No AC/heater fans

Heater fans1990 XJ-S V 12 Convertible not working: Checked all fuses. Electrical diagram shows inline fuse in Mark III.Does anyone know where this fuse is located. If I can not figure this out, I would like to just hot wire the fans with a switch under the dash. The compressor was removed 10 years ago and no fans for years. Worked great once upon a time…
Sorry I have not been around. Health problems and the new site does not like my computer. Have tried many times but not allowed on. Sometimes it sees me as a new visitor and other times as a member but not allowed on. Thanks to everyone. Harry

Does this help?

Heater fans, Thanks for the schematic and location info… Doug sent that to me earlierearlier. If you look at the schematic where you have the blue arrow, there is an inline fuse (3 amp) just to the upper left of the main fuse panel block. This fuse is inside the dash block for the Delanair unit. How do I find it without removing the complete unit? Thus, the idea to hot wire the fans if I can determine where to find a wire to clip and energize. Harry

It’s not quite as simple as hot wiring the fans, they have a permanent 12v supply and run either by the transistors limiting current flow or by the relays, which are inside the fan housings, switching the neutral to provide full speed running.

The problem could lie in a number of areas depending upon who has tinkered with it in the past. Be aware also that even when the fans are running, without the A/C operating the system will revert to re-circulating rather then fresh air, although with a convertible that may not be the problem it is with a coupe.

My ‘89 has the same problem. Fans where intermittent for a year, then stopped. Also had obvious heater core leak, getting worse during that time. Found a post that pointed to the fan relays behind driver ( left hand) inner kick panel.
As described in that post, my heater core leaked directly on these relays, corroded them.
About ready to tackle this

On its way to the stereo!

The fan relays are a single unit containing four relays. If they cause any grief, you can replace them with four individual generic relays.

The diagram says the fuse was deleted at VIN 156989. You probably don’t have it.


Thanks, Doug.

You have really been a guide for me and others with your constant comments and reports to the group. Now I only have to wait for the rains to stop and warmth of Spring to get the fans working. I have given up for the winter. Surely, someone has had the same problem outside of the fuzes and computer that made it easy.

Best, Harry


Thanks. I consider you the real William Lyons. You have helped in the past many times.

I have changed the relays, no luck. No leaking water. The loss is somewhere in the depths of British bird nests. Since both fans are not working, it has to be somewhere internal to the III but I am too old and not double jointed to remove the complete system. Somewhere, someone has had a similar problem and found an answer.

This is the same car that would not start 5 years back. Changed everything after the front pulley fell off on a road trip. The old guard of Jag Lovers all chipped in to help. No luck. Then, a year or so later it just started and has run ever since.

Thanks for your personal attention. I have the Jag in my will to go to you as you do need a road queen. You almost got it 2 years back. I trust my distant family carries out my wishes.

Best, Harry

This is a MkIII, isn’t it? The fans are controlled by the infamous Darlington transistor. Entirely plausible that both have failed.

Thanks for the email Kirbert,
I have your book, and remember reading about coolant leak causing the fan issue. That was years ago and then saw the post on the forum. I signed up years ago, donated I think , but couldn’t find user and password.
So had to make new account.
Last time I was on forum was asking opinions on my XJS injectors and running E85 fuel. Actually ran a few hundred miles on alcohol. No troubles except with finding E85
Great work. Thanks again
Brandt (Corky)

Should still work on high, shouldn’t they? Relay bypasses the transistor when on high, if I recall.

Thanks for the research….I thought I had seen everything in archives but somehow missed this one. Darlingtons…!


Since I have new ideas for a cure, I might dive into the fan project this weekend and not wait for warm weather. It would be nice to drive some in cooler temperatures. Thanks to everyone.