Hi Guys,

The AC (set at 70 deg) starts out quite cold but after an hour or so (outside temp about 90+ deg), at highway speeds, the ac is blowing a tepid/cool and the inside of the car creeps up to about 77+ deg..... the floor vent seems to be "colder" than the dash vents, when this situation occurs.

For the first 20 mins or so the blower actually cycles on and off a few times, maintaining around 70 deg in the cabin.

If I stop for a rest spell of 15 mins or so, upon continuing the journey the AC starts out real cold and then goes through the above mentioned decline...and so on.

Any thoughts anyone?....after 28 years a small recharge needed? System still appears to be original R12, judging by the pressure fittings.

Where, actually, is the sight glass which (according to the owners manual) should be checked for excessive bubbling?

Heater control is set to cold.

Thanks,

Rob.

 

I'd suggest a set of gauges to see what the high side and low sides pressures are doing when the cooling backs off. With out gauge data...I 'm thinking expansion valve or low refrigerant condition is causing compressor to kick out frequently.

 

I would think maybe a potential cause would be a loose, aging, or deteriorated compressor belt might also cause the interruptions in the temperature.
Does the force of the air coming out also diminish or just change in temp? i.e. does it seem like all of the same "trap flap" style enclosures in the interior of the dash still opening fully?

 

Expansion valve pops into my brain as well here and agree with having the pressures checked...hopefully when the symptom is occuring.

But.....

With the temp control set to *max cold* (65º as I recall) you should be getting about 90% of the airflow thru the center dash vent and just a small amount from the lower vents. Is thas what it does? When the cooling seems peter out does the airflow change? That is, does the center vent close and most of the air start coming out of the dash vents and footwell vents? If so, this suggests a problem with the *control side* of the system rather than the refirgeration side of the system.

Cheers
DD

 

Thanks for the input guys......EDITED.

The cold out of the centre vent was starting at 42 deg F and over one to two hours running would increase to 65/70 degrees or so (outside in the shade temp of about 95 ) with the footwell vent showing 55/60 degrees or so. Stop for 10/15 mins and it starts out real cold and fades a little quicker.

Doug, my owner's manual says that 90% of the air flow goes to the windscreen when "defrost" is selected......also says the air only comes out of the centre vent in the "cooling mode"....that makes no sense to me; all auto ac I've seen blow all vents to start.

Anyway, so checked the pressures ( at great place that has old timers like me there), 20ish psi low side and 190ish psi high side and excessive bubbling in the sight glass (green colour...so it has maker dye in it). Put in 12 oz R12 (new at $4 per oz) and now reading 40 and 240psi.

Done two 600 mile round trips to Denver since 5 hours non stop one way....no fading of the cooling and blowing 39 Deg F at centre vent at start and holding 65 F all the way.

Cannot detect any leaks at the compressor (black light...normally used for detecting cat pee !!!!) or lines in the engine bay.....have not checked in the console evaporator yet. So not sure how long this "fix" will hold up.

I've spent a lot of time (being retired is great but the "salary" sucks !!!)
researching the Delanair Mk II System. I have come up with a theory to explain the initial problem. It is very similar to a cruddy/blocked condenser on a window air conditioner,if I don't service/clean mine every season then they freeze up after a while and blow tepid air. The difference between the two is that the window air conditioner does not have a freeze cut off switch to kill the compressor and it looks like the Delanair does...BUT is probably non functioning....so stopping for 15mins cures the freeze up (due to inefficiency of the low charge) and we have cold air again to start with.This also could explain the slightly colder air at the footwell vent. I understand that replacement Delanair control parts are non existent...so I prob will invest in a parts car...but only a really rusty one !!!!

One last point; anyone know what the capacity of a full charge in this system is?

Rob.
2006 X Type Sport Wagon.
1987 XJ6 Daily driver.

 

Sounds like you've fixed the problem




Right




Right



I think it's a matter of terminology. I think Jaguar considers maximum cooling to be 'cooling mode'.

If you select the coldest temp on the dial (65º I think) the system will go into cooling mode (max cooling). OR, if the difference between desired temp vs. actual temp is great enough, the system will automatically go into cooling mode (max cooling). Either way, output should be thru the center dash vent.

If something less than *maximum* cooling is required then the system goes into 'blend mode'.....which is a very wide range. The output might still be cold-ish, if needed, but the center dashboard vent is closed down and air is sent thru the other vents.

The same thing sorta happens with max heating. If you dial in max heating on the control knob, OR the system decides max heating is needed, almost all the air will come out of the foot vents. If something less than max heating is dialed in or needed, the system goes into blend mode and opens the outboard dash vents as well.





Well, if the problem crops up again, take a peek at the compressor. If it isn't engaged then it could be that the freeze switch ('Ranco Thermostat') is working. If the compressor is engaged either the freeze switch isn't working or the evap core isn't freezing.

Cheers
DD

 

Thanks Doug,

I edited my previous post. replaced "cruddy/blocked evaporator" with"cruddy/blocked condenser".

How should I test the "Ranco Thermostat" if I ever get to it?

When I first noticed this initial problem I stopped (at idle) a few times to check if the compressor was engaged or slipping belt etc. ,could see no "gap" at the "clutch" plate..so yes engaged also double checked by switching of climate control ... immediate increase in idle speed by 100+ rpm. So I think the Ranco is non functioning, hence a slow freeze up due to, initially, low R12.

Rob.
2006 X Type Sport Wagon.
1987 XJ6 Daily driver.

 

40 on LO side and 240 on HI side is little too high unless it's really hot.

Total capacity is about 2 1/2 lbs of R12. I run about 28-30 low and 180-200 high.

 

in Full Cool Mode, (TEMP at 65 and SELECTOR in AUTO), air comes out of the Center Vent AND the corner dash vents, 1 blower on each side keeps the air volume pretty equal on the side and center vents. Make sure the side vents are actually in the OPEN position.

mounted at the bottom of the passenger side Blower Assembly, close to the firewall side of the interior, (fresh air intake area), there is a "thermistor" sensor that gets full of crud from the centuries, check it with a flashlight to see if it is clean and if not, a used toothbrush works great to clean it. Pure maintenance item.

leave the RANCO thermostat alone, it rarely fails.

another possible failure is the AMPLIFIER, but the way you describe it, it sounds like the system is working fine.

the following link has good info on the Delanaire system:

Delanair Mark II Automatic Climate Control