How to test heat pump
 

Can some kind soul explain how I can test the heat pump in my 2005 XK8?

Thanks in advance!

Jump the relay
 

Stamford,

Been there done that. In the front engine fuse box compartment, there’s a relay which you jump.

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The heater pump under the car should “whir” but the trouble is that it’s got a magnetic clutch which is known to fail. So pump motor spins but doesn’t pump. The way I checked this was to take one of the bulkhead hoses to the heater core off and physically checked I had flow.


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Pic of location of bulkhead hose connectors for heater core. The other thing to note is that if you have no heat it’s often the water solenoid valve thingy.

Good luck

Thanks, David. Much obliged.

At the relay position, you can check for continuity. "Infinity" likely means the brushes no longer make contact and the pump has to be removed for a rebuild or replacement ($$). If there is continuity, you can bring a power wire and check that it spins. It is fairly quiet, but can be heard clearly with the engine off. As already pointed out, the motor spins a magnet, with the hope of spinning the impeller, but it is hard to confirm.

If you have no heat, another suspect is the heater valve next to the pump. Easiest is to disconnect it as it defaults open. Be ready for a lot of heat in the cabin after that. The connector is on the firewall, sort of on top of the valve. Pump connector is next to it. Easy to access.

If still no heat after the pump is OK and the valve is unplugged, try and do a heater core flush. The core pipes are right there and easy to work once the expansion tank is out of the way. Get proper hose extensions (I did clear tubing from the home store, 5/8?) and a garden hose adapter. Flush in both directions. Use a chemical cleaner for the recommended time and flush again. This brought heat back for me.

Problem is, pump and valve are $$ and sort of hard to diagnose individually.

Best of luck, keep us posted.

Thanks for the info!