Honda Air Conditioning / HVAC - intermittent hot air

Adam Owner/Technician United Kingdom Posted   Latest   Edited  

Hi Gents,

Got a Honda Civic in the workshop with an intermittent AC/HVAC fault.

DETAILS:

  • Make/Model: Honda/Civic
  • Engine: 1.8 L
  • Fuel: Petrol
  • Year: 2008
  • BHP: 140
  • Engine Code: R18A2
  • VIN: SHHFK27408U019524

Customer reports that if you set the AC to ON and temperature to COLD, the car does cool correctly for a while but eventually will start blowing warm air (despite the control being set to cold, not "Auto"). 

In the workshop we have confirmed the correct AC fill level and that temperature at centre vents is correct at both full cold settings and full hot settings (see attached). There are no faults stored on the HVAC module and live data, while limited, does not raise any cause for concern. 

As the reported fault is intermittent in nature, we have not managed to experience things going wrong ourselves. Clearly there are a few things that could be causing this fault (intermittently defective temperature blend-flap servo motor; intermittently defective input sensor; etc), however was wondering if any of the community here could advise of any common issues or released bulletins to shed some light on a likely cause/s - I'm reluctant to speculatively strip, test and check on this one (we are German car specialists and don't hold powerful stats on the brand).

Thanks in advance. Adam

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Tyler Technician
Nova Scotia
Tyler Default
 

You could be on the right track with the blend door but these cars do have a high failure rate of the a/c clutch relays and the a/c clutch itself.

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Adam Owner/Technician
United Kingdom
Adam Default
 

Thanks mate. Yes, I did check it's operation and all was well, but as you say...could be dropping out and cutting the AC mid-journey? Perhaps what is muddying the waters here is that the customer is saying it starts blowing "hot" air...Perhaps "ambient" air, on a hot day, would be more accurate (and could suppose an AC issue rather than a temperature blend issue). For the low money and frequency…

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Jim Owner/Technician
North Carolina
Jim Default
 

I have a lot of these coming in with the following: 1) Bad clutch coil, 2) faulty a/c clutch relay, 3) intermittent expansion valves sticking, Try and reproduce the problem, it's the only way to narrow it down, (I have not seen any with a bad blend door)

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James Owner/Technician
Indiana
James Default
 

I have seen many clutch coils be intermittent on Honda.

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Craig Technician
Tennessee
Craig Default
 

I'll agree with the other comments. Compressor clutches and relays are very high failure items. Clutch gets hot after running a while and then will disengage and not have enough strength to come back on. I usually test by swapping the clutch relay with another one in the fuse box and see what happens.

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Randy Diagnostician
California
Randy Default
 

Check clutch air gap . And put a amp clamp connect it to a scope on clutch coil feed if it is the clutch this test will pick it up

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Jj Technician
Massachusetts
Jj Default
 

Clutch coil is super common on these. Let the car idle and put the blower on low with the a/c on. This will make the compressor cycle more often. Then if the compressor fails to cycle on at some point check relay operation, if the relay checks out ok reach down with a piece of wood or a bar and give the faceplate on the compressor a tap. If it engages you have a weak field coil.

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Adam Owner/Technician
United Kingdom
Adam Default
 

Great information guys - most grateful to all. I shall update here when further on (car to return for future booking)

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Luis Technician
California
Luis Default
 

A/C Clutch relay very common to stop working after extended period time being used, make sure to get factory genuine relay no aftermarket if you find relay failing also like everyone said compressor clutch/coil are high failure. do you have access to scan data to read evaporator temp sensor to make sure is not reading negative temperature causing to shut off compressor

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Adam Owner/Technician
United Kingdom
Adam Default
   

More fantastic information. Thank you.

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Sean Technician
Ohio
Sean Default
 

Have had quite a few acuras and hondas only acted up once warmed up, letting idle about an hour then the clutch or relay would finally fail.

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Lane Mobile Technician
Kentucky
Lane Default
 

You have probably got your answer with the other reply's. Clutch issues are very common (relay/clutch). One further thing is possible, moisture in the system freezing the expansion valve. If the problem occurs at higher speeds or after driving on xway, then it's highly possible. I have seen this issue multiple times on Hondas/Acuras. The fix is to reclaim, pull a deep vacuum (1 hour plus) and…

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Nelson Diagnostician
North Carolina
Nelson Default
   

Honda issued a TSB a few years back covering MY2008 and others pertaining to faulty AC clutch relays causing problems, among them, parasitic drains after the ignition was switched off. This was not one of your complaints with the system, but this relay is known for being weak. You might want to check to see if you have the upgraded AC relay in use to help rule that out as being the culprit…

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Luis Technician
California
Luis Default
 

Hi Adam can you post and update is vehicle fixed?

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Adam Owner/Technician
United Kingdom
Adam Default
 

Hi Luis, Waiting for the customer to book back in for further investigation. Scope at the ready.

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Adam Owner/Technician
United Kingdom
Adam Default
 

Quick update: Car back in our workshop. Initial testing points to likely clutch coil failure (after a period of correct operation). Will try to capture failure on scope in next day or two. Will post back.

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Adam Owner/Technician
United Kingdom
Adam Default
 

SOLVED: Confirmed compressor clutch defective.

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