2004 Accord and 2011 Civic, evap freezing on both

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ScottNC
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2004 Accord and 2011 Civic, evap freezing on both

Post by ScottNC »

Wife's cars, I drive 440K mile junk. The '04 is a garage queen with less than 90K+ on it, the '11 has just over 200K. Neither car has had so much as the AC service port caps off. Both exhibit the same symptom: Good cold air for a couple hours then the not so cold and the air gets a bit stuffy. Shut the AC off for a while and you're good to go again. Noticed there is a good size puddle of evap water under both cars after a couple hours on the road. We're in the dog days of summer with high humidity (NC) so I'm wasn't surprised to see icing of the evaporator so I hadn't checked pressures yet.

Got to thinking that both cars should have evap temp sensors? It's a low motivation Sunday today and it's hot and humid so, I did a quick internet search (instead of dragging out the gauge set) and it seems yup, they do have evap temp sensors. In the course of that search saw something about the Honda evap sensor output over time not matching the factory graph for temp and output in ohms. Evidently the sensors are a pain to reach so some have been measuring output and adding an inline resistor so the computer will shut off the compressor before the evaporator freezes. Is this a common Honda problem and common fix if the pressures are in line?
Al9
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Re: 2004 Accord and 2011 Civic, evap freezing on both

Post by Al9 »

Might be a good time to get the refrigerant charge recovered and its weight assessed and restored to factory specs, both cars.

Should evaporator pressure drop down too much due to a serious lack of refrigerant or a TXV "too closed" malfunction, the evap coil begins getting starved (let's put it this way in order to avoid using the F word of MVAC, that is superheat) and it progressively freezes from the inlet to the outlet (that little amount of liquid making its way inside boils at an abnormally low pressure and hence temperature) as the system operates. No LP switch on auto TXV based AC, so the fixed displacement comp keeps pumping (whereas a variable displacement comp would destroke due to the control valve detecting an abnormally low suction pressure) and things stay apparently cold as long as the TXV isn't basically receiving 100% vapour instead of at least some liquid.

The evap temp sensor is meant to control the temp of a uniformly cold evaporator, and it's meant to do so by detecting air temperature. Air stops flowing through evap fins due to a nice ice layer, no way to know how cold the evaporator actually is. The TXV is calibrated so that it progressively floods the evaporator as it gets cold in order to keep the evaporator pressure high enough across the entire coil and prevent any coil icing, but a lack of refrigerant prevents this flood from taking place.

Not to mention that, due to the starved evaporator, the compressor is running hotter and receving less oil than it's supposed to (a few droplets of liquid refrigerant making their way to the comp carry way more oil than 100% vapour refrigerant), so it's wearing down at a faster rate.
DetroitAC
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Re: 2004 Accord and 2011 Civic, evap freezing on both

Post by DetroitAC »

ScottNC,
If these were my Hondas, I would first get the refrigerant charge correct. The evap thermistor is placed in an experimentally determined spot downstream or shoved in the fins of the evaporator. There is almost never a "perfect, optimum spot" so those Honda guys might have been chosen a spot that is not great, but kinda works, can be assembled, wiring can sort of fit, but the core is going to freeze at low charge. At a correct charge the thermistor might be in a properly refrigerant fed location of the evap, but at low charge it might be in a starved/superheated area of the evap.

It's counter-intuitive I know, but low charge can lead to freeze-ups for this reason. Residential A/C guys know that very well, happens all the time in those things.

It might also be a thermistor with resistance that has changed as you suggest, your logic is also sound there. But R-134a WILL ALWAYS LEAK OUT over time, both of those cars are probably due for a recharge.

When the A/C is working well, are all of the vents the same nice, cold temperature, or are 1 or 2 of them warmer?
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JohnHere
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Re: 2004 Accord and 2011 Civic, evap freezing on both

Post by JohnHere »

DetroitAC wrote: Mon Aug 23, 2021 8:23 am If these were my Hondas, I would first get the refrigerant charge correct.
Absolutely agree.
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Cusser
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Re: 2004 Accord and 2011 Civic, evap freezing on both

Post by Cusser »

I'd also make sure the condensate drain line was clean/open.
ScottNC
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Re: 2004 Accord and 2011 Civic, evap freezing on both

Post by ScottNC »

Thanks for the replies. Having in the past experienced a low charge causing evap freeze-up on household AC I should have realized what was up. Have been waiting for a late-in-the-day slot to open in the schedule of a friends auto repair shop. He has the equipment to discharge and measure the existing refrigerant. All I have is a vacuum pump, gauge set and misc. AC specific tools.
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JohnHere
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Re: 2004 Accord and 2011 Civic, evap freezing on both

Post by JohnHere »

Very good. Be sure to let us know the outcome.
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