Climate Control

General Climate Control Issues

Many dealers are not very good at diagnosing climate control problems well, the A/C system in particular. A "shotgun parts replacement" technique, where they just state that the required fix is to replace anything they think might be part of the problem, will usually indeed fix it but at far greater cost than determining the actual problem and replacing only what actually needs to be replaced. This can be a difference of thousands of dollars so it pays to make sure you understand exactly what is going on.

How cold should the A/C be?

[GM – 2001/7/9] The vent temp spec for the NSX’s Freon-based air conditioning system is 45F at 80F ambient. If your system won’t blow below that value you probably need refrigerant. Check the sight glass for confirmation. My 91 blew 33F when new and blows 36F at eleven years old. The system has never been recharged.

A/C is cold one one side, warm on the other?

This is a common problem and is usually due to a low refrigerant level ("freon") in the system. Of course the reason there is a low refrigerant level is because there is a leak somewhere. It may be a big leak or a small, slow leak. There are also several possible places for the leak to occur. It may be something simple and cheap to repair like a failed O-ring or it may be more complicated and expensive like a hole in your evaporator.

[BDE – 2001/7/8] If both of your condenser fans are operating normally, the only other thing it could be is a stuck expansion valve. I’d take it and have someone look at the high and low side pressures to see if they look alright for the vent temp your having. If your low side pressure is close to zero or lower (in a vacuum), and the high side is above 170 or so, more than likely you have a stuck expansion valve. Of course the freon level needs to be as close to full as possible to get an accurate diagnosis.

[MBA – 2001/7/8] An NSX, like a Vigor, is one of those cars that when the freon gets low, you get cold air at one vent and not at the other. You can verify this by looking at the sight glass which shows the level of freon. The sight glass is on top of the receiver drier, which is an aluminum cylinder mounted right in the middle in front of the radiator. Look at the glass with the engine running and the a/c on. If the glass is totally clear, freon is full. If you see a trace of bubbles, its a little low. If the bubbles are more like foam, you’re at least a pound low. The key question here is how long did it take to loose the pound, or half pound or whatever it is missing. If it has not had freon added in a while, we have no way of knowing if this is a fast leak, or a slow leak. Either way, as Lud points out, fluorescent dye is clearly the leak detection method of choice. It needs an a/c charging set up, same as is used for installing freon, to add dye. Once the dye is added, you wait till you have lost a few ounces of freon, as determined by checking the sight glass daily (takes about 20 seconds to do). The reason you want to do it often is to catch the leak as soon as possible. The sooner you catch the leak, the less 40.00 / lb freon you will have lost.

Once the freon level has diminished, its time to discover where. This is done by illuminating all possible components with a black light. This is where the NSX skill comes in. (any a/c shop can install the freon and dye) There are more places to loose freon in an NSX, than any other car. Between the front / rear split of compressor and other components, dual condensers, etc., there are dozens of potential leaks. Don’t forget to remove the tunnel cover under the car, there are two lines and six fittings in there. You will have to remove the black plastic vents in the front bumper to properly see the entire condenser (s). If no leaks are visible anywhere, the last place to check is the (dreaded) evaporator. You can pull the blower motor and see most of the evaporator thru that hole, which only takes about 20 minutes, as opposed to 6 hours to replace it.

Can I Update My R12 System To R134A?

[HS, A/H] Acura has come out with a update kit to change the R12 to R134A. The bulletin is very specific: The existing A/C system must be in good working order (no leaks). This update will not cure an existing leak in the system

I had this update done on one 1991 NSX several weeks ago and the driver states that the A/C seems the same if not a little colder.

The Acura part number for the upgrade kit is 38020-SM4-A1AH. Parts: $63.76 plus $43.20 worth of coolant.. Labor: $155.20.

R134A Alternatives

[MBA – 2000/9/16] I offer all my customers- NSX to Civic, the Freeze 12 option when doing a repair or recharge. I buy it in 30 lb cylinders for about 150. I sell it for 7.00 a pound, so its more like one fifth the price PLUS you only use 78 % Freeze 12 as the systems R12 capacity. It uses less because its compressibility is so much greater, that it expands into a slightly larger space. (not sure I explained THAT correctly!) I’ve used it in about 200 customer cars this summer, plus my NSX, and the fully custom built a/c in a conversion racer I’ve been building this summer as well. Not a single problem and the vent temps are 3 or 4 degrees cooler.

[MBA – 2001/7/2] 15 minutes is the standard amount of time used to evacuate an a/c system of air and other impurities. It only takes seconds to get the freon out- its the rest of the ‘stuff’ you are evacuating. However, sucking on the system for a bit longer, say and addl. 30 minutes, is common practice if a system has been open for a while or if you are converting but the advantage is minimal. In 15 minutes you get *probably* 98.5 per cent of the stuff out, in 30 minutes, 99.7 percent, so the extra time- say a total of 45 minutes, is doing "the extra mile" thing because if the system is / was *heavily* contaminated, that extra .5 percent could add up to something.

Compressor Failure

[DHA] The freon is mixed with oil. The oil acts as lube for the A/C system. This would include your compressor. So, if you are low on freon, this could explain the compressor failure. Low freon, low oil equals BAD!!!

On the other hand, Acura had a SB out on additional oil for A/C systems for 91’s as I recall.

Quiz your tech on the receiver dryer. This asks like a filter on the entire system. If your compressor is cooked (bad joke), very common that all kinds of metal particles are circulating in the system. Do not to delay in having this checked out ASAP.

The "black death" failure can cost well over $3000.00. I escaped for just under  $1400, thanks to lots of help by my local dealer, Superior Acura (Cincinnati). They (not Acura) goodwilled tons of labor.

[BDE – 2001/7/8] Usually on a healthy system, the low pressure side (depending on temp and humidity) will be around 30 to 34 psi. And the high side will run around 150 to 175. (These specs are for R12). (Also depends on the accuracy of the gauges your using). If your high side is way high, you probably have an expansion valve that is stuck closed, or possibly has a small particle of whatever in it. (Technical huh)!? This stops the flow of freon through the valve causing the pressure to build on the high side and causing the pressure on the low side to drop. A compressor will whine sometimes if the system is low of oil/freon, or is in a strain from trying to push freon through a restricted system. 

[MBA – 2001/7/8] The compressor itself is the same as a 91 to 92 Legend and a number of other late-model Hondas. The part that makes it an NSX compressor is the manifold which bolts on and can be swapped from your compressor to the new one. If you buy a rebuild, you will have to swap this manifold anyway. The Nippondenso part number is a 10PA17c. Be careful, the same number without the "A" is a 88 to 90 Legend and does NOT interchange. 

[MBA – 2000/10/6] ANY time a compressor seizes to the point that the belt smokes, you can bet there will be heavy metal contamination throughout the system. Most likely what failed is a piston, which is light alloy and when it seizes, it flakes small metal frags everywhere. The technician must do a major flush of the whole system before installing the new compressor. You remove the compressor and drier and the expansion valve. Then what you have left is the condensers and evaporator, plus the lines, which you clean using compressed air and a solvent commercially available just for this purpose. After the lines and parts are cleaned, you install new compressor, new drier, and new expansion valve. There is nothing in this system that cannot be flushed, same as in in any other car, though it is harder to do. Been there, done that, and it works just fine. Only hard bit is flushing the evap. You have to rig a hose to one fitting, and flush thru the other, so as not to make a mess spraying solvent under compressed air into the evap case. The solvents will melt the thermal lining in the evap, which is a thin layer of Styrofoam. (ever put gasoline in a Styrofoam cup?) Selling you everything new for 6k$ certainly guarantees they will get it right this time, but so does doing the job correctly, reusing the parts I recommended, and replacing the rest.

Evaporator Failure

[BDE – 2001/7/8] The fastest way to find a leak in an evaporator is to put dye in the refrigerant, then remove the blower from the front wall of the car and look at the expansion valve / evaporator with a UV light. That takes all of the guess work out of it. The one in the shop now had a charge done on it by me about 4 weeks ago. He NEVER drives this car. (91 18k miles). He took it to the warehouse that the car is stored in and parked it. Then 4 weeks later, pulled it out to drive it one nice day. The a/c wasn’t blowing cool at all. So he brought the car back in. I checked the evap drain tube with the UV light. Nothing was there. The rest of the system looked fine. So I pulled the blower and there it was! Dye was all over the evap. The car hadn’t been driven but only 44 miles. So the evap didn’t have time to leak the dye from the drain tube.

[MBA – 2001/4/11] The evaporator has been known to go bad on early cars, though I *think* all the ones (7) I have done were 91’s. It is possible however to have this part go bad on any car. If the only symptom you have so far is insufficient cooling, it could be a lot of other things. On the list of top ten repairs to the NSX a/c system, evaps are probably no more likely than 7 or 8. As for tips for the tech, hopefully he will know all he needs to, but one thing he may not if he’s not an NSXSpert, is the fact that you can check the evap for leaks without removing it, or even the dash. You can remove the blower motor housing, which takes about 10 minutes, and see the evap thru the opening in the body. You can’t see the whole evap, but you can see the part that ALWAYS leaks. The rest of the diagnosis is standard a/c stuff. The most common leaks are at the compressor. IMPORTANT- If the leak is the top seal (manifold o ring) on the compressor, Acura does not offer this part, they make you buy the whole compressor for that part. I have them in stock if you can’t find one at a local a/c shop. Its the same for about 50 different Nippondenso compressor’s. Yours, BTW, is a Nippondenso 10PA15c And, as to goodwill, I have not seen them buy one in about two years, BUT, if you’re the original owner AND have a good service history, its worth asking. For 1100. dollars, I suppose it’s ALWAYS worth asking.

[ – 2001/6/9] I replaced my evaporator myself. The evaporator was quoted at about $700, but I purchased it from Dave at Asian Auto for around $450 with misc. parts. It’s labor intensive (not the evaporator placement, but the entire dash and fan assembly removal; Next time I’m taking it in).

Vents Only Blow On High

There is a TSB on this issue for ’91 and early ’92 NSXs: [TSB_92-007]

In the failure described by the TSB, part of the blower motor becomes contaminated causing higher electrical current draw which in turn blows out the power transistor. The fix is to replace both those parts. Many owners have had this repair goodwilled by Acura.

Most issues with the blower only running on high are caused by a bad control unit.

Fan Speed Weirdness

[CA – 99/8/26] The problem was in the fan speed selector. The first few selection blew at only low speed, the middles few selections did not blow at all, and the top few selections blew at high speed, very strange. Acura had to get a special testing device and was able to troubleshoot it to the AC controls themselves. The new unit should be in by tomorrow. I am not sure if anyone else has had this issue besides myself. The good thing is the extra warranty is going to pay for this (over $1500.00 with labor).

Blown Fuses / Bad Cooling Fans (not vent fans)

Symptom: The AC works fine when the car is moving but not at low speeds or idle.

Page 22-52 of the ’91 service manual shows the troubleshooting and fuses to check for the consensor fans not running: No. 4 (15 A), No. 36 (10 A), No. 37 (10 A).

If the fan is physically stopped anytime it is turning, the fuses can blow. Anything from foreign objects to running  through a deep puddle which scoops water into the intakes in front of the tires can do it.

Regarding other comments about the car not cooling well when the car is stopped but working fine when moving: If that  is true, your condenser fans have a problem. The fuses above are the first thing to check. When it’s working right, the car will stay quite cool standing still at ambient temps well over 100 degrees F. The system was extensively tested in Death Valley.

Fun Fact: Part the reason OEM fog lights are not an option in the US, even though the car is wired for them and they’re available in Canada, is that in the warmer parts of the US they were found to restrict airflow a little much for the system to run at it’s best.

[JS] EXACTAMUNDO! I have had the same problem. The fuses are located under the front hood on the left, not the engine bay. I had two fuses blown! I live in Florida and stop lights have been a drag.

If your low side pressures are high also, you may have a cooling fan out on one of the condensers. But usually if that’s the deal, the pressures won’t be dramatically off. (2 times normal pressure).

[CTH – 2001/7/7] There are three fuses to check: Two under the hood (36 & 37) labeled compressor fan left and right (10A) and one master fuse for the whole climate control system located on the side of the driver foot well down near the clutch pedal (4, 15A).

But it’s easy to tell if you have a problem without even checking the fuses: with the car parked, turn on the A/C and go around to the front of the car. You should hear both fans quite clearly; you should also feel a distinct breeze going past each compressor (bottom outer holes in the nose).

Bad Odor From The Climate Control System?

Almost any car with air conditioning can, from time to time, have a musty or mildewy odor from the climate control system.  This is just what it smells like – mold growing in the vents, evaporator, or vent intake. Just about every car manufacturer (including Honda/Acura) makes a spray that is applied to the intake with the system running which will kill the mold and make the smell go away (at least for a while).

You can help prevent mildew from forming in the first place by robbing it of the moisture it needs to grow.  About 5 minutes before you reach your destination, make sure the vent is set to "fresh air" instead of "re-circulate."   This will help dry out the moisture that condenses in the vents.

[AT] Air for the climate control system gets sucked from the front of the windshield area under the hood on the right hand side. When you open the hood you can see the grate area on the passenger side near the windshield. Sometimes that strange smell may be coming from the drain pan under the air conditioner condenser and some minor mold may have collected there. I had some initially when I bought the car but after the first 3 months of use, it has disappeared and not returned.

[CA] I have a quick work around to this problem and it works pretty good. Start the car, put it on max A/C (re-circulate) and turn the heat all way up, the dry heated air will dehumidify the ac vents, leave it running for 10-15 minutes, you should not have a problem….also….when parking the car , put the vents on fresh air vs re-circulate, this will air out the system when not in use.

Sure this really is not any fun (read SUCKS) here in Dallas where we haven’t seen rain in a month and the temp is over 100 deg F everyday for the last few weeks, but……

[ST] Imparts has a Wurth product called PU (as in "this car stinks"l) $22 item# 39028 Phone 1-800-325-9043 FAX 1-800-525-9043. 

[GL] Instead of just spraying the cleaner from the interior air intake, it is more thorough to clean the evaporator. Accessing the evaporator for cleaning is pretty easy. You can access the evaporator from under the hood. Do the following:

  1. Remove spare tire and spare tire mounting bracket
  3. Disconnect battery and pull it forward to clear blower motor. No need to take the battery out and risk straining your back.
  5. Disconnect blower motor electrical harness.
  7. Remove Blower motor (4 bolts)
  9. After the blower motor is removed, you can see the condensor so start cleaning away.

This procedure is illustrated in the service manual under "Blower Removal". It is pretty straight forward and will ensure a thorough evaporator cleaning to eliminate A/C odors.

[MCO] I just bought my NSX a few weeks ago and the AC smell was very bad. I live in Atlanta and the humidity is really high. My solution was to always run the AC on recirc. This way it dries out the air and keeps it dry. If I take in outside humid air, the moisture is really bad and the smell is bad. In addition, running the AC on recirc keeps the car nice and cool. Ever since I started running it on recirc, I have not had any problems with bad smell.

[MJ] I was at CUSH Acura the other day and saw them doing an A/C "flush-n-clean" with something that is supposed to clean out all the cigarette smoke, dust, mildew etc. from your A/C system. It was called "DWD2" I was blown away at how well it worked. It is a dealer type item in that they drill a small hole in the evaporator box and blast it through the system, then plug it. CUSH does it for $79.95 – you might ask your dealer if they can do it too.