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Before this morning, heat and blowers have worked mostly as expected - when switched to hot (75 - 85) hot air would blow out of side dash vents and leg vent. This morning it initially did that, but mid-drive all vents except defrost started blowing (so legs, dash sides, and middle), and cold ambient air came out of the vents regardless of the temp setting. So my guess is it's no longer diverting air properly - wrong doors are open, and/or air is not getting pushed over the heater core.
My understanding is that the dash switch signals the AMPLIFIER, which sends power to the SERVO. There is also the HEATER VALVE which could be stuck closed? Other than checking vacuum, any guides to troubleshooting these components, or is it trial by replacement?
Two Additional notes:
1) I'm not sure that the "Low" setting has ever worked since I've had the car.
2) Cooling does not work, I haven't really even looked at the compressor
What year model ??
If a Series 3 XJ-6, start with the heater valve. Have someone turn the Temp control from 65 to 85 and viceversa (with engine running) while you watch the valve mechanism open and close up and down.
if the Vents were working fine, I doubt it is the Servo.
A vacuum leak can cause the system to revert to the Defrost / Screen vents only.
The Amplifier can also be the cause. They do fail.
Contact Gary at www.jag-aire.com for expert help.
Hmmm…it started working again this afternoon. May have to wait this one out.
Edit: ok, stopped working again. Valve seems to be moving fine- when I unplug vacuum line it rises, plugged in it drops. So I think I’m looking elsewhere…
Ok, heater valve moves when vacuum is applied and removed. The issue seems to be that turning the control knob does affect the vaccum to the valve. Where does the vacuum line to the heater valve come from? I’m trying to get a sense for order of operations here so I can trace backwards.
Where does the vacuum line to the heater valve come from?
Vacuum to the heater valve comes from a vacuum switch on the servo. Vacuum is sent to the valve in cooling mode only (to close the valve).
This morning it initially did that, but mid-drive all vents except defrost started blowing (so legs, dash sides, and middle), and cold ambient air came out of the vents regardless of the temp setting. So my guess is it's no longer diverting air properly - wrong doors are open, and/or air is not getting pushed over the heater core.
Right.
Is this change is accompanied by the whirring of the servo? The servo operates as commanded by the amplifier. The amplifier is the brains of the system. You might have a failing amplifier...giving the servo erroneous commands. But....inputs to the amplifier could be wonky as well. This would naturally result in the amplifier giving weird commands which are dutifully obeyed by the servo.
If this change in operation happens with no whirring from the servo then I'd look for vacuum problem.
Thank you!
I seem to be getting consistent vacuum to the heater valve, so seems like something is stuck in cooling mode. Does that sound right? Either amplifier or servo could be at fault I suppose...thermostat I suppose could be an issue as well. I'm not hearing whirring, although with the fans blowing I perhaps could miss it. Probably check fuses next, then maybe look at the amp and servo and see if there's anything obvious.
and if no whirring, it could be a bad servo, or a bad amplifier not talking to the servo, right?
Right.
Or bad connections!
Amps often fail in weird ways, and fail much more often than servos. Unfortunately the only way to tell if it (the amp) is failing is to replace it.
If all the things you can check are OK, replacing the amp usually fixes the problem. But they're not cheap....so it's a bit of a take-a-gulp-and-go-for-it situation
Amps often fail in weird ways, and fail much more often than servos. Unfortunately the only way to tell if it (the amp) is failing is to replace it.
If all the things you can check are OK, replacing the amp usually fixes the problem. But they're not cheap....so it's a bit of a take-a-gulp-and-go-for-it situation
Cheers
DD
Haha- fair enough!
Is there a dashboard thermostat? How does it play into the equation? For example, if it’s 40 degrees Fahrenheit out, would the thermostat stop the servo from sending vacuum to the heater valve so heat stays on, even if dash controls are set to 65 degrees?
There are two temperature sensors - one in the car which is under the crash roll on the dashboard (above the coin tray). The other is external to measure ambient temperature. So if it is particularly cold outside, the system will bias more towards heating, and vice versa
If you conclude that your amplifier is at fault, I have just finished testing of a replacement amp design that I have built. The control circuitry is the same as the original Delanair one but the relays are replaced with a solid state motor controller chip.
I am able to provide one of these for a much more affordable price than the current alternatives on the market. I do not have a source of the connector plugs, so the original plug needs to be spliced into the flying leads or soldered onto the board. My version of the amp has an optional set of 3 LEDs which can be fitted into the ashtray and indicate amp functions.
PM me if you are interested in obtaining one. I have 3 built and tested in stock.
Thank you for sharing! It was back to working today…I know the car hadn’t been driven in some time before I got it, so will see if “blowing out the cobwebs” gives a consistent fix. If not, I’ll plan to hit you up.
There are two temperature sensors - one in the car which is under the crash roll on the dashboard (above the coin tray). The other is external to measure ambient temperature. So if it is particularly cold outside, the system will bias more towards heating, and vice versa
If you conclude that your amplifier is at fault, I have just finished testing of a replacement amp design that I have built. The control circuitry is the same as the original Delanair one but the relays are replaced with a solid state motor controller chip.
I am able to provide one of these for a much more affordable price than the current alternatives on the market. I do not have a source of the connector plugs, so the original plug needs to be spliced into the flying leads or soldered onto the board. My version of the amp has an optional set of 3 LEDs which can be fitted into the ashtray and indicate amp functions.
PM me if you are interested in obtaining one. I have 3 built and tested in stock.
Update here: I purchased the Amplifier unit from @Andy T. and installed it this afternoon. Heat seems to be working great now! Easy install (small wires can be annoying, but no difficulty other than putting those together), and the LED indicators are brilliant, and give me confidence that the unit is functioning as it should be.
Thanks, Andy - for an amazing contribution to the community!
10-10-2023, 10:59 AM
Blower with no heat issue (xj6 siii)
