'85 XJ-S.

Had my car on the vac pump for almost a week now...no telling if it's ever been charged anytime in the last 20 years, so I'd run the pump for about an hour, then let it sit overnight...by the end of the week it held 30"Hg for 36 hours. Frankly, I never thought that'd be possible.

Tried charging it today with R134 (changed drier and o-rings a couple weeks ago). I had always wondered if "65" on the dial meant it would try to maintain 65, or if turning it all the way was the "on" signal that would act as a max cool setting. Well, it's going to try and maintain 65...and no colder. This is pretty annoying when you're trying to charge with a temp probe, because ideally you want to put a load on the system when you're charging but if it keeps on maintaining a 64-66 degree output temp it's hard.

Is there any way to jump out the amp to go to a "max cool" condition? I ended up running the heat for about 30 minutes (which, again, will only reach 85) then switching back to cool and back and forth. Once the sight glass finally cleared I was showing about 50-55 on the suction side and 275 on the high side, but again I couldn't really load the system up so I'm not really sure how effective this is. I even tried opening the glove box and resting my wife's curling iron on it so the heat would hit the indoor temp sensor. This helped a little bit, I'd hear the doors move and the discharge temp would drop to about 61 or so, but then go right back up in a minute or two.

In the end the only thing I had to go by was the sight glass clearing. What a pain. I never worked on any car's AC that absolutely refused to allow the driver to make any decisions at all.

D

 

Darel
That hole in the top front of the dash roll, above the glove box, is the entry point for the air that goes over the airtemp probe (situated down that hole) that gives the airtemp signal to the system.

Take a hairdryer, and a charming assistant, set dial to max cold, and get said assistant to blow hot air down the hole. The the aircon will then run at full chat cold.

The water valve (back centre of firewall) should close under these conditions. Good idea to make sure it does.

Greg

 

Darel, Are you sure your system calls for R134A? A MY85 may still be using R12 and you can not mix or change over without changing the compressors oil.

If 134a is correct your 50-55 suction pressure sounds a bit low but I don't have a refrigeration chart in front of me for the correct range. Your numbers will change with temp change. Pressures and temp are directly related. If you look at your suction gauge you will see temp readings,, mine on on the outer ring. This will tell you at a given pressure what temp your evaporator is running at. At 55psi if I remember right your evap will be running around 30 degrees F. NO this is not good, if the evap is below freeing the mositure in the air will frreze on the evap face and block the air flow. A correct charge will keep the evap above the freezing point.

By knowing your suction pressure you know your evap temp and vice-versa.

 

Thanks Greg, already tried this with a heat gun and a curling iron. I had the heat gun blowing into the footwell to raise the inlet air temp (since I didn't know if the system would go into recirc or not, so I was loading the system either with hot engine air or hot footwell air) and the curling iron sitting propped up on the open glove box door. I didn't want to use the heat gun / hair dryer on the temp sensor because I was afraid of melting the dash. I could hear the flaps open and the outlet temp would drop to around 61 but then a couple minutes later come back up to 64-66.

In the end I cleared the sight glass and just called it good.

I have to say the system seems to want to work perfectly - it's holding 65 degrees right on the dot - but if you're driving the car and the sun is beating right on you, the system has no real way to recognize that 65 just doesn't cut it, especially since if you leave it in auto it drops the fan speed down too. Very disappointing!

The ATC in my '07 Chevy pickup is garbage, does virtually nothing automatically except regulate temp, and the manual controls are so poorly designed as to be dangerous to use while driving. My wife's '02 Jeep Grand Cherokee has a phenomenal system, best I've ever seen. Regulates what outlets are open, dual zone temps, even knows when to put it in defrost (accurately!) using the auto-wiper sensor. Plus, everything on it is manually selectable too. Only problem is I'm averaging a complete teardown every two years or so on it - blend doors when I first bought it, resistor pack a year later, just a couple weeks ago replaced the evap core, and now just on Friday the resistor pack died again. The Jeep doesn't sense inlet air temp, it has two IR sensors aimed at the driver and passenger's stomachs. Don't ask me hpow it doesn't always read 98.6 but it works great. When it works.

D

 

Has anyone ever rigged up a "max cool" switch, maybe something using a specific resistor that would bypass the inlet temp sensor and force the amp to think it's like 150 degrees in the car? Maybe using an SPDT relay that would toggle back and forth between resistor and thermistor?

 

Darel,

Your system is overcharged. If you see only liquid in the sight glass using R134A in an R12 system you have significantly overcharged it. You should recharge with R134a and 90% of the capacity of R12. The sight glass is useless for R134A systems. You need to use a scale.

I have a 1985 which I converted years ago. If you run at 65 it gets plenty cold in the car. So cold that my son and I were freezing in the car but it was 99 degrees outside and humid. The windows were getting condensation on them. I run at 70 degrees and it is cold but comfy.

 

Thanks Greg.

Drove the car to church today, about 75-80 and cloudy, and without the sun beating on me, 65 felt chilly. Very nice! I believe what you say but I can't see how it would have gotten so cold as to cause condensation - must've been over 90% humidity outside.

Need to keep in mind that there's no real reason for the British to design something with regard to "direct sunlight", a foreign concept for them.

D

 

Like I said very humid out. The point being that the system when charged properly will cool very well.

 

Darel

Something else important I forgot to mention.

First: remove the (US) driver's side "cheek" panel from the side of the tunnel (the one with the footwell vent in it - just unscrew the two self tappers holding in the vent and ease the panel out and slightly forward).

Second: get your head in there are look behind the maze of wires about 2 or 3 inches in horizontally, and you will see clipped to the bottom of the steel aircon unit, a cigarette packet-sized object with wires coming out of it going to a small round multiplug. This object is the aircon amplifier. On the side facing out towards you, you will see a small plastic/electronic looking adjusting screw set into the unit (often a slightly different colour (eg blue or brown). A small flat-bladed electricians screwdriver will adjust this. ANTI-clockwise means more cooling for a given temperature knob setting.

I suggest you give this a quarter turn anti, and then try the car out without refitting the panel. If it is still not cool enough, give it a bit more. This item is NOTORIOUSLY unreliable and eventually gives up completely, and new ones are not available for love or money. There used to be a firm in Australia that made new ones but they have not had them in stock for 2 years to my certain knowledge.

If you have the aircon running and you adjust this trim screw, you can hear its changed position making the comprssor cut in or out. I think this will do the trick for you, as mine car is the same model delanair, and it will freeze the occupants at 100° plus outside.

 

@Clamdigger - I'm showing 50-55 on the suction side which works out to about 50-53F. Sucks that I have Celsius gauges but it's easy enough to convert.

@Greg - I actually just replaced my amp a few months ago. It's spot on adjustment-wise and don't really want to go playing with it. I mean, according to my cooking thermometer, it is within less than a degree of setpoint before it starts to react the system.

It actually worked very well yesterday, was out driving for over an hour. I just had to turn it off in order to get home. Yes, that compressor sucks that much gas! I went from about 14 mpg on the highway with the AC on to over 17 after I turned it off.

 

Darel

Glad the amp is Ok. But if it is not cold enough for you, just give the amp a 1/4 turn anti, and see what gives. It cannot break anything, is very straightforward to do, and will probably fix the car so the temp feels right.

Greg

 

Good call, thanks Greg!

 

If you have 50-55 psi on the low side your system is most likely over charged of you have poor air flow over the condenser. What is your high side pressure when reading 50-55? Try spraying the condenser with water and see if the pressures drop significantly. Since you stated you charged it until the sight glass was clear you can be certain you have the system overcharged. A/C needs the proper charge to work effectively. More is not better. Now that you have fixed the leaks why not go to a shop and have the system charged with the proper amount?