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A/C tale of woe: long post

18 October 2015
Cleveland area, OH
I am not sure how to articulate this as I’m not a mechanic, but I will try.

1999 NSX-T manual

On two long road trips this year, A/C was blowing ice cold early in the trip, then progressively the fan blower worked less well after about 1 1/2- 2 hours, until so little cool air was coming out that there wasn’t effective cooling.

The first time this happened, on my trip to Mid East Meet, on the advice of others, I purchased a recharge kit. However, when I placed the pressure gauge on the low port, it read as fully charged. I inserted a small amount of refrigerant, just a couple of squirts.

Same difficulty on the way home from Raleigh. 1 1/2 hours of ice cold, then minimal-no blowing air. I could turn fan all the way up to achieve some cooling for a short time afterward, but

Delayed in having AC looked at because of paint issues (long story, now resolved). However, same thing happened on a shorter (250 miles round trip) to Pittsburgh last weekend. This prompted me to get the system looked at by a professional. Unfortunately, Acura dealer with NSX specialist booked out for weeks and I had no time to send car down to Source 1, which I would ordinarily do. I therefore had a local automotive AC specialist take a look last week. No leaks found and compressor was working fine. Long road test (30 miles each way) showed normal function. Was decided based on experience with other Honda compressors to replace because he thought the coil might be going bad. I reluctantly agreed as I was in a hurry for resolution before long road trip to XPO. Big mistake. They had to modify the new compressor by placing the stock pulley/clutch from my old compressor onto the new one. Did this before I was told about it, I would have sourced the correct part.

To add insult to injury, I still have nearly, but not exactly the same problem. I had ice cold A/C for an hour into my trip to XPO, and now absolutely no air movement after that. Was a long, noisy day with the windows down as no working A/C. The difference now is that when I turn the fan all the way up, I have no airflow whatsoever. I can hear a fan on when I turn the fan switch.

If I were at home, I’d simply stop driving the car and have it shipped down to Source 1 to have it looked over by folks who know more about NSXs. Unfortunately, I am on the road now and I’ll have to “grin and bear it”.

I’ll run the CCU self test in the AM. I don’t think this is CCU related, it’s not what’s typically described. I’ll also look at the blower relay.

If anyone has any other ideas after reading this wall of text, I’m all ears. I’ll be at NSXPO track and social days if anyone wants to chat in person.
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[MENTION=32021]neuronbob[/MENTION] - need a little clarification. You said

"On two long road trips this year, A/C was blowing ice cold early in the trip, then progressively the fan blower worked less well after about 1 1/2- 2 hours, until so little cool air was coming out that there wasn’t effective cooling."

"Then progressively the fan blower worked less well" Does that mean that the air flow through the heater / AC system is actually reducing or that air flow is still the same; but, the air is no longer cold? If the air flow is actually reducing check by listening to the blower motor. Is the blower motor actually dropping in speed or does the blower motor seem to have the same noise level, just no air flow?

1) If the blower motor is dropping in speed then you may have a problem with the blower motor power transistor. The power transistor may be over heating after extended use reducing the voltage available to the blower causing it to drop in speed. Switching the fan speed to maximum on the CCU by-passes the power transistor and the fan speed should increase to maximum. If the fan speed does not switch to maximum then something else is the problem.

2) If the blower motor seems to operate as it should (the fan noise seems to be normal); but, you are getting reduced air flow and / or poor cooling you may have a severe case of evaporator icing which is restricting air flow and cooling. This would actually fit with your description that the problem does not emerge until after you have been driving for some period of time. You also live in Ohio which is a bit like living in a steam bath, at least for a guy from the prairies. High humidity will contribute to evaporator icing. I am not an AC guy; but, there is a temperature sensor in the evap and if the restricted air flow blocks heat transfer to the evap the CCU may shut the compressor off to prevent damage.

Are you getting a really big pool of water collecting under the car when it is parked? That would be an indication of ice accumulation in the evaporator. Normally, when the AC is running water from the air will condense on the cold evap fins and then drain off. I suppose that under really high humidity conditions the water accumulation rate could be high enough to result in ice build up. The other possibility is that your evaporator fins are really dirty and the dirt film is retaining the moisture which then freezes up leading to reduced / no air flow after a period of time.

If this problem reoccurs next time you drive, turn off the AC and let exterior air blow through the evap for a while. If you have icing this may speed up melting.
>Was decided based on experience with other Honda compressors to replace because he thought the coil might be going bad.

OK. Not sure what this has to do with the interior fan failing?

Regardless, replacing the coil is just that: replacing the coil. It can all be done in situ, remove the pulley (do loosen pulley nut with belt on), R&R the coil, and replace the pulley. One hour of shop time.

A good test prior to replacement is to bypass the relay, energize the clutch pulley, and see if the condition persists.

>They had to modify the new compressor by placing the stock pulley/clutch from my old compressor onto the new one.

This seems fine, did they put in the previous coil too?

>Big mistake.

Yes. Remember a professional does it for a living, it DOES NOT mean they know what they are doing.

I'm with Old Guy on the diagnosis and test tree.
Thanks for the replies. Kaz [MENTION=7722]Kaz[/MENTION]-knukNA1 and [MENTION=7588]Briank[/MENTION] have also chimed in via Facebook.
[MENTION=26435]Old Guy[/MENTION] , I can hear the fan working, but air flow is less. There was (prior to compressor change), a massive pool of water under the car every time I shut the car off. Since the new compressor, water is less but still present. I read your post from the road yesterday and immediately tried running for an hour with A/C mode off, and outside air on. No change.
[MENTION=5430]drew[/MENTION] , I know, huge error on my part, was in a hurry and it cost more money. UGH. Once I return from NSXPO, I’m going to find the time to get it down to Brian Urlage and crew at Source 1 for a proper fix.

Thankfully, don’t need A/C at an XPO track session :) .

To add some updates from my FB post, which was just a link to this thread…

Kaz suggested I perform the CCU Operation and Function test. CCU works fine as the blower motor changes speed as it is supposed to during the test. Test done early this AM on first start, though. I also did the self-diagnostic yesterday and came up with “A/C”, ie mix door stuck. Repeated this AM fresh, and no error.

Brian K indicates he had a similar problem to mine years ago, and that replacing his radiator fan control unit fixed it. He said:

“Most likely your evaporator core is freezing up and stopping air flow. The most common cause is the Radiator fan control unit is causing the compressor and condenser fans to run non stop. The ccu monitors the evaporator temp and turns off the compressor run request to keep the evaporator from freezing but that signal goes through the radiator fan control unit. Had this same issuer in my car many years ago and fixed the radiator fan control module and its been all good since.”

FB comments added here so the next guy troubleshooting this can find it. I found nothing in my exhaustive search of Prime.

So…now searching for said module.
The control arrangement for the AC is confusing. The fan control unit does have a connection to the CCU and the ECU (which controls the AC compressor). The service manual does not make it clear what the function of those connections is so the fan control may be getting a permissive from the CCU that it sends to the ECU to control the compressor.

If you do a Prime search on fan control units, you will find that they do have a bit of a reputation for flakey / intermittent operation. Most of these problems appear fixable by reflowing the solder joints on the circuit board so that may be a no cost repair. If you elect to replace rather than repair the fan control unit, I suggest you check the evaporator temperature sensor before replacing the board to rule it out as a possible cause (the test is in the service manual). A complete failure (open / short circuit) of the sensor should show up in the CCU self diagnosis check; but, if the sensor has just gone out of spec then the self diagnosis may not pick up the problem.

"I also did the self-diagnostic yesterday and came up with “A/C”, ie mix door stuck. Repeated this AM fresh, and no error."

It is possible that if you did the first test after the evaporator had iced up it was causing a problem for the mix door which resolved itself after the ice melter.
More, and interesting, updates.

Brian has a refurbished fan control module, which is en route to the NSXPO track day hotel and should arrive today. I’ll install it tonight, hopefully.

Once I arrived in The Dalles, in 100 degree heat, I started hearing an intermittent squeak from behind the firewall. Ultimately, any time I tried to apply power, I’d smell burning rubber and saw smoke. Fearing a seized alternator, I stopped the car immediately. Was next to an O’Reilly’s and had the alternator tested…”good”, for whatever that’s worth. Some kind passers by pushed my car out of traffic and at that time I inspected the AC belt. It was SUPER tight!

I sent out an SOS via Facebook and was soon helped to loosen the belt. All seems well for now. I was worried I fried the AC compressor too, but after about 30 miles of road testing, no issues.

So…yeah, I’m going to get that module installed as quickly as I can.
Hey @neuronbob what was the outcome?

When I was driving home from the GRM $2K challenge in Orlando the air coming out of my vents stayed cold on the way home but the volume of air through the vents steadily decreased even though the HVAC blower motor sounded fine.

When this happened my HVAC seemed to stop moving some of the internal flaps as well, even though the CCU buttons and LCD panel continued to work. I also noticed a larger-than-normal puddle under the car when I stopped for breakfast.

Anybody have additional advice, or should I just go ahead and pull the FCU from behind the seat and re-flow the solder?
The gradual decrease in air flow and larger than normal puddle under the car would be consistent with ice build-up on the evaporator which would restrict air flow and possibly prevent the vent motors from operating the flaps. The fan control unit has absolutely nothing to do with the volume of air flowing out of the interior vents so don't go fiddling with it expecting to address the interior air flow problem.

Let the car sit and the ice melt. That should resolve your interior air flow problem and vent motor control. If it doesn't then you have some other problem; but, it's not the FCU. By attempting to operate the vent flaps while they were jammed with ice you may have damaged the flap operating mechanism or the vent motors. If there is damage to the vent control reflowing the FCU is not going to fix that. The evaporator housing has an internal temperature measuring probe and part of its function is to try and prevent icing by shutting off the compressor. I can't remember whether there is an error code in the CCU for that sensor; but, running a function check on the CCU as described in the service manual might be a good plan.
You should have the a/c system properly evacuated and re charged to the proper level of freon and that could eliminate some of the problem. Short answer. The wrong level/amount of freon can cause the evaporator to ice up and be the cause of the freezing problems.
Kaz is the best resource for a/c information bar none. Keep in mind he's very covered up helping people with other problems.

Try and remember, don't change the crankshaft if it only needs an air filter.