By on August 11, 2014

Intercooler. Shutterstock user BACHTUB DMITRII

TTAC commentator Land Ark writes:


I recently acquired a 2007 Honda Civic EX sedan from a neighbor who moved out of the country. I got a really good deal on it and for the most part it’s in good shape. It has 80k miles, 5 speed, and one major flaw. The air conditioning is a little bi-polar; sometimes if blows cold and sometimes not.

It always feels cool to cold coming out of the vents but it doesn’t cool the cabin down. It seems to get warm most consistently while sitting still, like at a red light. My first thought was that there wasn’t enough R gas and I would just trundle down to my local big box retailer and pick up some Cold in a Can. But my thinking was that 2007 is too new for it to be out of gas, could it be leaking? I determined that was not too likely since the air coming out was still cold and because the temperature fluctuates and I would think a leak would cause the temperature to remain constant as the gas leaks out until there is no cold air blowing at all. I definitely could be wrong on that though, I’ve never had an A/C go bad on me before.


  • AC is cool but not cold.
  • At red lights the inside of the cars gets noticeably warmer. On the highway it gets noticeably cooler most of the time and warmer on occasion.
  • At idle the temp just outside the vents ranges from 68 – 72
  • If I get the RPMs up to 2500 the temp just outside the vents will drop to 65.
  • Clutch on the AC audibly engages when turning it on
  • AC cycles on and off as I would expect. The vent temp rises about 5 degrees before kicking back on.
  • The fuses are good.
  • I swapped the relays and noticed no change in behavior. I left the compressor relay out and it stopped functioning as I would expect.
  • The clutch spins when the AC is turned on and does not spin when it turns off.
  • Both fans spin when the AC is turned on.
  • I ran the self diagnostic check and the recirc light did not blink.
  • I measured the pressure with both front doors open at ~80 degrees and got 40 low and 160 high.

I took to the Civic forums and it appears it is a wildly common problem with this and the previous generation. There doesn’t appear to be one common cause or solution. Lots of people trying things and having that fix it only to post a few days later that it stopped working again. I have checked and both electric fans are functioning, I can’t say that they spin all the time but when I checked both were working. So that is the only symptom I have ruled out. I read that sometimes something in the compressor can break off and block the lines. My fear of trying to add some R-134 would be that most cans come with leak sealer and if there is a blockage and no leak I wouldn’t want to send sealer through the system.

The most likely candidate for the problem seems to be the compressor clutch. I don’t know why I think that other than it was mentioned and seems like it would be impossible to fix in your driveway so no one has tried to replace it and reported back that it didn’t work.

I haven’t dug too deeply into the car but I bought it to get used to driving a stick and it spends lots of time sitting when it’s hot out so I am missing some good opportunities to drive. And because I plan on selling this car in a few months, I am not interested in putting a whole new A/C system in it. So what should I be checking/testing? I’ll try anything that doesn’t require releasing the pressure on the system, otherwise I’ll have to take it in.

Sajeev answers:

I’ve personally experienced poor air conditioning in a co-worker’s Civic on a wonderfully hot and humid Houston afternoon. And when A/C systems don’t work but pass your (comprehensive) diagnosis, thank goodness for forums that agree with us. In particular, commentator Rayspitcher41:

“Went and had my A/C recharged and a dye test done for $50. Turns out my compressor was starting to go and so was my condenser. It cost about $650 to repair with labor, but my extended warranty covered it all so I had no out of pocket. I have a 07 with 60K on it. Now the A/C is running Ice Cold within a mile of starting and driving and I’m in south florida with a heat index of 103 every day.”

In theory, air conditioners operate below peak efficiency when the engine is idling (below 1000-ish rpm) because the compressor isn’t effective at those speeds.  But that’s Problem #1 in this two-pronged quandary. I suspect one of the HVAC’s radiator lookin-thingies is also to blame: the condenser or evaporator.

I suspect the condenser. Look at which HVAC component takes the most abuse: the condenser is a big net that catches anything in front of the vehicle. (The evaporator safely nests inside the dash.)  Assuming that every 8th Gen Civic owner is happy with the HVAC when new, odds are the condenser loses efficiency over time.  Combine that with a compressor’s ineffectiveness at idle and you have a hot mess of a problem.

So what do I suggest? In this order:

1. Check the pressures you find against a Honda service manual, add or remove refrigerant safely (don’t vent to the atmosphere, obviously).

2. Keep the idle above 1000 rpm when you need cold air.

3. Clean the condenser “fins” and inspect for physical blockage.  Use a condenser fin comb (yes, really) to fix bent fins.

4. Replace condenser, look for an upgrade from a revised design or newer model.

5. Replace compressor.

6. Give up and sell it.

[Image: Shutterstock user BACHTUB DMITRII]

Send your queries to [email protected]com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

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37 Comments on “Piston Slap: Condensing Honda’s Hot Air?...”

  • avatar

    Replace the pollen filter if it has one, luxury cars mostly have had them since the 90s but they are also on mainstream cars nowadays. You need way more air volume to cool than to heat , a blocked filter can really mess things up.

    The filters are supposed to be replaced every year, but rarely are. They are usually somewhere around the heater core inlet. They do become very dirty.

    • 0 avatar

      +1 good point.

    • 0 avatar

      The cabin air filter on a Civic (or an Accord as a matter of fact) takes about 3 minutes to change. It sits behind a small door behind the glove compartment.

      -Empty the glove box.
      -Unhook it at the top, you should see a small door.
      -pinch the clips, pull on the filter, replace with the new and reassemble.
      -It’s that simple! (Not like in my wife’s Mazda 5)

  • avatar

    I have a 2009 TSX with the 2.4 and six speed since new. It’s black to boot. It’s common. While a big v8 has big compressor and balls to run it at idle on a 4,its much more of a drain. Their compressors are smaller. That combined with no air coming into the car at idle for air and cooling the car has to shut down the air conditioning somewhat to lower the motor load and keep the engine cool. Get back up to speed, cooling improves and the compressor comes back on full. Mine doesn’t send as cool air at idle but it’s normal. Top up your refrigerant but I don’t think there is anything to fix.

    • 0 avatar

      Incorrect: the 74hp Mirage I road tested had twice the HVAC balls of your average 8th gen Civic in bumper-to-bumper traffic on I-10. And it’s five door blueprint gets a lot of sunlight.

      No excuses if Mitsubishi can do it!

      • 0 avatar
        Land Ark

        I’ve had a number of 4 bangers over the years starting with a 1986 Sentra and then a long time in a 1990 Sunbird up to today with my Legacy GT and all have ice cold AC all the time. I also had a 2000 Civic that had fine AC, which is what caused the initial concern. Had that one had the same symptoms I’d have written it off as an “all Hondas have bad AC” issue.
        I will say that I had a Scion tC that was on the weak side from new, but it wasn’t as bad as this car is.

      • 0 avatar

        I don’t doubt it. That’s why Honda and Acura go 300,000k and Mitsubishi doesn’t. Honda keeps the motor cool and doesn’t boil the nice protecting properties out of the oil at idle, Mitsubishi keeps right on running the motor and compressor at the same speed. You realize there are actually engineering reasons like this that make Hondas so reliable, right?

        In the 70s and 80s GM used to run its low HP engines so hard running compressors at slow driving speeds in the summer that if you shut the car off, the stored motor heat would dig the rings into the piston walls making the car impossible to start for 40 minutes or so.

        There are many subleties to making a small motor dependable, reliable and powerful. And to run in stifling weather for hours and days on end..

      • 0 avatar

        Note that the old ACs with R22 had a lot better cooling power than today’s with the R134a!

    • 0 avatar
      Don Mynack

      Most small cars have terrible a/c at idle, mostly because they have small compressors coupled with a dinky little fan pulling air across the condenser. Upgrade that fan to a double fan and you’ll see your car cool off much nicer at idle.

  • avatar

    Sounds like he’s not alone… I did a quick google for “2007 civic ac warm at idle” and got a number of hits from various forums. I’m not in a position to read them in depth, but that’s a good start to see if there’s a remedy.

  • avatar

    I just went through a similar situation with my mom’s ’06 Civic. The high side pressure varies based on ambient temp. Should be around 160 PSI at 80 degrees ambient.

    Her’s was a bit low. I couldn’t find any leaks evac’d/recharged with dye. The capacity of these systems are less than 1 lb of refrig, so even if they’re just a little low, their efficiency drops way off.

    I also found the air gap on the compressor clutch was a bit wide, so I pulled off the clutch plate and removed a shim to get it down to the min spec of .35mm (as I recall). Pretty simple to do in the car.

    The other issue with these cars (and unlike most Honda’s) is they don’t have a heater valve, they have constant coolant flow through the heater core, and shut off airflow through the core by closing a door in the heater box. So there is always radiant heat in the box, which likely reduces the A/C efficiency somewhat.

    …and finally, as mentioned above, a dirty restricted A/C filter reduces airflow through the system and hurts efficiency.

    I got my mom’s car to cycle between about 42-50 degrees at 90 degrees ambient. That’s the best I could do. Usually I can get Hondas to cool 2-4 degrees cooler, so I think it’s just a function of the design. It seemed to work better until the car warmed up, which makes me think the heat from the heater core is the real issue.

    • 0 avatar
      Land Ark

      Thanks for this. I’ve seen the shim removal suggestion but I’m hesitant because my measuring skills are sub-par (seriously, I can measure a yard stick with a tape measure and get 50 inches) and that seems like it would need to be spot on to prevent it from damaging itself.
      I changed the cabin air filter right after buying it, it definitely needed it, but I am not seeing a difference in temperature.
      I drove it over the weekend and had to turn the fan down as it got too cold inside while driving on the highway. Of course, it was cloudy and in the low 80s.

  • avatar

    If you end up doing any AC service where you open the system make sure you replace the dyrer/filter, accumulator, and the orafice-tube/expansion valve. Not replacing these items when you open up the system, in my experience, is inviting another failure.

    • 0 avatar

      I can’t speak for other makes, but I’ve worked on Honda’s for over 20 years. Unless the system’s been “open” for an extended period of time, or has debris in it from the compressor failing internally, I don’t see any reason to replace the dryer/expansion valve etc. Just a good 15min vacuum evacuation is all you need.

  • avatar

    I have a 2013 Civic, and luckily I don’t have any AC problems yet. But the one thing I noticed about my car (should be similar to the 2007 in question) is that the angle of the windshield and the length of the dashboard traps the heat and gets hot quite quickly in the sun.

    That plus when idling where it has been said AC is not at full efficiency, even with perfectly good AC, it gets quite warm in the car in stop and go traffic. My dashboard is black, and I’m trying to get a lighter colored dash mat to see if that can reduce the heat absorption.

    I’m thinking this isn’t a Civic specific problem, maybe any other car with a sloping windshield and dark colored dash would be the same.

  • avatar

    This is a good Piston Slap.

  • avatar

    Stupid Question

    Is the radiator fan running?

    No running fan while stopped or in slow traffic will lower the cold air output significantly. Gotta geek air moving over that condenser.

  • avatar

    If the vent temp is becoming noticeably warmer at stop lights to the point where it’s 72 degrees at the vents, I think that points to a problem. I would start with looking at the refrigerant level, even a small amount off can create an issue with such a small system.

    Doing things like getting “coil cleaner” at the hardware store and cleaning the condenser helps, but I think it’s probably low on refrigerant. You could just have a really small, slow leak.

    But some car companies just don’t put a priority on on their AC systems, and Honda probably has the most notorious reputation for poor AC. I owned a Civic years ago and it wasn’t really ac, it was just a system that kept you from sweating too much.

    I live in AZ, so a car has to have a strong AC and it’s just going to be a miserable vehicle to own.

    You can do some other things to modify, I’ve found it helps to get foam pipe insulation at the hardware store and wrap the “cold” ac lines (low side). The heat under the hood really warms them up. It only cost a few dollars and takes a few minutes.

    • 0 avatar

      It’s definitely low refrigerant. Get it recharged at a place that will vacuum it down and inject some die. In a week or two you should be able to spot leaks with a black light.

  • avatar

    The A/C (and with it, the defroster), mostly gave up the ghost on my ’08 Si last year at 120K miles. I tried recharging it, but that wasn’t the problem. It would blow cool, dehumidified air for a little bit after first starting it in cool weather, then the AC clutch would kick out, and that would be that: Steamy windows on rainy days, open windows on sunny ones. The dealer mechanic told me the magnetic part of the clutch that engages the compressor and all of the A/C goodies was not working, and that I had to replace the whole thing if I wanted to do it right. For $1,000 I’ll live with some discomfort since I love the rest of the car so much and I have to replace the tires soon at $175 a doughnut. Honda has a great rep for reliability, but on some recurring issues (steering racks, A/C units, Odyssey trannies) they don’t seem to be in a hurry to fix them.

    • 0 avatar
      DC Bruce

      I think an a/c compressor clutch failure at 120k miles is not much to complain about. I’ve experienced that problem on several non-Honda cars with much less mileage. The problem is the amount of heat they are exposed to, being stuck in a hot engine compartment.

  • avatar

    ‘Hilariously’ relevant for me. The AC compressor in my CRV just stopped blowing cold air last week, while on vacation. I was hoping i could have it looked at when I got home, but on the way home yesterday the compressor clutch started smoking violently, with the familiar smell of molten metal.
    So I had to have a towtruck pick the car up and take it to the nearest garage (80 miles from home), get a rental to drive me and my family home, and have a friend help me take my caravan home(and give back the rental) Luckily my insurance covers the towing and part of the trip home, but a new compressor (not a Honda original part,that would drive the cost sky high) will cost more than $2K including work…
    And this is a common problem with CRV’s all around the world, Honda even partly acknowledges the problem and have extended the warranty on certain parts, like the clutch, and have in some cases paid for the replacement of the whole AC system, since it often becomes contaminated with pieces of the compressor. (I believe my car is sadly gone beyond the extended warranty anyway, but I haven’t talked to Honda about it yet)

    • 0 avatar

      @Zyko – I have been reading about the same issues with my CRV. Apparently the Japanese built ones are more prone to it, mine is built in England so might not have the grenading compressor. I have been having some strange issues with mine… if the car idles for a while the AC will stop blowing cold, driving it again fixes the problem. But my car also has almost 230k miles and the AC is all original so I am not sure I am going to spend big money to fix it if it gives up the ghost.

      I always think of Hondas as legendarily reliable, but I can admit they have some random weak spots like this and the V6 auto trans issues.

      • 0 avatar

        Mine is built in England too ;)
        As far as I know the problem covers all CRV’s from 2002 through 2010 (so far) but there seems to be a certain link between usage/climate and when the issues occur. I live on the west coast of Norway with a humid varyig climate, and my car is mostly driven short distances on weekdays (and it seems both previous owners did the same,as it only has about 60K miles on it, but was registered in February 2007) meaning the compressor has to turn on and off more often.
        Your issue may just be that the cluth for the compressor engages and disengages when it ‘feels like it’ to save both the AC system, and the reduce power robbed from the engine. If it has lasted that long it may just last the rest of you cars usable lifetime.
        PS: I think Hondas legendary reliability may be somewhat of a problem for Honda, because there seems to be an outrage everytime there is something wrong with one, and both dealers and customer service people seem to have a hard time believeing they can fail :P

        • 0 avatar

          My CRV has spent most of its life driving longer distances so that might explain why I’ve been lucky. But the idling issue has only started this summer, it didn’t have a problem before, so it could be a sign of bigger problems. But as you said, it may just last the useful life of the car so I am not looking to spend big money fixing it now. I just don’t park and idle that car with the AC on anymore.

          Excellent point on the legendary reliability, I have seen that affect my ability to have problems diagnosed. If my car was newer or lower mileage it would bother me more, but as it is I am a cheapskate and usually diagnose and fix things on it myself.

          • 0 avatar

            I fear the compressor clutch on your CRV may have started singing it’s last tune. And I guess it’s driven by the alternator serpentine belt, which can be taken out if the clutch gets as hot as mine did when it failed. If its possible to have just the clutch looked at and replaced, that may be cheaper in the long run than just letting it run until it fails. I probably would have fixed my own car if I had made it all the way home before it failed, I hate paying strangers to fix my cars too ;)

          • 0 avatar

            Good advice, I might go ahead and proactively replace that.

      • 0 avatar

        That most likely is a bad clutch or maybe just low on refrigerant.

  • avatar

    1) Slap a gauge on the low pressure side. It sounds like you have too much refrigerant in the system. It freezes up and then thaws, causing the cycling between cold and cool.

    2) The next best idea is hook up a vacuum pump with gauges on the high and low sides, empty it all out, and then put in no more than the recommended amount of refrigerant.

    If this car ever had a dealer or national chain AC service the first is very common.

  • avatar

    Skip the DIY a/c service and have it serviced properly.

  • avatar

    Visit a professional and have them properly charge the system and while they are at it replace the valve cores in the service ports. Hondas are know for leaky valves and with the small amount of refrigerant it needs to be spot on for proper cooling. Do not mess with trying to charge it yourself there is no way to get it properly charged w/o recovering what is in there and recharging with the proper amount. The poor at idle is a symptom of the low charge. Once you get up to speed there is enough air flow for the condenser to supply liquid to the evaporator.

  • avatar

    I live in Florida, we have been having the hottest summer I can remember this year, and me and my family have a bunch of Hondas of varying ages. Two 2013 Civics, a 2003 Civic, a 2002 CRV, plus my 2008 GTI, 2001 MR2, and my brother in law has a 2003 Dodge minivan. Everything except the Dodge has a black interior.

    All of the Hondas have stellar AC, cools the cabin off quickly, even after sitting in the sun all day, maintains temperature to the point where we almost always have to move the temp dial slightly off full “blue” to not have such cold air pumping in. My CRV as I commented above has an issue if I leave it sitting idling for a while, but that is a new problem, never happened before and we do that quite often for a random reason I dont want to try to explain right now. The MR2 AC is phenomenal, even with the thin convertible top, but I suspect that is more because its compressor is sized for a Corolla sedan and not a tiny 2-seater with half the cabin volume. The VW was the worst of my cars, it would take 15-20 mins to get the interior cool on a really hot day, you could just feel the heat emanating from the dash sometimes. But the heat was amazing, actually too hot to use even in winter in Florida and hard to regulate for slightly cooler temperatures. Clearly the Germans value heat over AC! The Dodge has terrible AC, but that thing is all windows and has no tint so its to be expected. Most of my cars have tint which helps, but not as big a difference as you would think. The MR2 and 2002 Civic are not tinted, the newer Civics and GTI have full tint, the CRV has factory tint only.

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