2010 Honda Fit Sport.

Symptoms:
On two long trips I've had my A/C really start struggling to produce cold air. It really starts limping along. On one of the trips some small pieces of ice came out of the passenger side air vent. Also, on some mornings on my way to work when it isn't that hot out yet but I want to run the A/C to cut the humidity I've found the air it blows was very cold, to the point where it was blowing fog-like air out of the vent.

Not sure if this is related or not but when I idle at red lights my A/C doesn't seem to be very effective. Not sure if that's because there's no air moving into the system or if that's just how it works. It seems like other bigger vehicles don't have this last "issue".

I've been reading around FitFreak and have seen a few threads with some similar issues but none that seemed to exactly match mine. Curious if anyone has any ideas for me or threads I can read.

Thanks for your help. I'm not a car guy and I'm not very mechanically inclined. This forum has been extremely helpful whenever I've had questions.

 

Mine also doesnt work at idle, stuck in traffic, etc. About your freeze issue. Any idea about your cabin air filter and if its really old and clogged?

 

Core freezes solid because the system won't cycle the compressor off ....(or cycles at too low temp)

Assuming the compressor clutch relay isn't stuck on (another fairly common issue on some of the cars)

I've had to replace the evaporator temperature sensor for this issue.

 

Reading various posts here I hit upon this topic as well. I haven't checked it but I will. It's been a few years since I can remember changing it myself and I'm not sure if the oil change folks have actually changed it. Will need to confirm tonight. A solid point to check on - thanks!

I'm going to guess it's more than just bad air flow from what I've been reading but its always possible.

Does anyone know if the A/C acting a little funky will have any impact on the defrost? If I just leave the issue alone until next Spring/Summer is there a chance it could do more damage? I don't know how the systems may be linked, if at all.

 

Job #1 of an air conditioning system is to dehumidify the air. It has to remove moisture from the air before it can cool it efficiently.

The AC is automatically turned on when the system is set to defog position.

If the AC does not work at all then you may have to deal with fog/moisture on the inside of the glass longer than if it worked correctly.

If it cools to too low of a temperature you may see ice cubes being spit at the glass or frost forming on the glass, unless you crank the heat up
But even with the heater temp up, the AC evaporator core can still freeze up if the system is running, in the condition it is in.


The HVAC system is supposed to cycle the compressor off before the evaporator core temp reaches freezing. Most seem to cycle in the high 30s to low 40s (*F).

 

The rest of your post is reasonable, but this makes little sense. The air conditioner dehumidifies the air by cooling it below the dew point, the same as (most) household dehumidifiers. Sometimes you, as the driver, may care more about the dehumidification than the cooling, and sometimes vice-versa, but physics dictate that it can't help but do both when the incoming air is warm and moist.

The only other way to dehumidify air is to use some sort of a hydroscopic chemical that absorbs the water directly and needs to either be replaced or heated from time to time to get rid of the absorbed water. I guess if you're talking about relative humidity you can also "dehumidify" the air simply by heating it, but that of course doesn't change the absolute amount of water vapor in the air.

 

Not an engineer, not a rocket scientist........ That phrase "Job #1 of an air conditioning system is to dehumidify the air" is part of what was taught to me.



An automotive evaporator core might be only 3 inches thick, there's a lot that has to happen in the very short time a given quantity of air spends passing through it.

Considering AC system cooling efficiency and its ability to remove heat, air temperature drop as it moves through the evap core in a single pass will usually be less with very humid air than if the air is very dry, given identical air temps prior to passing through the core.

WHen passing through an evaporator core, air @ 70% humidity might only drop temperature by (example) 15 degrees F, whereas air at 15% humidity might drop 20 or more degrees in a single pass even though the evaporator cores surface temp is the same.

AC system performance evaluations normally take into account relative humidity because it has a large influence on system pressures vs. expected and acceptable temperature ranges.

 

I realize this might actually be an idiotic question but does the defrost setting do anything other than point hot air at the window? Is there anything else that's happening?

For some reason I always thought it was some sort of magical heating option but maybe it's just not that complicated.

I've probably answered my own question.

 

You are entirely correct. As you cool the air passing through the evaporator the air's ability to hold moisture is reduced and the excess moisture is extracted or condensed on the evaporator fins. The collected moisture drips down the evaporator core where it is collected and routed or piped out of the car.

The problem when the evaporator runs too cold, the condensed moisture freezes on the evaporator reducing it ability to do any further heat exchange to new air trying to pass through it.

Running too cool can be caused by many things, but the primary cause is the system is undercharged with refrigerant. The lower temperature limit is set by the pressure at which the refrigerant evaporates. Lower system pressure means a lower evaporating temperature point.

Go to Walmart in the housewares section and buy a digital cooling thermometer for $10.00. Stick it in the center vent and watch the air temperature as you drive. If the temperature ever goes below 40F then the system is undercharged. Usually the lower limit is around 44F to 46 F. I have my lower limit set to evaporate at no lower than 39.5F. I would not go any lower than that.

 

I have a digital meat thermometer. Would that work? I just tested it in my freezer and it went down to 5° F...I don't see why not.

Edit: this is what I have

 

AC runs automatically when front windshield defrost (defog) position is selected (most cars).
You control the temperature.

Disagree.
Your explanation will certainly hold true in a stationary or central air conditioning system where there is no direct monitoring of the core temperature and no compressor controls directly related to the evaporator core temperature, but on this car the compressor is designed to be cycled off and on to control minimum AC system temperature based on direct monitoring of the core temp.

Refrigerant undercharge in a MVAC system normally results in elevated vent temps.



Compressor is cycled OFF before the evap core reaches freezing temp, then back on at roughly 5 degrees above shutoff temp.. Repeat.

Core temp may reach mid 30s, vent temps are usually just a few degrees higher than core temp.

The very small AC systems in some of the Fit and newer Civic and other small cars seem to be set to cycle at slightly higher temps, probably intended as a slight fuel economy boost.
On Accord, Pilot, Odyssey I expect to see vent temps drop below 40 rather quickly.


OP already has ice being spit out of the vent of his Fit, it's pretty obvious what the temp at the vents and temp in the core is going to be. Too dang cold, but not because of undercharge.


I think the OP needs a new evaporator temp sensor in his Fit.

 

I have like 4 digital thermometers from Walmarts kitchen section, maybe cost 10 bucks each and all read within a degree or so of each other.

 

That is exactly what I use. They work great because the sensor is actually stuffed down inside the vent. The temperature read there is not exactly the same as the surface of the evaporator. It is within a couple of degrees of the actual evap temp and is easily accessible there.

I primarily work on Automotive AC systems. I have done 3 or 4 building type AC systems over the years. Buildings are simple when compared to automotive ones.

Automotive systems vary slightly in design and method of control. Some systems, especially with an expansion valve instead of a orfice tube, have an evap temperature sensor. These days the primary way that low temp cutoff is done is by sensing the low side and high side pressures. This is also what normally cycles the clutch and not the temp sensor on the evaporator if it has one.

In the end they all operate similarly and if they are freezing up, simply add a little refrigerant then the evap expansion temp can not go below freezing.

 

This car (and most other Hondas) is not controlled that way. Compressor clutch cycling is regulated by evap core temperature sensor, not system pressures. Hondas do use a TXV, not a fixed orifice.

The high side pressure sensor data (on newer cars) is fed to the PCM to control high and low pressure safety shutoff points, and to control the radiator fan(s) off/low/high speeds (depending on the vehicle and system).


This system won't freeze up the evaporator if it is low on freon. Adding more might make it stop freezing if you add enough, but not for the reason you give here. It would be because of an overcharge condition, if anything, and that's hard on the system.

These systems are so small and have such little reserve capacity that just a couple ounces over or under charge weight target can result in decreased efficiency and elevated vent temps. Just a little more charge added can make the high side hit the cutoff pressure limit (around 500 PSI IIRC) and bog the engine as it tries to cycle against super high head pressure.

HTH

 

If the vent airflow slows and you get ice from the vents, check the charge. When the charge starts to get a little low, this happens. I have two fits, adding a few oz's of refrigerant always fixes the problem.

 

My 2012 fit, since day one, would go about 1+ hours before the airflow volume out of the vents decreased and the A/C became useless. Turn off the A/C for 10 minutes and let the vent flow on recirc defrost the evaporator, and I was good to go for another 45 mins to an hour. Took it to the dealer in 2014 while in warrantee and got the "everything is normal and within spec, we even let it idle for 1.5 hours no problem". Had to drive a long distance (NH to Tenn and back) in summer of 2015 with my wife and sister in law and the problem really bugged them - they had a lot less patience than I had. Went back to the dealer again in 2015 at about 45K miles and explained politely the problem, how it still wasn't fixed from last year, and how it just wasn't right. Service manager was very polite and helpful. Next day it was fixed. They drained the system, checked for leaks, pumped it down twice, and refilled with the correct amount of refridgerant. Service manager admitted that refridgerant was very low, but there were no leaks in the system. 1 year later at end of 2016, no issues. The cynic in me wonders if Honda did a cost-benefit analysis and determined that for some cars above a certain latitude they could get away with a lower amount of refridgerant. I am happy it runs like a normal A/C system now.

 

The amount of refrigerant saved between the low and normal level is insignificant. I haven't had to buy a 30 pound bottle recently but, going rate right now iis a little over $2.00. They spend more in labor than the minor amount of R-134 saved is worth.

I think the real problem is inattention to detail when initially charging the AC at the factory. The second problem is lack of AC diagnostic skills at the dealer. They only know how to set the recharge machine and then stand back and watch. If the AC does not work properly when they are done all they say is nothing is wrong with it. Your's was a simple problem to diagnose using a thermometer and a set of gauges but the average AC today has no clue how to use those simple tools today.

I had a related problem on a GM vehicle. They recharged it twice with a machine to no avail. I finally got out my gauges and found it overcharged. I bled off a slight amount and got it back to normal operating ranges. My time spent was 15 minutes. Time spent on two previous trips to the dealer - 4 to 5 hours. Sometimes is pays to fix it yourself even under warranty.

 

Yup, I agree. The problem with my GE8 just re-inforced that sometimes the dealer doesn't really dig into the problem. It is more cost effective for them to follow "standard work" which is "hook it up to computer and the AC recharge machine and we will figure out which subassembly to replace". It is even worse in my home state of New Hampshire: in the words of the service manager: we only get A/C problems for about 3 months out of the year. Not much experience = not such an expert with the system. Since I was going back for a repeat problem I was hoping Honda would honor the warrantee, even though I was out of miles. They did and I was happy.


I also had a 2004 Civic this year with inoperative A/C. My attitude was going to be "it's used, it's broken, it's an older car, A/C will never work again". But I couldn't give up. I already had a factory manual. I found the mag clutch problem (air gap too big) and fixed that, and then found the A/C blew only kinda cool. Well, actually not cool at all.


Went to HarborF, bought the gages, bought the temp probes for intake and vent air, wrote down all the pressures and temps, compared it to the pressure and temp curves in the manual, and figured pressures were low but no massive leaks and I was into it deep enough to take the gamble on 1 can of R-134. Charged it into the working pressure window. A/C is cool again. Dye in the system now. We will see what next summer brings.


It is not rocket science, and there is so much info even in the factory manual that with a little time, some tools, and some personal protective gear and a healthy respect for what you are working with, one can tackle some basic A/C issues.

 

If it is low again next year. The cheapest place to get single cans of R-134 is Walmart. Right now I believe it is around $4.88. So for $5.00 per year it is not worth the bother to find and fix the leak. Even if it took 2 cans per year, I would just add it and not bother to find and fix the leak.