eventually the vent temps just start rising....up into the mid 60's sometimes. If I catch this, and turn the thermostat to a point where the compressor will cycle a few times regularly often the condition clears a bit. Usually when this happens too I have first on the output line of the evaporator. If there is only wet moisture on it, this never happens.
What I believe is happening is that, since the compressor is not cycling regularly, the evaporator is getting too cold because it does not warm up as it would when the compressor cycles off, and output line of the evaporator is building ice on it. This causes the Expansion Valve (EV) to close and stay closed, causing the temps to go up into the mid 60's (it is trying to fight its icing condition). Now keep in mind my EV and its sensor are open to the air, not covered in cork tape or tar (or what ever that gooey crap is
). I have been told by some that covering both will help prevent the EV's sensor from icing, and give me a little lower temps.
It is my belief that if I lived in Az, or another VERY dry climate, that evap temps well below freezing would be fine. This would be because there is not enough ambient moisture to cause any icing. (Side note - when I live in CA I noticed my other cars A/C dripped very little water. When that same car came here to Florida, it was like a hose was pouring water out of it. This is part of why I have this belief). Here in the lovely swamp of Florida though we have a lot of humidity, which means icing of the system is easier, so we would ideally need to alway run the system where the evaporator and it's output line are above 32F degrees.
Edit: I know my EV is working right (brand new). I know the EV sensor is placed right (brand new, camped at the factory). I know my thermostat is working (brand new, and can cycle normally, as long as I don't crank it too cold).
So I have just rebuilt my A/C in my 89 Carrera 3.2, and it is cold....meaning on the freeway I can cycle at high 30's to low 40's vent temps when it is over 100F degrees outside and 60% humidity....on R134. I am very satisfied.....and yet being one who has a hard time leaving well enough a lone...I have one curiosity I want to try to find an answer to.
My curiosity is this....around town I have to dial up the vent temps to mid 40's at the coldest. If I leave the thermostat set to its coldest possible vent temps that still let the compressor cycle on the freeway......around town the vent temps come down for a period of time, but with stoplights, 45mph and below speeds, etc. the compressor won't cycle nearly as often (if at all), and eventually the vent temps just start rising....up into the mid 60's sometimes. If I catch this, and turn the thermostat to a point where the compressor will cycle a few times regularly often the condition clears a bit. Usually when this happens too I have first on the output line of the evaporator. If there is only wet moisture on it, this never happens.
What I believe is happening is that, since the compressor is not cycling regularly, the evaporator is getting too cold because it does not warm up as it would when the compressor cycles off, and output line of the evaporator is building ice on it. This causes the Expansion Valve (EV) to close and stay closed, causing the temps to go up into the mid 60's (it is trying to fight its icing condition). Now keep in mind my EV and its sensor are open to the air, not covered in cork tape or tar (or what ever that gooey crap is
). I have been told by some that covering both will help prevent the EV's sensor from icing, and give me a little lower temps. It is my belief that if I lived in Az, or another VERY dry climate, that evap temps well below freezing would be fine. This would be because there is not enough ambient moisture to cause any icing. (Side note - when I live in CA I noticed my other cars A/C dripped very little water. When that same car came here to Florida, it was like a hose was pouring water out of it. This is part of why I have this belief). Here in the lovely swamp of Florida though we have a lot of humidity, which means icing of the system is easier, so we would ideally need to alway run the system where the evaporator and it's output line are above 32F degrees.
- Do the experts here think insulating the EV sensor (and the valve?) would help this a bit?
- Do the experts here think that, all things being equal, colder evep temps...and therefor colder vent temps..... are possible in very dry climates vs. very humid climates?
Edit: I know my EV is working right (brand new). I know the EV sensor is placed right (brand new, camped at the factory). I know my thermostat is working (brand new, and can cycle normally, as long as I don't crank it too cold).
08-25-2015, 01:32 PM
#2
Drifting
"EV" = Expansion Valve, TXV/TEV..??
"EV sensor = expansion valve pigtail sensor?
If both are correct, then yes, the pigtail sensor should most definitely be insulated.
Insulated expansion valve, no need.
You imply that "on the road" you can adjust the A/C set point to less than COLDEST and still be comfortable. On the other hand in situations wherein the engine RPM is consistently low you must adjust the setting to "COLDEST", maximum cooling, and risk freeze up, in order to keep the cabin at/near your comfort level.
I suspect that what you are experiencing is SOP for our cars with only the factory system.
What I suspect is that the system is struggling mightily to keep up with demand.
The compressor is running full time, never cycling off, because the TXV is being starved of liquid refrigerant thereby resulting in the evaporator being CHILLED near the TXV outflow area ONLY.
The coolness never propagates to the area into which the thermostatic switch's capillary sensor is chilled enough to cycle the compressor off and the area nearest the evaporator inlet begins to freeze up as a result of that area being at sub-freezing temperature.
As that area freezes up the ice provides insulation against the "HOT" blower airflow and now the "freeze" begins to propagate to the area beyond the frozen "section".
The higher the local Rh the more rapidly the freeze up will propagate throughout the evaporator CSA.
Strange as it may seem if the system could provide MORE cooling capacity then these freeze-up instances would be less likely to happen.
With enough liquid supply to the TXV it could FLOOD the evaporator and thereby spread the refrigerant's CHILLING effect throughout the evaporator, not just nearest the TXV, the thermostatic switch's capillary sensor would then operate normally provided it were "calibrated" such that the on/off span average temperature is slightly above freezing, 33-34dF.
The very best fix that I know of for the moment would be the addition of condenser capacity via ZIM's fender well condenser/fan KIT, $500.
In the meantime leaving the control at the "on the road" position is the best solution.
Once, if, some aftermarket vendor provides a kit equal to ZIM's but using a more efficient, dramatically so, parallel flow condenser, I would be one of the first to buy in, in hopes of eliminating the problematic engine lid condenser.
"EV sensor = expansion valve pigtail sensor?
If both are correct, then yes, the pigtail sensor should most definitely be insulated.
Insulated expansion valve, no need.
You imply that "on the road" you can adjust the A/C set point to less than COLDEST and still be comfortable. On the other hand in situations wherein the engine RPM is consistently low you must adjust the setting to "COLDEST", maximum cooling, and risk freeze up, in order to keep the cabin at/near your comfort level.
I suspect that what you are experiencing is SOP for our cars with only the factory system.
What I suspect is that the system is struggling mightily to keep up with demand.
The compressor is running full time, never cycling off, because the TXV is being starved of liquid refrigerant thereby resulting in the evaporator being CHILLED near the TXV outflow area ONLY.
The coolness never propagates to the area into which the thermostatic switch's capillary sensor is chilled enough to cycle the compressor off and the area nearest the evaporator inlet begins to freeze up as a result of that area being at sub-freezing temperature.
As that area freezes up the ice provides insulation against the "HOT" blower airflow and now the "freeze" begins to propagate to the area beyond the frozen "section".
The higher the local Rh the more rapidly the freeze up will propagate throughout the evaporator CSA.
Strange as it may seem if the system could provide MORE cooling capacity then these freeze-up instances would be less likely to happen.
With enough liquid supply to the TXV it could FLOOD the evaporator and thereby spread the refrigerant's CHILLING effect throughout the evaporator, not just nearest the TXV, the thermostatic switch's capillary sensor would then operate normally provided it were "calibrated" such that the on/off span average temperature is slightly above freezing, 33-34dF.
The very best fix that I know of for the moment would be the addition of condenser capacity via ZIM's fender well condenser/fan KIT, $500.
In the meantime leaving the control at the "on the road" position is the best solution.
Once, if, some aftermarket vendor provides a kit equal to ZIM's but using a more efficient, dramatically so, parallel flow condenser, I would be one of the first to buy in, in hopes of eliminating the problematic engine lid condenser.
Last edited by wwest; 08-26-2015 at 03:05 PM.
08-25-2015, 03:14 PM
#3
Racer
Thread Starter
"EV" = Expansion Valve, TXV/TEV..??
"EV sensor = expansion valve pigtail sensor?
If both are correct, then yes, the pigtail sensor should most definitely be insulated.
Insulated expansion valve, no need.
You imply that "on the road" you can adjust the A/C set point to less than COLDEST and still be comfortable. On the other hand in situations wherein the engine RPM is consistently low you must adjust the setting to "COLDEST", maximum cooling, and risk freeze up, in order to keep the cabin at/near your comfort level.
I suspect that what you are experiencing is SOP for our cars with only the factory system.
What I suspect is that the system is struggling mightily to keep up with demand.
The compressor is running full time, never cycling off, because the TXV is being starved of liquid refrigerant thereby resulting in the evaporator being CHILLED near the TXV outflow area ONLY.
The coolness never propagates to the area into which the thermostatic switch's capillary sensor is chilled enough to cycle the compressor off and the area nearest the evaporator begins to freeze up as a result of that area being at sub-freezing temperature.
As that area freezes up the ice provides insulation against the "HOT" blower airflow and now the "freeze" begins to propagate to the area beyond the frozen "section".
The higher the local Rh the more rapidly the freeze up will propagate throughout the evaporator CSA.
Strange as it may seem if the system could provide MORE cooling capacity then these freeze-up instances would be less likely to happen.
With enough liquid supply to the TXV it could FLOOD the evaporator and thereby spread the refrigerant's CHILLING effect throughout the evaporator, not just nearest the TXV, the thermostatic switch's capillary sensor would then operate normally provided it were "calibrated" such that the on/off span average temperature is slightly above freezing, 33-34dF.
The very best fix that I know of for the moment would be the addition of condenser capacity via ZIM's fender well condenser/fan KIT, $500.
In the meantime leaving the control at the "on the road" position is the best solution.
Once, if, some aftermarket vendor provides a kit equal to ZIM's but using a more efficient, dramatically so, parallel flow condenser, I would be one of the first to buy in, in hopes of eliminating the problematic engine lid condenser.
"EV sensor = expansion valve pigtail sensor?
If both are correct, then yes, the pigtail sensor should most definitely be insulated.
Insulated expansion valve, no need.
You imply that "on the road" you can adjust the A/C set point to less than COLDEST and still be comfortable. On the other hand in situations wherein the engine RPM is consistently low you must adjust the setting to "COLDEST", maximum cooling, and risk freeze up, in order to keep the cabin at/near your comfort level.
I suspect that what you are experiencing is SOP for our cars with only the factory system.
What I suspect is that the system is struggling mightily to keep up with demand.
The compressor is running full time, never cycling off, because the TXV is being starved of liquid refrigerant thereby resulting in the evaporator being CHILLED near the TXV outflow area ONLY.
The coolness never propagates to the area into which the thermostatic switch's capillary sensor is chilled enough to cycle the compressor off and the area nearest the evaporator begins to freeze up as a result of that area being at sub-freezing temperature.
As that area freezes up the ice provides insulation against the "HOT" blower airflow and now the "freeze" begins to propagate to the area beyond the frozen "section".
The higher the local Rh the more rapidly the freeze up will propagate throughout the evaporator CSA.
Strange as it may seem if the system could provide MORE cooling capacity then these freeze-up instances would be less likely to happen.
With enough liquid supply to the TXV it could FLOOD the evaporator and thereby spread the refrigerant's CHILLING effect throughout the evaporator, not just nearest the TXV, the thermostatic switch's capillary sensor would then operate normally provided it were "calibrated" such that the on/off span average temperature is slightly above freezing, 33-34dF.
The very best fix that I know of for the moment would be the addition of condenser capacity via ZIM's fender well condenser/fan KIT, $500.
In the meantime leaving the control at the "on the road" position is the best solution.
Once, if, some aftermarket vendor provides a kit equal to ZIM's but using a more efficient, dramatically so, parallel flow condenser, I would be one of the first to buy in, in hopes of eliminating the problematic engine lid condenser.
My system though is far from stock. I have almost the full RetroAir system, AND a 625cfm fan on the rear condenser. The RetoAir rear condenser is a great Multiflow condenser.
I will insulate the pigtail sensor and report back. My belief is that the pigtail being insulted, and moving my thermostats sensor in the eval will help a lot.
My main questions still remains....how cold can you get the evap in a humid climate? Am I correct that 32 is about it given the high Rh....vs in a place like Az (with single digit Rh) you could go below freezing?
08-26-2015, 02:56 PM
#4
Drifting
You were correct on both eh EV and the EV Sensor.
My system though is far from stock. I have almost the full RetroAir system, AND a 625cfm fan on the rear condenser. The RetoAir rear condenser is a great Multiflow condenser.
IIRC the engine lid PFC is the ONLY condenser in your system...
I will insulate the pigtail sensor and report back. My belief is that the pigtail being insulted, and moving my thermostats sensor in the eval will help a lot.
I believe the thermostat's capillary sensor is best placed nearest the outflow point in the case of a serpentine evaporator. Someone else may know for certain.
My main questions still remains....how cold can you get the evap in a humid climate? Am I correct that 32 is about it given the high Rh....vs in a place like Az (with single digit Rh) you could go below freezing?
My system though is far from stock. I have almost the full RetroAir system, AND a 625cfm fan on the rear condenser. The RetoAir rear condenser is a great Multiflow condenser.
IIRC the engine lid PFC is the ONLY condenser in your system...
I will insulate the pigtail sensor and report back. My belief is that the pigtail being insulted, and moving my thermostats sensor in the eval will help a lot.
I believe the thermostat's capillary sensor is best placed nearest the outflow point in the case of a serpentine evaporator. Someone else may know for certain.
My main questions still remains....how cold can you get the evap in a humid climate? Am I correct that 32 is about it given the high Rh....vs in a place like Az (with single digit Rh) you could go below freezing?
But, even in a high Rh climate the icing up period may be long since our cars have no "forced" fresh, HUMID, air intake.