Rapid clicking noise and then A/C cuts out
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From: Half Moon Bay, CA
Rapid clicking noise and then A/C cuts out
Was driving my 1990 XJ6 4.0 (aka XJ40) Vanden Plas yesterday with the AC on and all is good - -air is cold and suddenly there's a VERY rapid clicking sound behind the dashboard and the cold air stops. Fans still run, but no cold air. Stopping and restarting the car and/or fans makes no difference. Any ideas what's going on?
Joined: Feb 2014
Posts: 20,512
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From: Crossroads of America
Hi wmlaven,
That's a curious set of symptoms.
A couple of questions first:
1. Do the fans run on all speeds or only on high?
2. What area of the dash did the rapid clicking sound come from? Left, Right, Center?
3. Could the clicking sound have been arcing (electrical sparks)?
One suspect might be the A/C and Radio Relay, which could make a rapid clicking sound just before it failed. I'm not sure if the fans will cease to operate if this relay fails: a quick test would be to see if the radio will come on. The relay is mounted on a panel behind the glove box. Could the sound have come from that area?
Another suspect might be the A/C compressor clutch relay, but it is mounted on the right radiator support, so I'm not sure you could have heard it fail. With the engine running and the A/C on, watch and listen to the clutch to see if it engages and disengages. If not, that doesn't necessarily mean the relay has failed, but something in the clutch control circuitry is malfunctioning.
The climate control microprocessor is mounted on the right side of the center console behind the footwell trim panel. It could have developed a problem, but I don't think the fans would run at all without the CCM operable.
Some of the vents are vacuum controlled, but I don't think a vacuum leak would prevent cold air from exiting at least some of the vents - especially the vents in the rear seat center console.
Another thought is that the system is designed with two blower fans, left and right. The fans draw air from either the outside, via an opening in the firewall under the windshield cowl, or from the passenger compartment when Recirculation is selected. The fans blow air toward the center console, where their two airstreams collide and increase the pressure in the ducts and therefore the velocity of the air that exits the vents. If one of the fans fails (very common), you will still hear fan noise, but the velocity of the air coming from the vents decreases dramatically. Is it possible that only one fan is running? You can check by pulling the fuse for each blower motor - if the fan noise doesn't change when you pull one of the fuses, that blower fan motor has failed.
You can download the Dealer Training Manual for the HVAC system here:
Jaguar Delanair Mk. IV Climate Control System Dealer Training Manual
I'm also attaching another document that explains the design of the system. I hope these documents will be helpful, and that other members will have some better ideas.
Cheers,
Don
That's a curious set of symptoms.
A couple of questions first:
1. Do the fans run on all speeds or only on high?
2. What area of the dash did the rapid clicking sound come from? Left, Right, Center?
3. Could the clicking sound have been arcing (electrical sparks)?
One suspect might be the A/C and Radio Relay, which could make a rapid clicking sound just before it failed. I'm not sure if the fans will cease to operate if this relay fails: a quick test would be to see if the radio will come on. The relay is mounted on a panel behind the glove box. Could the sound have come from that area?
Another suspect might be the A/C compressor clutch relay, but it is mounted on the right radiator support, so I'm not sure you could have heard it fail. With the engine running and the A/C on, watch and listen to the clutch to see if it engages and disengages. If not, that doesn't necessarily mean the relay has failed, but something in the clutch control circuitry is malfunctioning.
The climate control microprocessor is mounted on the right side of the center console behind the footwell trim panel. It could have developed a problem, but I don't think the fans would run at all without the CCM operable.
Some of the vents are vacuum controlled, but I don't think a vacuum leak would prevent cold air from exiting at least some of the vents - especially the vents in the rear seat center console.
Another thought is that the system is designed with two blower fans, left and right. The fans draw air from either the outside, via an opening in the firewall under the windshield cowl, or from the passenger compartment when Recirculation is selected. The fans blow air toward the center console, where their two airstreams collide and increase the pressure in the ducts and therefore the velocity of the air that exits the vents. If one of the fans fails (very common), you will still hear fan noise, but the velocity of the air coming from the vents decreases dramatically. Is it possible that only one fan is running? You can check by pulling the fuse for each blower motor - if the fan noise doesn't change when you pull one of the fuses, that blower fan motor has failed.
You can download the Dealer Training Manual for the HVAC system here:
Jaguar Delanair Mk. IV Climate Control System Dealer Training Manual
I'm also attaching another document that explains the design of the system. I hope these documents will be helpful, and that other members will have some better ideas.
Cheers,
Don
Last edited by Don B; Dec 1, 2017 at 07:52 PM.
Thread Starter
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Member
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From: Half Moon Bay, CA
1) Fans run on all speeds.
2) Clicking behind speedometer.
3) No arcing, it's a motor chattering.
On another forum several said it's probably the blend flap motor sticking and sent pics and descriptions that fit the bill. Sound right to you?
2) Clicking behind speedometer.
3) No arcing, it's a motor chattering.
On another forum several said it's probably the blend flap motor sticking and sent pics and descriptions that fit the bill. Sound right to you?
Joined: Feb 2014
Posts: 20,512
Likes: 15,284
From: Crossroads of America
A vacuum solenoid leaking or failing could sound like a motor chattering, but I'm still not certain that failure of one could prevent any cold air from passing through at least some of the vents.
Is it possible cold air is coming from the floor vents but not the dash vents?
Have you tried switching to heat to see if hot air will come from the vents?
Cheers,
Don
Last edited by Don B; Dec 3, 2017 at 01:56 PM.
Thread Starter
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Member
Joined: Apr 2017
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From: Half Moon Bay, CA
It's hard to pinpoint exactly where the noise is coming from.
Cold air doesn't enter anywhere.
On heat, it doesn't seem to allow hot air in either.
However, I just drove an hour on the hwy. and with the fans OFF, warm air enetered the windshield vents strongly and seemed to be wafting in at least the side vent and maybe the center vents, too. The thermostat, BTW, was on cool (again, fans off).
Cold air doesn't enter anywhere.
On heat, it doesn't seem to allow hot air in either.
However, I just drove an hour on the hwy. and with the fans OFF, warm air enetered the windshield vents strongly and seemed to be wafting in at least the side vent and maybe the center vents, too. The thermostat, BTW, was on cool (again, fans off).