Thread: What does this mean.

Originally Posted by SteveFarmer

This is the infamous and too often encountered "book symbol". It means there is some kind of problem with the HEVAC system

Usually blend motors or it could be a failing RL7 in the fusebox

Commonly called the "Chequebook Symbol" - for reasons that will become obvious later in this song. Another common failure point is the heater core temp sensor. It clips onto one of the heater water pipes and is a bit of a pig to get at.

RL7 = Relay no. RL7 in the front of the fusebox - see under the fusebox lid for relay locations.

Originally Posted by Keithy P38

It was not I who asked the question ;-) relay 7 and I have been good friends for years!

Ooopps I was reading too fast

I recently bought an 80amp relay to go in that spot my reasoning being that an 80amp one will have better heat dissipation than a 40amp

Since the circuit is protected by plenty of fuses I don't think it will cause any problems

I think the main reason RL7 fails is when the blend motors short out and sit there drawing continual current

Steve

Originally Posted by SteveFarmer

I recently bought an 80amp relay to go in that spot my reasoning being that an 80amp one will have better heat dissipation than a 40amp

Since the circuit is protected by plenty of fuses I don't think it will cause any problems

I think the main reason RL7 fails is when the blend motors short out and sit there drawing continual current

here's a pic of the RL7 fuse box location in my old fusebox. I don't think a higher rated relay will help.



I'm not sure why RL7 overheats but I doubt it has anything to do with the blend motors. If it was the blend motor or the blower motor or clogged pollen filters, then why doesn't RL6 also fail. See my pic below, RL6 next to RL7 is fine:



I have a few more pix here: http://www.rangerovers.net/repairdet...l/fusebox.html

I agree with Ron. RL7 is a blower motor relay. I dare say that hot days and high fan speeds (hence high current draw) have a big part to play in the destruction of relays.

Replace your pollen filters and plenum foam. While you have the covers off and the old stuff out, try sucking out debris and dust from the outside and think about (I haven't done this but have thought of it quite a bit) running the AC on low fan and blowing compressed air back in through the cab vents to see what comes out the plenum inlets. Brains trust... Your thoughts and comments on this last bit appreciated before it's tackled. My first lot of cheque book prob's were solved by a thorough clean out and filter/foam replacement. I have it in my head that blend and blower motors get stuck because of debris and then both relay and motorized parts wear out (and jam) due to overworking to distribute AUTO setting cabin air ineffectively. FWIW, the second occurrence of the cheque book for me was resolved by a replacement control unit and fuse box.

Edit: just read Ron's comments. I would trust his input/direction every time. Please feel free to correct
my theories Ron.

Hi

I was originally looking for a metal can relay but these seem impossible to find, so my next idea was an uprated one

My reasoning is that an 80amp relay is designed to handle more current and therefore will be designed to dissipate more heat. It weighs quite a bit more than the 40amp one so it obviously has more metal in it and should dissipate heat more effectively and also not get as hot in the first place.

My other idea was to use a 40amp metal can Air con relay and mount it outside the fusebox but that is a lot more work obviously

Steve

Hi

Just had a look in the ETM and both RL6 and RL7 seem to do a fair bit more than just the HEVAC so I guess it may just be a design faiult where RL7 gets a bit more demand (current) than RL6

In the ETM RL6 gets about 5 mentions whereas RL7 gets about 10 so it is certainly likely to have a higher load.

Steve

Note that there are two RL7 relays. One is in the BECM and you'll see it in the HEVAC section of the ETM. If I recall correctly, it powers the HEVAC panel, the radio, and other stuff.

I recall being caught out by that at one time - until I noticed it was shown in a box labelled BECM.