New 'How Cold Is Air Con' Thread

[BongoMTBer]

As the old one was closed, I thought I would get back to the original topic.

At present, my air con works as it should. I press auto (climate control model) and this is what happens.

An electromagnetic clutch engages and spins the compressor up, at the same time, the rad fans kick in. The refrigerant gas is compressed which makes it hotter than the ambient air temperature. This is passed into the condensor matrix at the front of the car and cooled by the radiator fans reducing the temperature. The refrigerant then passes into the expansion valve which attenuates the flow of coolant around the system causing increased pressure upstream and reduced pressure downstream. From here it is allowed to expand and flow into the evaporator. The temperature lost in the condenser matrix equates to the loss of heat in the evaporator. Warm cabin air is passed over this where the heat is extracted from the air flow as it is cold. The refrigerant exit temperature from this evaporator is monitored by a thermostat which controls the fans and electromagnetic compressor clutch. When this temp is low enough, the fans and compressor will disengage until the evaporator temp increases again. This cycle repeats and hence modulates the evaporator cooling matrix at a fairly steady state of cooling. Warmer air is provided by mixing warm air from the heater to ensure the selected cabin temp is reached whilst still benefitting from the dehumidifying effects of the air con.

With my Bongo the fans kick in and out in time with the compressor. After inital cooling, approx 20 sec on and 20 sec off in the summer. Although I have not had a look, I believe that this is the radiator fans. The fans still kick in and out when the vehicle is moving, I can tell this by the voltage drop (on my added volt meter).

In short, when the air con is first put on, the fans should run up immediately until the evaporator (cooling matrix) reaches a set temp. The compressor clutch will then disengage and at the same time the fans will stop. With warm air passing over the matrix, it will then start to warm again. The rise in temp will eventually be sensed and the cycle will start again with the fans and compressor kicking in again to reduce the matrix temp.

If you listen to the fans going on and off, on a hot day you will hear more 'on' time than on a cold day.

Even with the fans running continually, there will be no danger of overcooling the engine, as the coolant thermostat only allows coolant into the radiator matrix when the engine is up to running temp.

If your system is not cooling as it should, it could be one of several things that have let you down.

1. Fans not running (fuse etc.)
2. Compressor not compressing (failed clutch/electrical connection)
3. Gas leaked out
4. Fungal/cruddy build up on the evaporator

I would personally look at the evaporator. That can be got at through removing the blower fan under the bonnet. Mine was clogged with Japanese insects and after cleaning with a stiff brush and Detol worked significantly better.

Good luck,

Sam.

[mister munkey]

Good info there Sam.

[kelv]

Very interesting Sam.
Many other cars have a "low" setting to sort of give a boost to the cooling activity before a more "reasonable" temp of say 18 deg C is selected as a maintenance temp to drive around at.
The Bongo does not have this feature, which means it takes longer to cool inside initially.
Especially as it has capacious inside dimensions coupled with a fair amount of glass which ensures that it will be baking inside if left in the sun, although privacy glass probably helps to reduce the "storage heater " effect.

Do you have any idea on how to maybe electronically lower the minimum temperature setting from 18 deg C to make cooling more effective initially ?
Would be useful.

[BongoMTBer]

Do you have any idea on how to maybe electronically lower the minimum temperature setting from 18 deg C to make cooling more effective initially ?
Would be useful.

I don't know but I would suggest that it cannot be electronically controlled any lower. The limiting fator is how cold the cooling matrix will go and how much air it can pass through. I would imagine that the system is designed to cool as low as possible before the humidity in the air starts to freeze on the evaporator matrix, eventually blocking it.

When set to 18, I would imagine that no warm air off the heater is being fed into the cabin on a warm day as the cabin temperature sensor (located behind 10 mm sq. grill left of radio) is registering above the selected temp.

Therefore, a lower temperature could only be achieved by fitting a larger evaporator and passing more air through it.

[BongoMTBer]

As an aside, I am sure our Yaris has a more sophisticated system in that the compressor does not seem to kick in and out. I can only assume that it modulates its output according to evaporator temperature. This is how modern aircraft conditioning systems work, making them more efficient.

[kelv]

Doesn't sound like a routine kind of modification then

I will just carry on parking it in the shade, or opening the window a litle at first in order to overcome the systems limitations.

Many thanks anyway Sam.

[BongoMTBer]

Doesn't sound like a routine kind of modification then

I will just carry on parking it in the shade, or opening the window a litle at first in order to overcome the systems limitations.

Many thanks anyway Sam.

Yep, that is what I do. Mine is black too!

[kelv]

Nice and hot then with the black.
Also, great to fun to keep clean I expect

[Jon 41]

Thanks for the detailed info BongoMTBer:
So if the radiator fans don't kick in when the aircon kicks in, but kick in normally when the engine coolant requires them to, thus eliminating fuses, relays, faulty fans etc. Have you any idea what the cause could be?

[BongoMTBer]

Thanks for the detailed info BongoMTBer:
So if the radiator fans don't kick in when the aircon kicks in, but kick in normally when the engine coolant requires them to, thus eliminating fuses, relays, faulty fans etc. Have you any idea what the cause could be?

Erm, no. Not without looking at a schematic or wiring diagram anyway.

I am not sure what does the controling of the a/c system, ECU maybe?

Didn't someone say that the fans run at 1/2 speed with a/c on? Is this fact or a guess? If so, it may be wired so that in a/c mode they are wired in series. Make sure when the fans kick in when the coolant requires it that they are both running. A failed motor wired in series will stop the other running.

Sorry I cannot help there, but I would need to either take mine apart or read a manual.

[BongoMTBer]

Jon, just read your post in the original thread. It was you that said they were supposed to run at a lower speed

Anyway, sounds like the fans are triggered by a pressure switch which is monitoring the pressure of the refrigerant. When the compressor runs, pressure increases in the condenser activating the px sw. This will almost certainly activate a relay. So, you need to trace the loom, carrying out continuity checks at each plug until you find the culprit. Could be a dead relay or dodgy loom/connection.

If the reduced motor speed is gen, the failed motor theory will still stand however. Otherwise, look for a resistor pack somewhere underneath and do a con. check on that too.

I am jealous of your juicy snag. Sounds like my idea of fun!

[BongoMTBer]

Got me interested now. I will have look at mine tomorrow.

[BongoMTBer]

OK, had a look.

The brown plug on top of the receiver dryer certainly has a part in fan operation. However, I think that this just looks at the system pressure and is what stops it working when it needs a charge. When disconnected it stops not only the fans from running but also the compressor too.

However, I have found the relay.

Under the bonnet, behind the right hand headlamp, in front of the battery, there are two rectangular boxes. Remove the lid of the one closest to the batt. There are three relays and the one furthest on the right controls the fans with the a/c on. Remove the relay and replace it with the one next to it and see if that gets the fans running. I tried this with mine and the fans worked with the newly slaved in relay. This should highlight if your relay has failed.

[Jon 41]

Thanks for all the info BongoMTBer, I tried the relays you suggested but to no avail. But good news, after further checks and generally jabbing a power probe around I found the problem. Rather than try to explain everything in this post I will post a link to a detailed info sheet with pictures. Once I found the fault I started taking pics for a step by step guide for anyone else with the same problem. I'll edit it and post the link as soon as I can.

Again thanks for all your help you managed to get the old grey matter going in a different direction.

The main thing is my aircon is now freezing cold, even stationary in traffic

[BongoMTBer]

Good news, I look forward to hearing the reason.