MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGF Technical - aircon functions only after 5 minutes

Hi all,

I would like to ask you the following, a friend of mine is considering buying an MGF with aircon, but the aircon only starts to blow in cold air after 5 minutes and the fan on full swing 3 or 4. When he switches to 1 or 2 warm air flows in even with the control on cold air. The dealer says this is normal, anyone having the same experience, or is the dealer talking crap.

Thanks for any reply,

Marten
Marten van der Velde

Definitely not normal - air con should be come on and blow cold very quickly. The time I really notice it is on damp winter mornings. It clears the screen in about a minute.

The air con will not work if the fan is off, the temperature near freezing (unlikely in the last few months!) or the engine in running hard and hot.

Good luck

Patrick
Patrick Beet

Marten

What you are describing is exactly what happens on my car, except I DO NOT have air con, just the standard blower. I would also add that even on setting 3 or 4 I never get cold air, certainly cooler but hardly cold!

Dealer has told me this is normal due to ancient design of heater matrix.
Billy Bob

Valve for the heater matrix is local to the matrix, in other words inside the dash. This means that the flow pipework from the engine to the matrix (which runs inside the transmission tunnel) is constantly full of hot water, acting like a radiator in the middle of the car.

The best you'll get from the air vents in a non-aircon F/TF is air the same temperature as the pickup point (the grille by the windscreen wipers), therefore, 'cold' is actually 'ambient' and 'hot' is related to engine temperature.

The design of the matrix is ancient, being effectively a small radiator sited within a fan assisted air duct. However this does not make it a bad piece of design, indeed within it's perameters it works very well - if it ain't broke...

However, if it IS broken, then it is a right pain in the *rse to replace, needing not only a drain down of the cooling system, but also the entire dash removed from the car. At a guess i would say it's around a 2 day job and this is probably the main reason behind your dealership's comments Billy Bob.

The valve on the matrix is a manual item, connected to a wire attached to the back of the heater control, as is the vent selector dial, the only electrical part of it is the fan speed (which is on a multiplug behind the fascia).

If you are getting warm/hot air when the dial says cold then it is possible the cable/wire to the valve isn't fitted properly (may be twisted) meaning that when the dial is set to cold, the valve is only partially closed. The alternative is there MAY be a fault with the valve in the matrix, if this isn't closing fully then there will still be some circulation of (hot) coolant through the matrix and this will radiate some heat into the airstream from the vents, producing the symptoms you describe.

There are pix of the heater control unit and the cabling behind on the SOS site, unfortunately there aren't any good pix of the heater unit as i never stripped Scarlet's one out. Usual URL >> http://www.sfforever.co.uk <<, click on REBUILD and then select the DASH PART 2 gallery.

HTH

SF
Scarlet Fever

Agree with everything Andy said, except

>This means that the flow pipework from the engine to
>the matrix (which runs inside the transmission tunnel)
>is constantly full of hot water, acting like a radiator
>in the middle of the car.

Is not true if the heater is turned to cold, there should be no water flow thru the pipework in this case.

>The design of the matrix is ancient, being effectively
>a small radiator sited within a fan assisted air duct.

the alternate design is to keep the radiator hot at all times and to route the air diffrently, this is no more 'modern', although it does give finer control it is more bulky.

Your heater is broken, it might be as little as a cable being loose, but it is no doubt broken.
Will Munns

Marten,

I would also make sure that the airco system is properly charged with the right amount of R134a coolant. This is something often overlooked by dealers because they don't have the right airco servicing equipment. All airco equiped cars naturally loose a bit of the coolant with time and it must be checked and topped up every year. Every 3 or 4 years you must also replace the "dehydrator" (not sure about the correct name of that thing in English...).

My car has airco and it blows cold air after 30 seconds with fan only on 1, so that dealer you mentioned is talking bullsh*t!

Per
Per

>> Is not true if the heater is turned to cold, there should be no water flow thru the pipework in this case. <<

The control for this Will is at the matrix end of the pipework, this means that there is an open pipe straight from the engine full of hot water (regardless of the dial position or whether there is any flow in the pipe) inside the cabin.

The water is stagnant in the pipe until the matrix valve is open, but it is hot at all times because there isn't a valve at the engine end of the pipe.

SF
Scarlet Fever

>this means that there is an
narrow, long
>open pipe straight from the engine full of
rapidly cooling
>hot water

at the engine end there will be some conduction, but by the time the pipe reaches the footwell it should be quite cool
Will Munns

Hello,

Thanks guys for your comments, I thougt there was something wrong as I could not believe an aircon working after 5 minutes.
So the dealer should sort it out before the car will be bought.

Thanks again for all your advices and comments at least my friend will not be cheaten by a MG dealer.

Thanks,

Marten
marten

Meant to time it this morning but forgot. However the cold air was coming out of the vents after driving 70 yards (or metres!) so suspect we are talking 20 to 30 seconds.

Cheers

Patrick
Patrick Beet

>> but by the time the pipe reaches the footwell it should be quite cool <<

Should be yes, but in reality? Certainly it is still hot under the ashtray, hence the recent threads about warm ashtrays and transmission tunnels.

>> http://www.sfforever.co.uk/viewgallerypicture.asp?id=19-24-64-65-66-67-68-69-70-71-72-73-74-75-76-77-78-79-80-81-82-83-84-85-86-87&queryon=15 <<

This picture was taken in response to one of these threads. When the thread appeared i didn't put too much faith in it, but have since done some investigating and after a reasonable run (say 10-15 miles) the flow pipe is very warm right up to the heater matrix and it is only the valve on the matrix that prevents this heat getting into the air vent system.

SF
Scarlet Fever

Scarlet, Both pipes or one pipe? If it is conduction then both pipes should be hot, if it is a not fully closing valve then only one pipe should be hot.
Will Munns

Sorry, both pipes were hot, I had the cubby box out of the transmission tunnel and they were hot under here and very warm behind the triangular footwell panel on the driver's side where the pipes enter the heater unit.

SF
Scarlet Fever

OK, that showed me ;-) surprised that it conducts that far, are the pipes rubber all the way?
Will Munns

Nope, they are metal in the transmission tunnel. There are 2 gear selector cables and 2 metal heater pipes inside the tunnel, the gear cables are rubberised, the heater pipes are tucked away inside the metalwork of the tunnel, all four look identical, but they feel very different. At the dash end they become rubber and there are a pair of metal L shaped tubes coming out of the matrix (which the rubber pipes connect to).

IIRC the pipes are rubber coming out of the engine, so i assume they connect to the metal pipes somewhere under the petrol tank (rather worringly!) :-)

SF
Scarlet Fever

Timed it this morning. 15 seconds from start of engine to cool air out of vents!
Patrick Beet

This thread was discussed between 15/09/2003 and 18/09/2003

MG MGF Technical index

This thread is from the archives. Join the live MG MGF Technical BBS now