Blowers won’t work after engine swap!

Hey everyone! I’ve been getting a 1985 jaguar xj6 VDP back on the road and recently put a motor in from another jaguar after mine quit. After getting it back on the road I found out that the blowers would not turn on. When I give the green/white wire on the relay box power the fans blow. I have replaced the relay box, the two fuses in fuse box, and the in-line fuses in the passenger foot well. Before the engine swap the low speed setting never worked and the servos did move from cold to hot while driving every few minutes. After replacing all of the vacuum lines and routing them the correct way they don’t move when the switch is moved. Any help would be appreciated!

Welcome on board, Christian…

Having replaced the relay bank - are you sure you have the connections correct…?

The green/slate (not green/white?) powers the fans directly - bypassing the relays; high speed only. The power input to the relay bank is the brown/white from the 50A fan fuse - internally connected to all 4 relays in the bank. Have you checked for power at that wire.? Due to the high current the fuse box overheats and the connection is lost - check fuse box connection if there is no power.

Loss of low speed may be caused by a faulty relay - and the replacement relay pack may also have faults.

The servo moving arbitrarily between heating and cooling is usually caused by a faulty AC amplifier. With the function switch to ‘Auto’; alternately set the temp control to ‘65’ and ‘85’. With each change, you should hear the servo ‘buzzing’ each and every time. No servo action implies a faulty AC amplifier…

Whenever you turn the function switch out of ‘off’ the compressor should engage - noted by a drop in idle rpms. Does it…?

The electrics AC is sort of intricate - and fixing it may take some time and explanations…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

Welcome to the XJ List!

That is quite an achievement to complete an engine swap. I have done two of them, one in our 1987 XJ6 Vanden Plas in 2014 and more recently one in our 1984 XJ6 Vanden Plas starting in December 2018. I am still fixing a number of small issues in our 1984 XJ6 Vanden Plas that are unrelated to the engine swap but likely due to the car sitting for a few years awaiting a transplant engine. In both cases I used nicely running 4.2L Jaguar XK engines from parts cars that I purchased.

It sounds like you have at least two different A/C faults, including a failed A/C amplifier (very common) and quite possibly a failed replacement relay (there are actually 4 relays inside). Search the Jag-Lovers archives for “A/C amplifier” and you will find lots of posts about A/C amplifier problems and what others have done to resolve them. There is really no way to test the A/C amplifier other than to swap in a known good one. The A/C amplifiers seem to fail quite often. I have a box of 4 or 5 bad ones that either failed on me over the past 19 years in one of our XJ6s or were in one of three parts cars that I purchased. You can find used OEM A/C amplifiers for sale on eBay but often the sellers have no idea if their part is good or bad and no way to test it. One of my bad ones came from an eBay seller, who thought it was good but he did refund my money.

Those relays also fail. I had one fail, and two of the spare ones that I pulled from my parts cars also failed. Did you test the relay before installing it to make sure all 4 relays inside worked? If not I recommend that you remove it and test it to verify that all 4 relays work as they should. If that test doesn’t find a fault then we can look further.

BTW, there have been several recent strings of post from members having a variety of A/C issues. I recommend that you take a look at them to see if these recent and ongoing discussions can help you as well.