I am not getting any heat with defroster selected and temp set to high.

With A/C set to 78, it will freeze you out.

My thought is heater valve or heater pump. I checked 10A fuse #15 in the front fuse box left side under the bonnet(hood). Both the pump and valve share a ground EM8R that Fig. 07.2 in 99 XJ Series Electrical Guide says is a two wire eyelet pair at the EMS L/H Bulkhead Stud.

Anyone know where that ground stud is located?

Any other suggestions?

 

No need to find the stud itself. The electrical plugs (2 pin) are on the bulkhead on the L/H side of the car (looking from the driver's seat). The heater one is black, and the valve one is white.

 

It's almost certainly the heater pump brushes worn down although blocked heater coils have been known. 3/4hr job to install a new/replacement pump.

Whilst doing it, if you can get the hoses off the heater coil inlet/outlet, give them a backflush - the return pipe is the one nearest the wing ---------------->



Note the diagram is drawn as if looking through the bulkhead.

 

The connectors for the valve and the pump are located differently on my 99. I disconnected and cleaned both connectors with contact cleaner. I checked fuse and also the relay. On LH drive cars the relay is in the front of the two fues boxes on the left side of the engine bay. With the cover removed, there are several relays forming a "t". The heater relay is the rear most of the three relays forming the top of the T. I seem to recall that there is a problem with the brown relays burning contacts and Jag issuing a bulletin about using black relays as replacements. Mine is brown, so I removed the cover and had the Mrs turn on the defroster and turn it off. Relay works, I will check the contacts for signs of burning. With the relay cover removed, the copper plate on the left of the photo moves when the relay is activated.

While checking the relay operation, I listened to the Heater Valve and the Heater Pump with a stethoscope. Neither had any sound.

I could not find a data plate on the pump, but the valve had a Denso data plate with the P/N MNA 6711AC

Jim Forrest may be right about the pump motor brushes.

I am going to see if I can find replacements for both the valve and the pump.

 

It's unlikely to be the solenoid - its default condition is 'no power' and set to pass water through the matrix. The only time it moves is when no heat is called for. I drew this diagram when I was working the circuit out some time back ----->

 

By the way - you can easily fit new brushes but identical units (with braided tails) are impossible to find. To get round it just get the brushes off eBay and solder the old tails onto the brush-holder. The power will go through the holder and spring ok. The brushes are 12mm long x 5 x 5.

You'll need an impact driver (undriver?) to get the casing screws out, and the armeture won't lift out completely because of the bearing. If you pull the bearing off make sure you measure its position on the shaft as it doesn't sit against a shoulder. Get it wrong and the armeture will be jammed.

Install the brushes by snipping off the tails at the (old) brush end - and solder them to the brass holders - then prise open the 'flaps' at the end of the holders, pull the spring out, insert the brush and then put the spring back.

 

I agree that the carbon brushes are the likely problem. I found similar sized brushes at my local hardware store...they were replacement brushes for electric tools. I replaced all my heater hoses and checked the heater valve and pump at the same time. One of my brushes was paper thin...the other barely making contact. Now..the heater works great !

 

Hopefully its just the heater pump. Don't forget the heater core as a possibility, these can clog up, specially if wrong coolant was used and mixed. You can unclog them if you have access shop air and a blow gun.

 

Just to chime in - if you have a replacement pump sourced, you can actually get the old out and new in, in 10-15 minutes. Once you get a good look of it, you can actually get enough flex in the hoses without stretching anything to the point of breaking, and wiggle things out. I ended up doing the same last winter (or was it the one before..), when mine died. I pulled the old out, saw the brushes were bad. Put it back in so I had a complete coolant loop until the new arrived, and then swapped them in the driveway in about ten minutes. I might have posted it somewhere, but it's certainly not an awful undertaking, and is really a likely culprit from what your symptoms sound like.