Rover 75 aircon startup delay
 

Hi,

This has been annoying me for a while, so I thought I'd ask about it. I can't seem to find any other threads about this, so if you know of any, please link them :)

The problem is that there's often a delay from when the car starts and when the aircon (ventilation fan) starts. The delay can vary from a few seconds to a few minutes. Other times there's no delay at all. This is very annyoing, especially since my car is always full of condensation (and, if below zero, ice...)! :mad: Pushing different buttons (auto, demist, etc.) doesn't get the fan started either.

I haven't noticed any correlation between outside temperature or engine temperature and a/c startup. Once it starts, it works perfectly.

If relevant, I have the two speed radiator fan with gold resistor mod, and the radiator fan works just fine as far as I'm aware - the low speed activates immediately with ignition + demist.

Any ideas?

If the ambient temperature is very low and the aircon refrigerant/gas content is less than ideal, I could imagine that the trinary switch won't allow the system to start up cleanly. The trinary inhibits both too low and too high pressure situations from activating the compressor clutch. Maybe worth having the refrigerant checked/replaced.

TC

But ambient temperature doesn't seem to be a factor, the delay is there during the warmest of summer days too. And the a/c produces freezing cold air, so I don't think there's too little refrigerant. Is there a way to check this at home? What else could be wrong?

Arne,

Are you asking about the blower inside the car? It should activate straight away when you request air conditioning on "the warmest of summer days".

Try charging your battery externally for 24 hours. Some equipment can be inhibited after a cold start if the battery voltage falls below a certain threshold.

Simon

mine always takes a few seconds to begin ramping up to the speed the blower has been set at. Normally I would switch off the blower when I pull up for the evening, occasionally I would forget. So when I start the car the next day, after a few seconds I will realise the blower is ramping up to speed (normally switch it off then).

From that I noticed that when the engine is cold, the blower would take very slightly longer than it would if I had been driving. It doesnt start to ramp up until I have reversed out of my parking space. I have always assumed it was to do with the extra strain on the engine when cold. Cold oil plus the compressor running would create a little extra drag on the engine for those critical seconds to get the oil around it.

Take a note of it when the engine is cold, and when warm to see if there are variations. On mine there is, but it is small (1-5 seconds maybe), but then temps for me rarely get below freezing (and even rarer to get about 20 :mad:)

When the engine is warm and the ATC is set to auto, as mentioned it also takes in ambient temps when begins to ramp up the speed of the blower.

The gradual ramping of the blower on start up also makes it a little more pleasant compared to the shock of a instantly blaring blower :}

Yes, I think so? :o Are you asking about the ventilation fan? Sorry, I had to :D I'm not always certain about the terminology, so I went with what Jules called it in this post: How to test radiator fan speeds.

But no matter the temperature, it should activate immediately, no? Not necessarily in full hair dryer mode, but a small breeze. Yet for a few seconds or minutes there's no "blowing" whatsoever, whether I use auto, manual or demist.

I've charged my battery several times this winter, and changed it too (for other reasons). It doesn't make a difference :(


Mine ramps up too, but only after the delay during which it's completely dead. I'll try to be more scientific about it though, maybe a pattern will emerge ;) But my impression is that the delay is fairly arbitrary in occurence and duration, not having to do with ambient or engine temperatures. Besides, the variations we're talking about aren't seconds, but minutes :( Sometimes I can drive for a couple of miles with an already warm engine on a hot summer's day before the blower starts up, while other times it starts as soon as I start the car, even on a cold day with a cold engine :shrug:

I still think it is worth getting the A/C charge checked out, even a system 50% full will still blow very cold but the trinary switch will be struggling to get enough pressure. It could even be a dodgy trinary switch, I had one to fix recently that one day was ice cold and another it was reacting like it had no refrigerant, a knock on the trinary would bring it back to life.

Some places advertise they wont charge unless they make your system x degrees colder so if there is nothing wrong it wont cost.

The internal ac/heater blower should normally start straight away normally at the lowest speed with a cold engine: it'll increase as the engine warms up or if asking for air colder than outside it'll increase as the air-conditioning becomes effective. if you press demist it should go to full - does yours? I suspect your lowest speed isn't working, try taking manual control of the fan speed and see if the lowest speeds are pushing any air through.

What were the symptoms of the dodgy trinary switch? Did the blower work only intermittently? Because mine works continually after the initial delay. I prefer to investigate other options before checking/refilling the refrigerant, because that'll probably be £100 :( I live in Norway you see...

The blower goes to full when I press demist, yes. And all the lower speeds are working too. As far as I can tell, there's absolutely nothing wrong with the a/c once it activates, it's just that it takes a while before it does.

I'd have expected the interior blower to start immediately the aircon system is started. Logically the motor is OK, so I'd suggest looking at or swapping the speed control/transistor pack. This is just a plug'n'play module that you can buy from eBay.

TC