I have a 1993 Volvo 960 wagon (147K miles, awesome vehicle). The leather seat on the passenger side does not heat correctly. I have tried the normal checks:

Seat heater pad circuit is unbroken (pulled and checked connectivity with voltmeter)
Back heater pad circuit is unbroken (pulled and checked connectivity with voltmeter)
Switch (with light) works (checked for power with voltmeter)
Relay under seat turns on.... but then turns off(?)

I checked the voltage at the seat pad to confirm that power was getting to the pad (meaning it went through the switch). I am getting power, but only for 5 seconds.

I checked that I was getting power past the relay and I came to a surprising problem.

The relay under the seat will click (I hold it in my hand to feel the click) and allow power through to the heating pads, then after about 5 seconds, it will click and cut power to the pads. After ~30 second delay, the relay will click again, allow power again, but then click after 5 seconds and cut power.

Thus the seat is only getting 5 seconds of power every 35 seconds, and does not heat.

Does anybody know what the problem is?

Because this is the leather version there is not a thermostat in-line with the pads, so I don't think that is the problem.

 

May be the relay is faulty? I'd start there.

 

Thank you for the suggestion. I'll try swapping the "good" relay from the driver's side and the one on the passenger's side this evening and report back.

Would photos help? I could even take a video to show the cycling of the relay.

 

it's working fine. The relay won't stay on unless it's COLD. If you want to test it further, let it sit in the freezer for a while.