After taking several years to find the tiny a/c leak in my system, I thought maybe the a/c-heat system was all set. But not in this *!&#!+#! car, oh no.
I know that the amp appears to be bad–will only go to cooling. Have removed it completely and manually driven the system to full heat. All outlets are open/closed as they should be. Two problems:
Sometimes the air coming from the footwells is quite cool, while dash vents are warm. Sometimes both upper and lower are warm. Frequently goes from (maybe ) warm to cool while driving, but never had it go from cool to warm. If it’s warm, it started out that way.
Have had good HOT air once, but generally it’s just warm. Temp gauge reads just under 90.
Water valve is fully open, hoses hot both sides. Looking into both sides of transmission tunnel all vac hoses appear to be connected. Pretty sure a month or so ago, I checked if vacuum held from firewall back, and it did. (Have been thinking about problem since–and obviously getting nowhere. )
I’m suspicious this may be a (sporadic?) vacuum problem but if so, could use some advice on how to track it down. Or other ideas.
Thanks!
Thon
'87 XJ6
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With manual control set to full heat, the system should stay in full heat, Thon…
In which case, the dash vents should stay closed - they are opened by vacuum when the servo resets to ‘cooling/maintain’. Are you sure the servo is set to ‘full hot’ position - and how have you verified this? Including your control over the servo; have you tried altering servo positions - ensuring that the servo does move…?
Have you tried the ‘def’ setting? It partially bypasses the AC amp control; the defrost vents should open (held closed by vacuum in other switch positions). All the above sort of verifies that vacuum is available and under some control…
The open face vents are suspicious - as said; they should be closed in servo ‘full heat’…
That said; the standard vacuum leak test is to connect a vacuum gauge to the hose at the vacuum reservoir - then run the engine, gauge should read idle vacuum. With the engine running, clamp the vacuum hose below the AC one-way valve - the vacuum gauge should remain stable; drop in vacuum indicates an inside leak.
Then; remove that clamp and place on the hose going into the cabin from the ‘T’ connection above the one way valve - and shut down the engine. Again, the gauge should be stable - if it drops; the one-way valve is leaking…
Heat generation depends on coolant temps and heater matrix efficiency. In addition, as ambient air is used during heating; cold outside air will influence air vent temps - though in principle, the heater capacity should be ample to deliver fairly hot air to the inside even in a cold climate…
As an aside; have you made any attempt to verify AC amp function - some faults, possibly implied by the testing in ‘manual’ may cause an apparent AC amp malfunction?
The basic AC amp test is to verify that the amp moves when the temp setting is altered…
I’ve put the system in ‘full heat’ by using a 9v battery between red and purple wires. I don’t ‘know’ for certain it’s correct/‘full’, but the servo stops on it’s own after maybe 30 seconds or so. (As does a parts servo I have.)
With the amp disconnected, if I put the system in full heat, using 9v, and then connect the amp, it always reverts to full cold, even though temp is set to 85. That’s why I was trying to put it in full heat without the amp, and leave it there, just to get through the winter.
With the amp connected, defrost/vents seems to work appropriately, though again, air is warm (or cool?), not hot.
The center vents are closed, when in full heat, as they should be.
As I said, I believe I checked the vacuum system on the cabin side of the firewall, and it did hold. Probably need to repeat that, to verify.
With the amp disconnected, there are very few things that can change. Obviously, with the servo static, all mechanical linkages and connected flaps will not move. In addition the servo vacuum switches will not move…so heat valve open, center dash flap closed, and lower heat vents open. Recirc flaps in full heat should be closed as well as defrost flaps closed. When turning mode control to defrost, the windscreen flaps should open directing heat to screen.
When you shut off the car, a vacuum solenoid changes state…and will open the recirc flaps as vacuum is lost…if the electric vacuum solenoid is bad or recirc vacuum actuators are leaking or stiff, they may not close each time vacuum is reapplied.
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The general test of the AC amplifier is indeed that the servo moves with changing temps, Thon - but at least the servo is operational…
One aspect of the working system is that it objectively measures cabin temps. Drivers’ feeling of hot/cold is not reliable - a thermometer is advisable. Another quirk is that whatever the set temp; if the cabin temp is above dial set temp the AC sets system to ‘cool’ - and vice versa. The range of adjustment is limited to within the ‘65’/‘85’ limits - so cabin temps should be measured, to be on the safe side…
Incidentally, (as a funny story); I got full cold set to ‘85’ (as I thought) - and dug out the wherewithal to attack the problem. Only to find that I had set ‘65’…
However; with the servo to full heat in ‘manual’ it will stay there - any variances on output heat is due to other factors. And the fact that the centre vents stays closed throughout so indicates. One thing is coolant temps, which in cold weather may vary; while the thermostat may prevent cooling in the radiator, the cooling in the heater matrix effects a considerable cooling effect. And the heating effect of heater matrix is of course a function of both coolant temps and fan/air speed. In this case; have you checked air temps at low fan speeds - using a thermometer?
As Gary says; in ‘def’ the defrost vents should open - all other inside vents should also close, except the side vents. Which should blow at the same temp as the defrost vents - ‘def’ function the same way with the servo manually in ‘full heat’…
Another factor may be the compressor. Nominally; in cold weather the compressor is shut down by the Ranco thermostat as the temp in the evaporator usually then drops below 2C. However, if the compressor engages, it will provide additional cooling until it is again shut down by the Ranco. It’s probably worth while to disconnect the compressor clutch wire for testing…
In principle, the compressor is meant to run throughout - this is to dry out the air before entering the cabin, preventing fogging. However, with low outside temps the air is already dry and the compressor is not required for this puropose - but its action is controlled by the Ranco…
There is also a ‘bias’ control under the radio. This allows different temps between the footwells and the ‘upstairs’ vents - in this case the side vents…
I’m not sure the observed temp variations is due to flap settings being influenced by vacuum - the main flaps are operated mechanically by pushrods connected to the servo cams, the servo being stationary in this case. However, Gary’s points should not be neglected…
I think some attention should also cover the coolant temps, as said above. While overcooling is not a usual problem with the xk engine; a faulty thermostat may play a part, and low temps may warrant a partial covering of the radiator. A standard procedure in Scandinavia during winter - to increase coolant temps and improve cabin heating…
with no experience in AC operation I’d only address the heat problem: If you used to have hot air, but now only receive warm air there is a chance that the system still blends or leaks ambient air into the desired stream of hot air.
If this is not the case then the heater matrix doesn’t function properly. As Frank asked before: Is the t-stat operating correctly? If it opens below 88°C in winter the engine won’t get really warm. Upon replacement of my t-stat the heating capacity improved severely. Then you might have air bubbles in the system caught in the heater matrix and wish to bleed the water circuit. Finally, are all the air duct joints still intact? It sounds like you’ve been working a lot behind the dashboard.
It took a while for me to do some more testing–and I’m no closer to solving this, AFAIK!
I’d previously done the mod that allows manual control of the compressor, so it’s not a factor–it’s off.
Coolant temps could be hotter, but it’s steady at just under 90 degrees, and I do have warm air from the upper vents so I can’t see how that could be the issue with the cool air from lower vents.
With full heat, I have good warm air from side vents only, and small bleed from defrost vents. And, lots of air from footwell vents, but it is COLD. Interestingly, if I run the car without the system on, when I first turn it on, the footwell vents put out warm air. This gradually turns to cold air over maybe 15 seconds or so??
Have also found that when switching to defrost, defrost vents put out warm air, but footwell vents continue with lots of cold air. Those SHOULD be shut, I believe.
Recirc flaps are open, and closed, respectively, as they should be.
It seemed to me the most likely cause of these symptoms was the lower bypass flap not closing, allowing cold air to bypass the heater core and go directly out the footwell vents. Using Kirby’s book, I’ve made sure the bellcrank levers are fully up, and in that position, the bypass flap IS fully closed. Loosened it, readjusted it–still the same.
My last thought is partially plugged heater core. Is it possible some/all of the lower half is plugged, so air going through that part is not heated? (I don’t know which way water flows through the core.) I think that might explain my symptoms? I know I have put head gasket sealant in the coolant twice (!), so… And the second time, it DID seal my head gasket. Maybe also my heater core?
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Partially clogged heater core is a bit far fetched, Thon…
That the defrost vents blow hot, and continues to do so, implies that the heater core is OK. Though to me, using sealant in the coolant as a precautionary action is ‘unwise’ - it may cause unwanted clogging…
That the footwell vents are open in ‘def’ is only plain wrong - if the AC amp is disabled. The system is complex and difficult to decipher without the AC amp functioning - one of the reasons why AC amp function is the first step in diagnostics…
To wit; a primary step in ‘Def’ is that all vacuum is removed from the system - basically this causes flaps to go to their default positions. Defrost vents to open, face vents closed, water valve open and inside vents closed. In principle, vacuum is removed by unpowering the vacuum solenoid - but how this is done is not specified. I would ‘think’ it would be done at the function control as the servo stays in full heat - but I don’t know for sure. But without dumping vacuum - the foot well vents would stay open…
With the servo set to ‘full heat’ manually, the footwell vents would be open to allow footwell heating of course. However, in ‘def’ the servo stays in full heat, but vacuum is removed - closing the inside vents.
One test is, in ‘def’, to disconnect the vacuum hose at the vacuum reservoir. This will definitely remove flap vacuum - and if this closes the footwell flow it will at least confirm that the flap itself is operation properly.
That said; the air flow to the side vents are manual controlled (open/close) at the vents, but the air here and at the footwells is delivered after passing through the heat/cool process - and should have the same temps. Have you checked the bias control under the radio is set to ‘red’…?
I know a partially clogged heater core is a “bit far fetched” but I’m running out of ideas!
Footwell vent not closing, when in Defrost mode, I found is due to weak canister not pushing rod up as far as it will go. When I help it, still a little air from footwell but not much. So that’s that.
Also found that in this mode I have lots of warm air coming out of the driver’s side of the unit where the hot water enters–or leaves(?). Should there be a foam plug or similar there (see pic)?
Still no change in cold air coming from foot vents, in full heat.
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More to the point, Thon - does it close when the vacuum hose is disconnected from the vacuum reservoir…?
The footwell vent’s default is ‘closed’, it opens with vacuum - if it doesn’t close properly, check for obstruction…
The cold air to the footwells remains strange. In principle the ‘upstairs/downstairs’ heater flaps move in sync, but are separate items. Like the ‘downstairs’ flap can be moved (I think’) by the bias control to increase bleed past the heater core from the evaporator/outside air to keep the footwells cooler when wanted- but it should be symmetrical to both sides…
…that it does not, implies something wrong with the air conduits - which should be checked. However, that the downstairs flap does not close with vacuum removed is a definite fault - which should be pursued as a first step. It allows the outside air to flow unheated to the footwells…
Check for linkage movement with the servo in varying positions…?
Finally–heat again!
After thinking about, staring at, and messing with the flaps for way too many hours, and deciding they seemed to be where they needed to be, I decided to attack the heater core. My hypothesis, and I’m sticking to it until facts prove me wrong :-), is that coolant passages in the lower 1/2 or so of the heater were plugged to some degree, so air moving through that portion of the core was not cooled. That air was primarily directed down, into the footwells. The upper passages were mostly open, so air moving through them WAS heated. THAT air then moved up and horizontally to the side vents and windscreen where I did have heated air.
One big clue that this was happening was that with the engine hot, after turning on the heater fan, I WOULD get warm air for 10-15 seconds or so, then it would stay cool. I think this implies there was a small amount of coolant getting into those partially blocked passages, but it was quickly overwhelmed with cold air.
I clamped the two hoses to the heater, and then removed them. Used a garden hose, and two pieces of 5/8 hose to connect to the heater inlet and outlet, and directed the outflow to a bucket so I could monitor it. Got LOTS of debris. (As I mentioned, I did put head sealant into the coolant twice, in the last few years.) Reconnected hoses, added a small amount of lost coolant, voila–hot air from the footwellsl!
Couple of caveats: I reversed the inlet/outlet flow MANY times (dozens?), by moving the hoses. This was essential, as the flow would quickly clear, but then switching direction would dislodge more crud. It would have been FAR easier to figure out an easy way of changing the garden hose from one hose to the other, rather than moving the hoses on the heater. I also found, the next day, that water from the not clamped hoses had run down the lines and into the footwell of the car. LOTS of water! So, I’d recommend clamping the two hoses used to flush the lines.
Really pretty easy job. Wish I would have done it a month ago!
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Apart from the likely misprint; ‘…that portion of the core was not cooled’ should read ‘was not heated’, Thon…?
However, in ‘def’ the footwell vents should be closed - all air to be directed to the defrost vents. In other situations the lower part of the heater core is nearest to the footwell - so your hypothesis is certainly not without merit…
