Aircon clutch relay rec

[MartinJG]

I find the aircon does a great job of freezing the cabin at normal temperatures @ 22-24C but the moment we have hotter weather it struggles. This has been a recurring problem which I believe is down to the clutch relay which seems to malfunction when we get into the 25-30C range. The fan stays on but the clutch does not engage. Everything is fine when the temp drops below @ 25C. I replaced the relay two years ago but the hot weather issue still persists. Has anyone had a similar problem? Thanks

[GBH]

My first move would be to have the system pressures / refrigerant capacity checked.

Once had a problem with a SAAB while on holiday and went to nearby garage who employed an aircon specialist with all the proper equipment. Result was he found a wiring fault that was shorting out the pump clutch. The car was with them for over an hour but they only charged me for half an hour labour. Result was a nice cool interior.

[MartinJG]

We went through the usual dye test and found no leaks at all and the pressure is within the normal tolerance according to the equipment they use. The problem boils down to the fact that it doesn't seem to function properly when it gets very hot which is when it is needed most! The fan stays on but the clutch fails to engage on the compressor. I checked last night when the temp was 24C and it was working fine. I replaced the relay two years ago thinking that was the problem but the pattern of behaviour is exactly the same as before. It just doesn't like hot weather but we don't get too much of that so it's one of those infuriating intermittent issues. I am curious to know whether other Jazz owners experience this performance dropout when we get into the 25-30C territory. Thanks for your feedback.

[Marco1979]

What does your aircon radiator (next to the radiator for cooling the engine) look like? Sometimes most of the tiny metal studs can disappear over time, seriously limiting the amount of heat that can be transferred to the air, but not enough to cause a leak. It sounds like its capacity is severely limited 

[GBH]

To check if the outdoor temp. affects the performance I have just been out to my Jazz (which has sat outside in the road all morning) and used a thermometer in the face level vent.

Results: Outside temp 30 deg C
             Inside temp - didn't record that but couldn't touch the steering wheel!
             Face level vent output quickly dropped to around 5 deg C (in a matter of minutes).
So I would suggest that there is definitely a problem with your system as there appears to no restriction (within normal paramaters) on how much heat can be removed by a car A/C system.

I am wondering if the problem could be with the pump's clutch rather than the relay?

[GBH]

Having given this some thought over lunch, I know that you say that someone has checked the system pressures and they appear O.K. but from when I have visited a specialist I remember him re-charging my system by refrigerant weight, rather than pressure.

He used a small set of electronic scales (much like the bathreem variety) to determine the correct amount of refrigerant needed according to a book listing A/C systems by car make and model.

I also seem to remember an old BMW I had, having a specification plate riveted in the engine bay with the A/C specifications stamped on it, e.g. refrigerant weight (this was not long after the change in refrigerant type used in cars was mandated and I was having the system repaired & re-charged due to a slow leak).

[MartinJG]

What does your aircon radiator (next to the radiator for cooling the engine) look like? Sometimes most of the tiny metal studs can disappear over time, seriously limiting the amount of heat that can be transferred to the air, but not enough to cause a leak. It sounds like its capacity is severely limited 

Doesn't look too bad really. A couple of fins are bent but I think I can forgive it after 16 years of service .

See my latest post for troubleshooting update.

[MartinJG]

Update. Checked with Honda on logical analysis. They agree it points to the relay. As a footnote, Honda stockists now use Mitsuba and not the old OEM Omron which had problems with the seal. This was more damp related but if so, equally, it could allow external ambient atmosphere into the case which would affect the copper coil/switching mechanism. Furthermore, I noticed that the problem occurs when the car is at low speeds or stationery which suggests ram air helps to keep the relay switch cooler. I found that by switching off the aircon and leaving it for 5 minutes and then switching it back on while on the move activates the clutch and system then works as normal. The temp reading in the Jazz was 29C when I tested this. There was always a correlation with hot weather but I now believe I have narrowed down the problem to a faulty relay. Thanks to all for feedback. Hop this helps others with the same issue.

[Lord Voltermore]

If ram airflow improves the relay/clutch switching performance   it might be worth checking whether the cabin air filter needs replacing.     

I have also read that  A/C can only reduce the ambient temperature by about 20 degrees.  Reducing 30 ambient to 10 cabin will feel cold.   But 37 down to 17 wont feel as icy.
 

[MartinJG]

If ram airflow improves the relay/clutch switching performance   it might be worth checking whether the cabin air filter needs replacing.     

I have also read that  A/C can only reduce the ambient temperature by about 20 degrees.  Reducing 30 ambient to 10 cabin will feel cold.   But 37 down to 17 wont feel as icy.

Agreed. Cabin filter is OK. It never seems to collect much dirt but I change it every year anyway.

On the ambient temperature. Not surprisingly, the cool airflow is noticeably better at @ 50MPH+. Let's face it, that was all we had back in the day before aircon . However, when we get these baking hot days, the ordinary ram through the vents with the aircon off can actually be quite warm. Switch the aircon and I can immediately notice the chilled airflow. It might not be freezing cold but I will take plain chilled every day