Part I - The Need for Aux Cooling
Now that Chicago is hitting 100, figured it might be a good time to put some data and thought into our 80’s issues of (over)heat. Since we don’t have a lot of data in regards to things like our Toyota Engine driven Thermo/Fan CFM, RPM and other factors that will help us determine the best cooling method for our trucks, maybe we can look at some of the things we do know about 134a and our A/C systems. For the purpose of discussions of 80 over/heat, I will only address the high pressure side of the A/C system, as it is what creates the heat in the condenser>radiator.
Problem: Many FJ80 owners replace new fan and fan thermostat, still have A/C cutout and overheat. It would appear this is caused by insufficient flow through the condensor and radiator causing heat soak of the condensor in extreme heat environments. Let's look at A/C performance to apply some numbers to the condenser, which in turn might offer some insight into possible solutions.
Toyota FSM lists R134a high pressure readings of 206-213psi as normal (optimal) functioning A/C. 134a has known temps for given pressures. Looking up 206psi pump outlet pressure, we have R134a at 133F. At 213psi we have R134a at 135F. So Toyota dictates the optimal temperature of our hi pressure side for maximum cooling is between 133-135F. Sounds fine, now let’s look at some extremes (high heat, high engine loads, low vehicle speed, low engine speeds) in terms of our 80 specifically.
Toyota pressure switch 866450-01080 (just about every 93>2002 R134a equipped 80/100), uses only the low and high pressure sides for R134a applications (mid range is open on switch - probably used in old R12 system application). Again, assuming properly functioning A/C low side pressures, we are only looking at the high side = high pressure cutout (caused by heat soak of condensor).
FSM (and switch) lists this pressure cutout at 412psi = off, 327psi = on. Back to the charts, that’s 167F = on and 186F = off respectively. Doesn’t seem bad… Except we have a problem that the condenser is most likely not exchanging any heat, since it’s now gained some 50F from it’s ‘normal’ operating function. Since the only heat around that condenser higher is the radiator, we are seeing heat soak from the radiator. Folks, plain and simple, that’s an airflow problem, specifically a lack of one causing heat soak of the condenser core.
I’ve involved myself in some pretty interesting discussions on electric vs engine fans on this forum as of late. It would appear obvious from the numbers above that an 80 that cuts out it’s A/C system is also maxed out on overall engine cooling capacity, because the condenser is heat soaking from the radiator. What to do? There are three ways I see to address this: electric fans replacing engine driven, ducting from engine bay, and/or pusher fan for existing system.
In my own experience and preference to run to redline with my supercharged truck, I prefer to just redo the whole kit and kabootle for several reasons (more to follow as I take on that project). Engine driven fans have a lot of limitations to them, and really have a difficult time handling low engine/vehicle speeds vs high condenser heat (pressure). I won’t go into the lists of our electric options, Summit Racing carries a wide variety that fit our trucks, and Flex-a-lite has a nifty controller that gives adjustability and progressive voltage (speed>cfm). Many junk yards (find the turbo cars!) have some phenomenal cooling with low amp draw that can be had cheap. For the purpose of this post however, let’s look at the advantage of the simplest solution to 80 cooling w A/C, adding an aux ‘pusher’ fan in front of the condenser.
Back to the numbers. From Toyotas published diagnostics we appear to want our A/C condenser temps to be 50-60F below our radiator temps for maximum cooling (195f-60f = 135f). The best way to achieve that (given the engine driven fan) is to put a pusher electric fan in front of the condenser to cool the condenser, because we don’t really directly care about the radiator or engine temps - yet. The radiator heat exchange should be addressed by the Radiator Fan and thermostat, whatever we do to the condenser shouldn’t matter - in fact it should only help. Next up in Part II – wiring options for the aux fan for maximum A/C effectiveness.
Scott Justusson
QSHIPQ Performance Tuning
Chicago IL
94 FZJ80 Supercharger
Now that Chicago is hitting 100, figured it might be a good time to put some data and thought into our 80’s issues of (over)heat. Since we don’t have a lot of data in regards to things like our Toyota Engine driven Thermo/Fan CFM, RPM and other factors that will help us determine the best cooling method for our trucks, maybe we can look at some of the things we do know about 134a and our A/C systems. For the purpose of discussions of 80 over/heat, I will only address the high pressure side of the A/C system, as it is what creates the heat in the condenser>radiator.
Problem: Many FJ80 owners replace new fan and fan thermostat, still have A/C cutout and overheat. It would appear this is caused by insufficient flow through the condensor and radiator causing heat soak of the condensor in extreme heat environments. Let's look at A/C performance to apply some numbers to the condenser, which in turn might offer some insight into possible solutions.
Toyota FSM lists R134a high pressure readings of 206-213psi as normal (optimal) functioning A/C. 134a has known temps for given pressures. Looking up 206psi pump outlet pressure, we have R134a at 133F. At 213psi we have R134a at 135F. So Toyota dictates the optimal temperature of our hi pressure side for maximum cooling is between 133-135F. Sounds fine, now let’s look at some extremes (high heat, high engine loads, low vehicle speed, low engine speeds) in terms of our 80 specifically.
Toyota pressure switch 866450-01080 (just about every 93>2002 R134a equipped 80/100), uses only the low and high pressure sides for R134a applications (mid range is open on switch - probably used in old R12 system application). Again, assuming properly functioning A/C low side pressures, we are only looking at the high side = high pressure cutout (caused by heat soak of condensor).
FSM (and switch) lists this pressure cutout at 412psi = off, 327psi = on. Back to the charts, that’s 167F = on and 186F = off respectively. Doesn’t seem bad… Except we have a problem that the condenser is most likely not exchanging any heat, since it’s now gained some 50F from it’s ‘normal’ operating function. Since the only heat around that condenser higher is the radiator, we are seeing heat soak from the radiator. Folks, plain and simple, that’s an airflow problem, specifically a lack of one causing heat soak of the condenser core.
I’ve involved myself in some pretty interesting discussions on electric vs engine fans on this forum as of late. It would appear obvious from the numbers above that an 80 that cuts out it’s A/C system is also maxed out on overall engine cooling capacity, because the condenser is heat soaking from the radiator. What to do? There are three ways I see to address this: electric fans replacing engine driven, ducting from engine bay, and/or pusher fan for existing system.
In my own experience and preference to run to redline with my supercharged truck, I prefer to just redo the whole kit and kabootle for several reasons (more to follow as I take on that project). Engine driven fans have a lot of limitations to them, and really have a difficult time handling low engine/vehicle speeds vs high condenser heat (pressure). I won’t go into the lists of our electric options, Summit Racing carries a wide variety that fit our trucks, and Flex-a-lite has a nifty controller that gives adjustability and progressive voltage (speed>cfm). Many junk yards (find the turbo cars!) have some phenomenal cooling with low amp draw that can be had cheap. For the purpose of this post however, let’s look at the advantage of the simplest solution to 80 cooling w A/C, adding an aux ‘pusher’ fan in front of the condenser.
Back to the numbers. From Toyotas published diagnostics we appear to want our A/C condenser temps to be 50-60F below our radiator temps for maximum cooling (195f-60f = 135f). The best way to achieve that (given the engine driven fan) is to put a pusher electric fan in front of the condenser to cool the condenser, because we don’t really directly care about the radiator or engine temps - yet. The radiator heat exchange should be addressed by the Radiator Fan and thermostat, whatever we do to the condenser shouldn’t matter - in fact it should only help. Next up in Part II – wiring options for the aux fan for maximum A/C effectiveness.
Scott Justusson
QSHIPQ Performance Tuning
Chicago IL
94 FZJ80 Supercharger
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, but the 10 I had looked too easy
's to our credit?