Best place to start is checking the 4 system fuses: #10 and #11 in the main (LH) fuse box, #5 in the aux (RH) fuse box, and the inline fuse which, as I recall, is near the RH side of the main a/c case, behind the RH console 'cheek panel'.

The servo motors are very quiet so you might not hear them over the fans. Might be easier to hear/see operation of you remove both cheek panels.

Cheers
DD

 

l would start testing at the vacuum system. Start at manifold and just check each line in turn. If you don't have vacuum you will not have a/c flap control and heater valve will be stuck open. The a/c vacuum solonoids are easy enough to get to in order to check them and their vac lines.

 

 

Does the compressor engage ?

 

 

OK, just a minute. Before you can start fixing it, we need to define what the problem is.

Question 1 : Do you get air flow when you set the fan speed switch not to zero?

The way it's supposed to work is that the A/C compressor is always on, IF the fan speed is not set to zero. This might seem wasteful because the A/C compressor is on even on a cold morning when you have full heat. That's the way it is.

Question 2 : on the temp knob, can you pull it out? If so, you have Delaniar Mk III. If the temp knob has no feature where it pulls out, you have Delaniar Mk II.

On the Delanair Mk III, pulling out the temp knob overrides cabin temp control using feedback from the cabin temp sensor, and just sets the air temp.

So try this : Fan on medium, pull out left hand knob. With the engine warm, vary the set temp. The air temp and direction should vary.

My understanding is that when you have the fans running, AND you vary the temperature, there is no response - to either the direction of air flow, or to the temperature. Is that correct? If so, forget about vacuum for now, as the servo motor is electric.

 

The climate control system is 'on' unless the mode control knob is turned to 'off'.

The compressor operates in all modes: heating, cooling, blending, defrost. Thus, no separate A/C button

In your case I'd say the compressor is not engaging as the engagement click is quite distinct....and you're not hearing it. Confirmation would be visual: the pulley is always turned by the drive belt, obviously, but when the clutch engages you'll see the outer section of the pulley spinning as well.

Pulling the temp knob out gives manual hotter-colder temp control. Pushing the knob in reverts to automatic temperature control.

Cheers
DD

 

Just read the bit about the fans only working on high speed. Major clue this. This means that the climate control is being inhibited for some reason. As far as I know, there are 3 possible reasons for this :

1) The heater core is not getting hot. Bizzarely, the entire climate control system is inhibited when the heater core is not hot, including A/C, except that an override is allowed for high fan speed to give some defrost. There's a thermo switch on the hot water line.

2) No power to the climate control amplifier.

3) Blown climate control amplifier.

You're wasting your time messing with vacuum, and the A/C compressor. You need to get the other fan speeds working, then proceed.

 

Not exactly. In cooling mode the input from the coolant temp switch is bypassed. In other words, if you're asking for cold air the system does not wait for the coolant temperature to reach xxx-level. Of course the system has to recognize that cooling is being asked for. And, as you say, it is bypassed in defrost mode as well....and defrost mode always defaults to highest fan speed.

This feature is designed to prevent getting blasted with cold air when the system is in heating mode. when the coolant get warm enough to actually provide cabin heat the switch lets the system turn out.

As a test the switch is easily bypassed. Some leave it bypassed, in fact. Just join the two wires together

I agree. Get the control system fundamentally operational and proceed from there.

Cheers
DD

 

An 88 should be Mk III. But it's possible it was built before the cutoff, and has Mk II.

 

 

The default mode for the heater valve is open, so heat is always the fallback. It takes vacuum to close it That being said, it's worth a check of the right side intake manifold to see if the vacuum pipe is actually connected to the maniolfd. It's a small pipe, on my 94 it's maybe 1/8" dia plastic line.

For the fans, they bypass the control system on high and get 12V directly from a relay. For the lower speeds, they are controlled steplessly by a darlington transistor on a printed circuit in the blower fan housing. Those transistors are known to fail, so that will cause the motor to not run when anything less than high is called for. If you're handy with electronics, it's not that difficult to replace the transistor and rebuild the board. I'm pretty sure the circuit diagram and step by step photos are either here or on Jag-lovers.

 

 

Here's some info:

Air conditioning blower control

I did this job and removing the blower was probably the most difficult job I've ever done on a Jag, personally. But experiences vary.

Cheers
DD

 

 

 

All that is really required is changing the fill ports and then filling it up. However, you obviously have a leak, so you need to find the leak first. A common suspect is the retaining plate on the compressor that holds the hoses on. It's really a bit thin, and bends a bit when tightened by the bolt in the middle and doesn't hold the hoses square to the compressor.

At this age, it can be many things. I just fixed the AC on an 81 XJ12 and it ended up being two tiny corrosion pinholes in the condensor that I had to braze up. That after I went through and changed the O rings in every joint, changed the compressor and the receiver dryer. It had been apart before, and whoever put it together didn't know what they were doing and put in wrong sized O rings.

To do AC right, you need all the tools: vacuum pump, full gauge set and hoses, can tap and thermometer. Also patience and thoroughness.

My leak finding procedure is I have a hydrocarbon detector good to 5 PPM, and I have made an adapter so I can use my BBQ propane bottle to connect to the gauge set. I vacuum the system, give it about 5 psi of propane and then go over each joint with the detector. It works quite well to find leaks.

 

 

Earlier cars had a superheat switch, later ones had a pressure switch. If the freon pressure was low the pressure switch would prevent the clutch from engaging to preserve the compressor. The superheat switch melted if the freon temperature got high from low freon. It doesn't work as well as a pressure switch and has to be replaced if it trips. A pressure switch doesn't need to be replaced. If a compressor fails and seizes, then there are bits of metal spread throughout the entire AC system. Basically you have to replace everything the freon touched at that point. A very major and expensive job.