1978 XJ6L A/C cycling?

I am working on the A/C on a 1978 XJ6L SII, Does the compressor stay on all the time or does it cycle on and off - it kinda creeps me out, also the two electric fans are those meant only for engine temp control or are they meant for the condenser?

Your car has the Delanair Mk II climate control. By design, the compressor will operate in all climate control modes, even when full heating is called for.

Cycling will occur only if the evaporator starts to ice up. The “Ranco thermostat” detects icing and cuts the compressor circuit until temps reach a non-icing level. Evaporator icing depends on several variables and might not occur at all depending on circumstances…so it’s quite possible that you won’t see the compressor cycle.

Cheers
DD

1 Like

okay thank you very much

and for the 2 electric fan in front are those only turned on when engine temp is at a certain temp?

Can’t say for sure. On a Series III XJ6 the fans are activated by coolant temp only. Not sure about a Series II XJ6

Someone here will know

Cheers
DD

I appreciate it thanks!

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Where are the electric fans placed? One or two electric fans were placed in front of the condenser/radiator on AC equipped cars. Exactly why is somewhat unclear - they were not controlled by AC/condenser factors. Though in some applications, usually with one big and one small fan; the small fan were operated when the compressor were engaged…

Originally they were thermostatically controlled by coolant temps - to come on when coolant temps reach 96C. But a PO may have done ‘something’ - check that they operate…

As an aside; it is the thermostat that controls engine temps - the fans just cools the radiator…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)
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Why? Simple; AC equipped cars produce more heat, the flow through the radiator is obstructed and pre-heated a little. With SIII only certain markets had twin fans. Mine only ever went on once. The temp gauge showed more than 100°, but at the fan sensor it sure was about 96. On the V12 the fan comes on with the AC.
The compressor runs full power until the evaporator is at 2°C. Then it switches off until the evaporator is warmer again. Most cars will cycle all the time.

On the USA Series III 6 cylinder cars, at least, the original scheme was two aux e-fans. Later (1982?) this changed to one aux e-fan and an oil cooler.

I’m sure there were good reasons for doing so although sometimes Jaguar rationale is a bit mysterious :slight_smile:

Cheers.

There is two aux fans and they are located near the middle close to the bottom half of the radiator I just cant remember if the fans are positioned On the condenser

the fans are in mid line of the front bumper and are located on the lower part of the condenser and rad, i tested the fans and they come on with power but cant tell if they come on when it gets hot, and the service manual does not give me anything on testing, but i know there is a temp sensor and a relay it goes thru but i have no idea if the relay is bad or not cuz i cant get it out ill try again next weekend

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Are there one or two wires to the temp sensor…?

The relay was used to avoid feedback to the electric system when the fans are windmilling. Other solutions was sometimes used - and POs might also have interfered. Testing the overall function is generally to short (two), or ground (one) wire to trigger the relay. Testing the relay is the common bypass or jumps…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)
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the temp sensor is a one wire, i just replaced that because the car was over heating bad but the gauge kept saying normal temp, i also replaced the temp sensor on the radiator that one is a 2 wire, and i did replace the relay, i did just get a new wiring diagram which i hope works out better but i havent had time and this week its in the 100’s so yah i dont mind burning for 9 hours at work but at home thats a different story

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The dash gauge sensor is ‘one wire’ - and on the water rail. The ‘two wire’ sensor on the radiator is related to the electric fan only.

How did you determine that the engine was overheating? And if coolant level is low; the engine will indeed overheat - but the temp gauge sensor, not immersed in coolant may show fairly normal temps…so…

Frank
xj6 85 Sov Europe (UK/NZ)
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I determined it overheating because of it boiling over, making the fuel vapor lock, and I believe the water pump is not doing it’s job, it could also be a air pocket but after I changed the thermostat it pretty much over heated fast, air pockets take longer to overheat and the electric fan still didn’t come on so I have a new water pump to install and I’m going to flush the coolant system again to see if there is any blockage again so tomorrow after work I got some electrical wires to follow

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Does that simply mean that coolant was ejected at the relief hose, ColdDna…?

Reminding that if the system is fully filled - excess coolant is ejected at the expansion tank vent hose as it heats up and expands, which is normal for the first couple of heat cycles.

If header tank is fitted, the system is filled from scratch at the header tank filler lid with the engine running and the heater fully on. This will ensure that all air is properly flushed - the xj is well ventilated and not normally prone to coolant air locks…

Coolant level is then always checked and adjusted at the expansion tank…

That said; overheating is best checked with an infrared thermometer. The electric fan(s) are usually set to start at 95C - and if the cooling is working properly the electric fans may not start at all…so…?

Frank
xj6 85 Sov Europe (UK/NZ)
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now you say the 2 wire temp sensor is the electric fan one, but on the rail i have two 2 wire sensors i disconnected one of them and the car shut off, and i put the new pump in and its not boiling over and the new temp gauge sensor is reading 3/4 on the temp gauge kinda scares me

On the water rail you should have…

1-Thermotime switch/sensor. Two wires. Forward-most position. Operates the cold start injector

2- Temp gauge sender/sensor. One wire.

3- Coolant temp sensor for the fuel injection system. Two wires. This the one you pulled that made the engine die

4- You might have a fourth sensor in the rearmost position. This sensor, when used, served different functions depending on year and market. But, in any case, it is not related to the electric cooling fans

On the radiator you should have…

1- Sensor/switch for electric cooling fans. Two wires

2- Sensor for coolant level warning light. One wire. (I’m not entirely sure you’ll have this, but you probably do)

Cheers
DD

Understandably.

Under what conditions? Or all the time?

The cooling system is not over-abundant on these cars but you should be able to stay close to the center of the gauge under most conditions. Gridlock traffic in Las Vegas in August? Not so much.

A clogged radiator is always a likely problem. In my experience the best thing is to remove it for professional cleaning at a radiator shop. With DIY flushing you’re never really sure if the clogs are gone.

A weak fan clutch and inoperative electric fans are prime suspects if the problem only occurs at low speeds or in traffic.

A new, correct thermostat is a must just on general principles.

Cheers
DD

the temp gauge is at 3/4 just sitting in my drive way, its not bubbling and hissing anymore or yet, i will just switch the radiator out or get it record my next question is where is the radiator cooling fan relay located at i am preety sure i switched it out with a new one but the wiring diagram i have says there is a Black/red wire going to the radiator thermostat but i don’t. i have a green yellow and green orange