AC Help

[GGawaran]

P/N RECIRC MOTOR 79350-SL0-A01

Vehicle info: 91 5MT 234k miles

Tried searching and most of what I find is issues with the control unit after failure being stuck on max or low. CCU Unit was repaired sometime last year per the previous owner and seems to be functioning as intended however the air flow is just not very strong.

We looked at the different fuses associated with the system and found the high blower relay causing a bit of the issue but still doesn't blow very hard. Is it possible the blower relay or main blower fuse need to be replaced as well or if the blower itself it's showing its age?

 

[Honcho]

The first thing you should check is to change the setting to recirc mode and see if it blows harder. The NSX has a "90's Honda" A/C system, in other words, kind of weak and just barely adequate. On "fresh air" mode, the blower fan has to fight against cabin pressure and the flow, even at max fan, is fairly weak. This is most prevalent on a NSX that has had its door seals replaced and is well-sealed against the outside. When you switch to recirc, the fan should blow much harder, since it's just recycling cabin air. If that happens, the system is functioning normally.

If not, then you're on the right track. You must fist verify the electrical path to the blower via the fuses and relay. If those are good, then the blower motor could be failing...it's 30+ years old after all.

 

[GGawaran]

Yeah it does change when moving to recirc vs fresh air option. I just feel like it's still on the lower end side. My brother had a 91 accord and was using that as a comparison. Just wanted to see what others might have to say before taking out the blower motor.

 

[GGawaran]

The first thing you should check is to change the setting to recirc mode and see if it blows harder. The NSX has a "90's Honda" A/C system, in other words, kind of weak and just barely adequate. On "fresh air" mode, the blower fan has to fight against cabin pressure and the flow, even at max fan, is fairly weak. This is most prevalent on a NSX that has had its door seals replaced and is well-sealed against the outside. When you switch to recirc, the fan should blow much harder, since it's just recycling cabin air. If that happens, the system is functioning normally.

If not, then you're on the right track. You must fist verify the electrical path to the blower via the fuses and relay. If those are good, then the blower motor could be failing...it's 30+ years old after all.

Well I decided to double check things on the way home and it seems like the Recirculate / Fresh air option doesn't really change. Tested the windshield defrost and it diverted the air but recirc / fresh air options didn't really change anything. Where / what should I check to confirm what might be causing the issue?

 

[Honcho]

If that's happening, then it's probably your blower motor. I'd make sure to test the relay and fuse first to ensure they are fully functional and also check the fan control unit for soldering cracks. If all that checks out, it's the motor.

 

[Old Guy]

We looked at the different fuses associated with the system and found the high blower relay causing a bit of the issue but still doesn't blow very hard. Is it possible the blower relay or main blower fuse need to be replaced as well or if the blower itself it's showing its age?

What does 'bit of an issue' mean? The high blower relay only operates when the fan speed is set to max. If you notice no difference when switching to max then the high relay may not be operating. It is not the fuse. There is only one fuse for the blower and if it had popped then you would have no air flow at all.

At 234 k miles it is possible that the blower motor is ageing and that worn brushes may be causing an unintended voltage drop at the commutator which is dropping motor speed. With the fan speed set to max and the engine running, use a voltmeter and back probe the connector to the blower motor to measure the operating voltage at the motor terminals. The vehicle running voltage should be about 14.5 volts. If the voltage at the motor terminals is around 14.5 volts and the air flow seems poor you might have an ageing blower motor. If the voltage is significantly less than 14.5 volts you have a separate electrical issue and the first place I would look is at the blower high relay and the socket for the blower high relay - look for signs of overheating such as burning of the contacts or melted plastic.

Before messing with the blower motor, make sure that the mode motors that control all the HVAC flaps are operating. There is a self test feature in the climate control unit that you can use (get the service manual - page 22-12) to check the motors. With the blower motor on low you can also feel & listen to confirm that the flaps are opening and closing as you cycle through the positions. Feel for air flow because the self test is supposed to detect stuck flaps; but, if the linkage is broken the self test will not detect that.

The NSX HVAC remained fundamentally unchanged during the production run. The temperatures around here have been popping up into the low - mid nineties lately and the AC on my 2000 has no problem turning the car into a meat locker / beer chiller in less than 5 minutes of operation. If I select both the floor and dash air vents, air flow on max is sufficient to make the car uncomfortably cold very quickly. Based upon my experience I would not describe the OEM blower as weak.

 

[GGawaran]

What does 'bit of an issue' mean? The high blower relay only operates when the fan speed is set to max. If you notice no difference when switching to max then the high relay may not be operating. It is not the fuse. There is only one fuse for the blower and if it had popped then you would have no air flow at all.

At 234 k miles it is possible that the blower motor is ageing and that worn brushes may be causing an unintended voltage drop at the commutator which is dropping motor speed. With the fan speed set to max and the engine running, use a voltmeter and back probe the connector to the blower motor to measure the operating voltage at the motor terminals. The vehicle running voltage should be about 14.5 volts. If the voltage at the motor terminals is around 14.5 volts and the air flow seems poor you might have an ageing blower motor. If the voltage is significantly less than 14.5 volts you have a separate electrical issue and the first place I would look is at the blower high relay and the socket for the blower high relay - look for signs of overheating such as burning of the contacts or melted plastic.

Before messing with the blower motor, make sure that the mode motors that control all the HVAC flaps are operating. There is a self test feature in the climate control unit that you can use (get the service manual - page 22-12) to check the motors. With the blower motor on low you can also feel & listen to confirm that the flaps are opening and closing as you cycle through the positions. Feel for air flow because the self test is supposed to detect stuck flaps; but, if the linkage is broken the self test will not detect that.

The NSX HVAC remained fundamentally unchanged during the production run. The temperatures around here have been popping up into the low - mid nineties lately and the AC on my 2000 has no problem turning the car into a meat locker / beer chiller in less than 5 minutes of operation. If I select both the floor and dash air vents, air flow on max is sufficient to make the car uncomfortably cold very quickly. Based upon my experience I would not describe the OEM blower as weak.

Sorry when I say fuses and relays they all converge as the same thing in my head. Brian K was nice enough to send me schematic of the Higher Blower Relay and Blower Relay, the Higher Blower relay casing was damaged but potentially still good. It may have been placebo but after replacing the higher blower relay it felt "stronger" which is what I meant by a bit of the issue.

I'll need to get a volt meter so I can check the voltages (electrical is admittedly my weakest knowledge wise when it comes vehicles.)

As far the as the doors opening, I did a self check just to see if the vents were moving and I can confirm diverting air to the windshield, and the different positions work (front, legs, legs and windshield)

Outside of replacing the high blower relay, I will take a look for any damage / melted plastic.

Thanks! Will report back when I have time to check said items.

 

[GGawaran]

What does 'bit of an issue' mean? The high blower relay only operates when the fan speed is set to max. If you notice no difference when switching to max then the high relay may not be operating. It is not the fuse. There is only one fuse for the blower and if it had popped then you would have no air flow at all.

At 234 k miles it is possible that the blower motor is ageing and that worn brushes may be causing an unintended voltage drop at the commutator which is dropping motor speed. With the fan speed set to max and the engine running, use a voltmeter and back probe the connector to the blower motor to measure the operating voltage at the motor terminals. The vehicle running voltage should be about 14.5 volts. If the voltage at the motor terminals is around 14.5 volts and the air flow seems poor you might have an ageing blower motor. If the voltage is significantly less than 14.5 volts you have a separate electrical issue and the first place I would look is at the blower high relay and the socket for the blower high relay - look for signs of overheating such as burning of the contacts or melted plastic.

Before messing with the blower motor, make sure that the mode motors that control all the HVAC flaps are operating. There is a self test feature in the climate control unit that you can use (get the service manual - page 22-12) to check the motors. With the blower motor on low you can also feel & listen to confirm that the flaps are opening and closing as you cycle through the positions. Feel for air flow because the self test is supposed to detect stuck flaps; but, if the linkage is broken the self test will not detect that.

The NSX HVAC remained fundamentally unchanged during the production run. The temperatures around here have been popping up into the low - mid nineties lately and the AC on my 2000 has no problem turning the car into a meat locker / beer chiller in less than 5 minutes of operation. If I select both the floor and dash air vents, air flow on max is sufficient to make the car uncomfortably cold very quickly. Based upon my experience I would not describe the OEM blower as weak.

Will the self test also detect if its not moving from fresh air / recirculate?

Looks like it will test that as well.... will report what we find after the diagnostic

 

[Old Guy]

the Higher Blower relay casing was damaged but potentially still good. It may have been placebo but after replacing the higher blower relay it felt "stronger" which is what I meant by a bit of the issue.

Damaged - as in superficial damage to the case or it looked like the plastic might have got warm and softened? If it looks like the relay got hot then it is a trip to the garbage can for that relay even if it passes the nominal function test in the service manual. If it looks like the relay got hot, take a very close look at the socket in the relay box. Relay failure rates are low; but, when you do have one it not uncommon for the source to be a high resistance contact causing heating where the male spade terminals on the relay insert into the socket. That can melt the plastic in the socket base.

 

[GGawaran]

Damaged - as in superficial damage to the case or it looked like the plastic might have got warm and softened? If it looks like the relay got hot then it is a trip to the garbage can for that relay even if it passes the nominal function test in the service manual. If it looks like the relay got hot, take a very close look at the socket in the relay box. Relay failure rates are low; but, when you do have one it not uncommon for the source to be a high resistance contact causing heating where the male spade terminals on the relay insert into the socket. That can melt the plastic in the socket base.

It looked like someone had grabbed it with long pliers and cracked the plastic.

 

[GGawaran]

Update on what the diagnostic found / lack there of.

So I followed the directions putting it into auto and setting the temperature to 64 for at least a minute, and then moved it to 90 for at least a minute and pressed auto and off at the same time. Nothing triggered or showed so I thought I did it wrong and did it while it said "full auto" instead, again I got nothing showing any of the potential error codes.

So I decided to run the other diagnostic and press and held auto and mode while I started the car. it ran through 88 1,2,3,4,5,6,7,8, 88

To my surprise the air was blowing a lot harder during phase 4 and 5. Let it cycle a couple of times and turned off the car. Got some things out of my office and left and now it's blowing a lot stronger overall.

Question now is either I am doing the diagnostic right and there is nothing reporting and everything is fine... or I did it wrong and there could still be something wrong.

While I do notice the stronger flow of air, the strength does not change when I select recirculate or fresh stays consistent air flow wise.

Based on Old Guy and his description of the AC I am venturing to say its stuck in fresh air mode because at night when the temperatures drop it does got a lot cooler vs during the day (90-95 degrees here in Dallas atm)

 

[Old Guy]

So I followed the directions putting it into auto and setting the temperature to 64 for at least a minute, and then moved it to 90 for at least a minute and pressed auto and off at the same time. Nothing triggered or showed so I thought I did it wrong and did it while it said "full auto" instead, again I got nothing showing any of the potential error codes.

You did it correctly. Nothing illuminating means everything that it could test is OK

So I decided to run the other diagnostic and press and held auto and mode while I started the car. it ran through 88 1,2,3,4,5,6,7,8, 88

To my surprise the air was blowing a lot harder during phase 4 and 5. Let it cycle a couple of times and turned off the car. Got some things out of my office and left and now it's blowing a lot stronger overall.

Compared to the other steps in the operation check, steps 4 and 5 will blow a lot harder out the dash vents because;
- it has shut off air flow to the floor vents
- it has switched to recirc and
- the fan is switched to high.

Question now is either I am doing the diagnostic right and there is nothing reporting and everything is fine... or I did it wrong and there could still be something wrong.

I think your test procedure was correct

While I do notice the stronger flow of air, the strength does not change when I select recirculate or fresh stays consistent air flow wise.

Based on Old Guy and his description of the AC I am venturing to say its stuck in fresh air mode because at night when the temperatures drop it does got a lot cooler vs during the day (90-95 degrees here in Dallas atm)

With key to run; but, engine off, turn the CCU on with AC off and set the fan speed to slightly less than 1/2 max. Press the recirc button. Wait 10 seconds and press the fresh air button. You should hear a slight thud as the recirc door moves after 1-2 seconds. Wait 10 seconds and the press the recirc button and you should hear a slight thud again as the door changes position. If you hear the thud when you switch from fresh to recirc the fresh / recirc function is probably working. The fan speed has to be fairly low in order to be able to hear the flap move.

As a final thought. Your car qualifies as high use vehicle. Unlike more modern cars the NSX does not have a cabin air filter which means that whenever the blower is operating in fresh air mode it is sucking in garbage from outside the car and depositing it on the front of the evaporator core which can restrict air flow under all conditions. It also accumulates dirt on the actual blower element. You can clean the front surface of the evaporator; but, it requires removal of the blower housing from the HVAC unit which means that you can also clean the blower.

 

[GGawaran]

With key to run; but, engine off, turn the CCU on with AC off and set the fan speed to slightly less than 1/2 max. Press the recirc button. Wait 10 seconds and press the fresh air button. You should hear a slight thud as the recirc door moves after 1-2 seconds. Wait 10 seconds and the press the recirc button and you should hear a slight thud again as the door changes position. If you hear the thud when you switch from fresh to recirc the fresh / recirc function is probably working. The fan speed has to be fairly low in order to be able to hear the flap move.

yeah no noise or movement when trying the recirc / fresh. To see if any movement was going I tried the defrost and heard the flap / motorized movement and air flow changing. I wonder if the motor is good and the flap is jammed or broken.

As a final thought. Your car qualifies as high use vehicle. Unlike more modern cars the NSX does not have a cabin air filter which means that whenever the blower is operating in fresh air mode it is sucking in garbage from outside the car and depositing it on the front of the evaporator core which can restrict air flow under all conditions. It also accumulates dirt on the actual blower element. You can clean the front surface of the evaporator; but, it requires removal of the blower housing from the HVAC unit which means that you can also clean the blower.

Yeah my intention at some point was to remove the blower and clean it out. What I wasn't aware of is that it would allow access to the evap core to clean it out.

That being said hopefully access to the recirc motor isn't too much of a trivial thing. I am surprised that the blower is much stronger now after doing the auto / mode diagnostic because it is overall blowing stronger than it did prior to doing it.

 

[GGawaran]

I'm tackling this and a few other things as this is technically my daily driver right now and when we start hitting high 90s low 100s it's gonna suck haha

 

[GGawaran]

Looks like it's connected to the blower motor casing per 22-64 of the service manual. There's a few other things I can test I just need to get the correct tools and get to the harness behind the ccu.

 

[Old Guy]

It looks like you have already discovered that the recirc control motor is probably the only flap control motor on the NSX that is moderately easy to get at.

 

[GGawaran]

It looks like you have already discovered that the recirc control motor is probably the only flap control motor on the NSX that is moderately easy to get at.

i'll count it as an early blessing. Once I get the blower off and test the motor ill report back here for others who may be running into the same issue. Are these motors able to be rebuilt or am I better off just getting a new unit while they are available from Honda?

Thanks in advance!

 

[Honcho]

i'll count it as an early blessing. Once I get the blower off and test the motor ill report back here for others who may be running into the same issue. Are these motors able to be rebuilt or am I better off just getting a new unit while they are available from Honda?

Thanks in advance!

The motor is easy to remove and you can replace the brushes (I think @drew has the dimensions), which are usually what causes it to fail. Also, members have reported much faster running once they clean out all of the black gunk from the motor housing even without replacing the brushes. Please post pics when you do it. You can pop off the back cover of the motor to get to the brushes and area to clean.

 

[GGawaran]

The motor is easy to remove and you can replace the brushes (I think @drew has the dimensions), which are usually what causes it to fail. Also, members have reported much faster running once they clean out all of the black gunk from the motor housing even without replacing the brushes. Please post pics when you do it. You can pop off the back cover of the motor to get to the brushes and area to clean.

Will do! I have a bunch of pictures and a thread i need to post about getting the car and what not but just been busy tackling a lot of small things.

I've had the car 3 weeks ish and put just about 2000 miles on it.

 

[Old Guy]

i'll count it as an early blessing. Once I get the blower off and test the motor ill report back here for others who may be running into the same issue. Are these motors able to be rebuilt or am I better off just getting a new unit while they are available from Honda?

Thanks in advance!

Are you talking about the blower motor or the recirc flap motor? As Honcho notes, you can replace the brushes and clean up the commutator on the blower motor. The brushes are not available from Honda; but, there are a couple of companies that specialize and stock a huge range of brushes in various sizes. People have used them to rebuild the condenser fan motors. I have never heard of anybody rebuilding a flap control servo motor.

 

[GGawaran]

Are you talking about the blower motor or the recirc flap motor? As Honcho notes, you can replace the brushes and clean up the commutator on the blower motor. The brushes are not available from Honda; but, there are a couple of companies that specialize and stock a huge range of brushes in various sizes. People have used them to rebuild the condenser fan motors. I have never heard of anybody rebuilding a flap control servo motor.

I was curious if it was possible. I picked the servo motor up from amayama for 67 dollars vs trying to buy it here stateside for over 300.

 

[GGawaran]

I've got a lot of photos so ill update them here when I get them uploaded to google drive.

I completely disassembled the blower motor assembly and redid all the seals I could (foam insulation) on every part that I saw had something on it.

Replaced the recirc motor put it back together and the air flow seems a bit better, but the recirculation button still feels like it's not working.
Set it the the lowest setting and I couldn't hear the "audible thump" that old guy was mentioning.

I tried to look through the service manual but I couldn't find anything in regards to a relay or fuse or anything for the recirc motor.

I double checked the relays again and the blower high relay which I recently replaced is warm ish, nothing crazy but the blower relay is extremely hot.

Next step do I replace and blower relay?

And two, I don't know what else to check as to why the recirc motor won't engage

 

[Old Guy]

If the blower relay is extremely hot I would replace the relay ASAP. A hot relay is an indication that the primary contacts in the relay or the terminals that connect to the socket have developed significant resistance which is generating heat and reducing the voltage available to the blower motor. Check the terminals in the socket for signs of damage due to heating. I like to apply Ox Gard or De Oxit to the terminals that go into the socket to enhance the connection.

If replacing the blower relay does not resolve the problem. Then consider the following.

There is no specific relay or fuse for the recirc servo motor. It is directly controlled by the CCU.

If you look on page 22-89 you will find the test for the recirc flap servo motor. You need a multimeter or a continuity tester; but, that test will confirm that the servo motor is working and that the contacts associated with the fresh air versus recirc air flap position are functioning. The position switches are built into the motor assembly so the fact that the switch contacts change status is not a 100% confirmation that the flap is moving. It is still possible that there might be a mechanical problem between the motor output and the flap resulting in non movement of the flap. You would have to visually inspect the flap mechanism to confirm that it is OK

If you have your old recirc motor, you could connect it up to the plug and operate the fresh / recirc buttons to confirm that motor is changing positions which confirms that the CCU is sending the open / close signal and the motor is receiving the signal; however, I would expect that error would have been caught by the CCU self test function.

 

[GGawaran]

If the blower relay is extremely hot I would replace the relay ASAP. A hot relay is an indication that the primary contacts in the relay or the terminals that connect to the socket have developed significant resistance which is generating heat and reducing the voltage available to the blower motor. Check the terminals in the socket for signs of damage due to heating. I like to apply Ox Gard or De Oxit to the terminals that go into the socket to enhance the connection.

If replacing the blower relay does not resolve the problem. Then consider the following.

There is no specific relay or fuse for the recirc servo motor. It is directly controlled by the CCU.

If you look on page 22-89 you will find the test for the recirc flap servo motor. You need a multimeter or a continuity tester; but, that test will confirm that the servo motor is working and that the contacts associated with the fresh air versus recirc air flap position are functioning. The position switches are built into the motor assembly so the fact that the switch contacts change status is not a 100% confirmation that the flap is moving. It is still possible that there might be a mechanical problem between the motor output and the flap resulting in non movement of the flap. You would have to visually inspect the flap mechanism to confirm that it is OK

If you have your old recirc motor, you could connect it up to the plug and operate the fresh / recirc buttons to confirm that motor is changing positions which confirms that the CCU is sending the open / close signal and the motor is receiving the signal; however, I would expect that error would have been caught by the CCU self test function.

Yeah, when I did the test nothing happened, well nothing showed up which is why I thought I may have done it incorrectly when I posted about it a couple weeks back.

Thinking the diagnostic had not pulled anything up I just chocked it to a bad recirc motor. The only thing I didn't have access to was a way to test it before putting it back into the car. I had found the troubleshooting on 22-89 just had no way to test it with 12V power. Don't have a power probe or some connects to try it on hand. I'll try that again today as the blower is fully disassembled again.... waiting on the power probe to come in later today

Found out that the flap door needs at least 3/16ths for the insulator as 1/8ths is slightly too short and doesn't seal fully.

 

[GGawaran]

So my power probe came in today and found that both the old and new motor are working as intended. I then proceeded to test the harness that plugs into the motor, everything passed there as well.

That leaves me with a problem with the CCU, or the harness from the CCU to the recirc motor.

Not the best thing to find out, but I did power the motor to the recirc mode, in the event the CCU / harness is having issues at least it's stuck in recirc instead of fresh air.