Air Con: Has the heat killed it?

[dave lincs]

You are not far from Big Russ perhaps send him a PM and he will check the fan on T4 for you

[Arctic]

Originally Posted by TomTheTyke

Thanks again for the help. Interesting to learn how the system works. I suppose when I say 'hot' I mean 'ambient' air, it's just that it was hot yesterday!

This thread seems to be the best way to test operation? https://www.the75andztclub.co.uk/for...hlight=trinary

I've done plenty of mechanical tinkering but never messed about with electrics before!

You can check which fan you have by looking through the fron t grill at about 2 O-clock if it's a two speed fan you will see either a silver resistor or a gold one.
1

2

If a four wire three speed fan you will just see the bracket the resistor would fit to.

3

[TomTheTyke]

Seeing as I'm off work today, decided to have a little play with this.

Firstly, thanks Arctic, I do have a 3 speed fan, no resistor present.

So I followed the instructions on the thread above and bridged the pins with a paperclip to test Medium fan speed.

At first I turned the engine off between running the aircon on demist as normal, then with the pins bridged. I couldn't tell a difference which suggested the MED speed is duff.

But then when removing/replacing the bridge while the car was running and aircon on, I realised the speed of the fan WAS in fact changing, though it definitely wasn't night and day, it was speeding up with the bridge in place.

Condenser also looks OK as far as I can see, no big areas of damage or missing fins.

So the mystery goes on, again without conclusive proof of a T4 check on the fan / check of the system more generally.

[TomTheTyke]

Been thinking this problem over some more today, I like things to be right where possible and we are looking at taking the car to Europe next year; it would be nice to have the aircon working 100% then.

Thanks to the kind help from various members here it seems the basics are:

The aircon does blow cold but not when the system is under most load, e.g. helps to have windows open to draw air through in order to get going, and fails to cool air when no ram effect i.e. car is in hot weather and not moving.

Realistically it could be 3 things, as far as this thread has helped me understand, as Simon basically said above:

1. 3 speed fan. Seems to be working on speeds 1 and 2, although as above I found it quite difficult to determine for speed 2. Is it possible 1 and 2 could work but top speed has gone, hence why it doesn't blow cold when needing most demand, stood still in the heat? This actually seems plausible based on the evidence, but all the posts seem to be about the low speed going? And wouldn't this also affect water temperature?

2. Condenser not working properly; no obvious damage but at 20+ years old is this likely now?

3. Compressor or gas issue. Least likely I think given how well the aircon works e.g. on the motorway, it's absolutely fine.

So I'm thinking of this course of action:

As Dave recommends above - specifically, could a T4 check confirm the fan operation on all 3 speeds. That way we've either ruled that in or out.

If it's the fan, game on, if not, look to an air con specialist for a gas check, potential replacement of condenser?

[SD1too]

Originally Posted by TomTheTyke

The aircon does blow cold but not when the system is under most load ... fails to cool air when no ram effect i.e. car is in hot weather and not moving.

Hi Tom,

You've established that your 3 speed fan is working on low and medium speeds which rules out a fault with the motor (the fast speed is not triggered by the air conditioning). You've described that proper cooling only results from the forced ram effect of vehicle movement when ambient temperatures are high. This points to an inefficient condenser and/or low refrigerant charge. As you've inspected the condenser I'd say the time has come to book a mobile air con. specialist to check this and correct if necessary.

To answer your other points ...

Originally Posted by TomTheTyke

... all the posts seem to be about the low speed going? And wouldn't this also affect water temperature?

Yes it would.

Originally Posted by TomTheTyke

... gas issue. Least likely I think given how well the aircon works e.g. on the motorway, it's absolutely fine.

I beg to differ Tom. Cruising at motorway speeds provides the best possible cooling to the condenser, much more than the fan can provide at low speed. If the refrigerant charge is below optimum the system will struggle when conditions are at their worst but will appear fine in milder temperatures.

Originally Posted by TomTheTyke

As Dave recommends above - specifically, could a T4 check confirm the fan operation on all 3 speeds. That way we've either ruled that in or out.

The T4 runs the fan at each speed for a fixed time and asks the operator to listen at the front grille. That's no different to the "demist" test and the trinary switch bridging which you've already carried out. There's therefore no point in doing this check.

Originally Posted by TomTheTyke

... look to an air con specialist for a gas check, potential replacement of condenser?

Yes, that's the best way forward Tom.

Simon

[dave lincs]

Hi Tom
I suspect the air con is simply low on gas and needs a garage or air con specialist to check it, As fir the fan Simon is incorrect as under certain circumstances the
Cooling fan will come on at speed 3 , As I suggested before a PM to Big Russ and a trip to see him would soon check fan operation

[Mike Trident]

To give you an idea of just how good the system is in a Rover 75.

When I bought my car the air con didn't work. This turned out to be the resistor, which I changed. The aircon worked well after that.

Later on, after seeing the state of people's condensers on here, I fitted a new one. Boy does my aircon work now!

Even with the high temps we have seen recently my aircon can take the temp down inside the car to what my wife describes as "too cold". I like it quite cool in my car, ive actually seen my wife put her jacket on while I've been driving because she says her arm is going numb lol.

However, my cold car has become the place to be recently, since she started with menopausal "hot flushes"

[SD1too]

Originally Posted by dave lincs

As fir the fan Simon is incorrect as under certain circumstances the
Cooling fan will come on at speed 3 ...

It won't for condenser cooling Dave under any circumstances. See the table on page 56 of the Petrol Engine Management Systems Workbook which shows clearly that the only trigger for speed 3 is a coolant temperature of 112˚C.

Simon

[dave lincs]

Originally Posted by SD1too

It won't for condenser cooling Dave under any circumstances. See the table on page 56 of the Petrol Engine Management Systems Workbook which shows clearly that the only trigger for speed 3 is a coolant temperature of 112˚C.

Simon

It is quite Simple Simon do not belive everything you read from your copy of a Rave disc, Hands on knowledge in my opinion is much better

[COLVERT]

Originally Posted by dave lincs

Hi Tom
I suspect the air con is simply low on gas and needs a garage or air con specialist to check it, As fir the fan Simon is incorrect as under certain circumstances the
Cooling fan will come on at speed 3 , As I suggested before a PM to Big Russ and a trip to see him would soon check fan operation

Could you please elaborate on the certain circumstances you mention ??

How do you check which speed is in actual operation at any moment ??

( Please don't say glue your missus to the radiator grill with super glue to stop her falling off at 70 mph plus.---Lol. )