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Old 19th May 2016, 06:04   #1
Matt 75
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Default Tepid heater temp

Morning all

My first ever post.

I'm new to 75's but an experienced vehicle technician.

I replaced the cambelt and water pump on my 2005 75 1.8t Connoisseur tourer at the weekend and, when on max temp, the heater isn't getting anything beyond tepid.

So, air lock is the first port of call. Bled the system again, used the bleed screw in the metal pipe above gearbox and still no great improvement.

Top heater pipe gets stinking hot but lower only gets reasonably hot which still suggests air lock or blocked matrix.

Dash temp gauge is bang in the middle and the radiator fan cuts in/out exactly as it should do.

Don't know if the climate system uses the external temp sensor to monitor temps but mine does constantly say 45.5+ degrees outside so know it needs a new sensor.

Anyway, just seeking some advice from those more experienced working on these in case I've missed something obvious.

Thanks in advance

Matt
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Old 19th May 2016, 08:36   #2
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Hi Matt, welcome to the forums, your 1.8 along with all other versions has a useless temp gauge, best place to start is using the on-board diagnostics to obtain accurate data. Dashboard temp gauge sits in middle from circa 75/115 C as standard.

All you need to know about OBD you will find here courtesy of T-Cut
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Old 19th May 2016, 09:26   #3
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The bypass feed to the heater is normally at the same temperature as the top hose. So, I'd say there's insufficient flow through the matrix. Logically, there's a blockage from silt or an air lock in it.

The 1.8 engine more or less bleeds itself, so having done a formal system bleed, I'd be thinking about back-flushing the heater circuit. Heater matrix silting is a very common issue on all models.

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Old 19th May 2016, 09:59   #4
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Check too, the temp sensor has not been tied up close to any heating pipes. It should be facing out in the lower grille on the drivers side.

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Old 19th May 2016, 11:32   #5
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Quote:
Originally Posted by Matt 75 View Post
Bled the system again, used the bleed screw in the metal pipe above gearbox and still no great improvement.
Morning Matt and to the club.

If you didn't follow the official MGR bleeding procedure, try it now. There have been others before you who have found success by this method. Even though you're experienced, try to avoid the temptation of missing out stages because you don't think it matters. I have always followed the (slightly different) MGR procedure exactly for my V6 and have never had an air lock.

Of course, if you didn't have a tepid heater before the engine work, it's unlikely to be a blocked matrix.

Good luck.

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Last edited by SD1too; 19th May 2016 at 11:34..
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Old 21st May 2016, 04:05   #6
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Thanks for all of the responses.

One last question before I decide on my plan of action, does the climate control system utilise the outside temp sensor reading to control the cabin temp?

I only say this as with mine reading 46 deg C min on the dash, even if I set the climate to 27 deg, the air climate will increase fan speed and start to blow lightly chilled air as though it's trying to compensate for it being really hot?

May be barking totally up the wrong tree here but may just be a total coincidence.

Cheers

Matt
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Old 21st May 2016, 09:12   #7
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Quote:
Originally Posted by Matt 75 View Post
... does the climate control system utilise the outside temp sensor reading to control the cabin temp?
According to MGR's climate control diagrams Matt, it doesn't. But you're now considering a fault with the air blending system which isn't consistent with your earlier evidence:
Quote:
Top heater pipe gets stinking hot but lower only gets reasonably hot which still suggests air lock or blocked matrix.
So, did you follow the specific MGR bleeding procedure to the letter?

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Old 21st May 2016, 09:44   #8
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The ambient temperature sensor 'communicates' with both the ECU and the ATC systems. If the ambient signal is incorrect, neither the ATC or engine management will operate as intended. The aircon will run under conditions it would otherwise not be required. For example, if the ambient is below the internal temperature settings, the refrigeration system isn't required. A permanent 45C signal will make the systems 'think' they're operating in the tropics.

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Old 21st May 2016, 11:11   #9
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I've now checked MG Rover's ATC chapter in more detail.
Quote:
Originally Posted by T-Cut View Post
The ambient temperature sensor 'communicates' with both the ECU and the ATC systems.
There is no direct connection from the ambient temperature sensor to the ATC ECU. However, this ECU does have a K-bus connection and the ambient temperature information is available on that (via the IPK). MGR is unspecific about which sensors are involved in temperature regulation and how they are applied.
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I have found something relevant in MGR's 'Petrol Engine Management' workbook. This states that the ambient temperature sensor signal is used by the ECM (in conjunction with the evaporator temperature signal and the trinary switch) to calculate the air conditioning load in order accurately to control the idle speed. There is no mention of the ambient temperature signal being used in connection with cabin temperature regulation.


Quote:
If the ambient signal is incorrect, neither the ATC or engine management will operate as intended. The aircon will run under conditions it would otherwise not be required.
Is this just supposition? RAVE says that if there is a fault with the ambient temperature input (code 12 on the ATC diagnostics) a default value of 10°C is applied.
Quote:
For example, if the ambient is below the internal temperature settings, the refrigeration system isn't required.
Not true I'm afraid. Try it for yourself! Under those conditions the compressor will still run between certain cabin target temperatures, and those are not what you might be imagining! For example, at an ambient temperature of 3.5°C and a cabin temperature of 10.5°C my compressor ran only between target temperature settings of 19 and 22°C.

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Last edited by SD1too; 21st May 2016 at 14:33.. Reason: an addition
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Old 21st May 2016, 13:08   #10
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Not looked any further into yet as injured right hand and can't use it for a week!

Wasn't trying to be awkward, just looking at the evidence it's presenting and evaluating/evolving.

Hoses are getting hot, particularly top heart hose, bottom wasn't quite as hot but the realised I had interior fan on full blast which would cool the return anyway slightly.

Temp gauge fine, rad fan cuts in out fine no evidence of overheating.

Air con fan running all the time even with temps set at 28 deg, only goes off when switch to Eco mode. If lower to 25 deg cooler air is injected into cabin.

This is why I asked about correlation between the sensors. If it does think it's 46.5 deg outside, this may be reason for cool air even at 28 deg setting.

Have run the climate panel self test and no codes stored.

Looked as best I can with bad hand at where outside temp sensor should be and can't seem to find it.

That's as far as I've got so far.

Thanks for all the input so far though, really helpful.

Matt
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