Scorpio A/C Troubleshooting

[john keefe]

Interestingly enough, other than a thread about the A/C cooling fan, ain't much in the search data base about troubleshooting the Scorpio A/C. Or, of course, I could also be a compleate idiot. Thanks for objecting so vigorously, but its true, it really could be me.

Caveat: I know nothing about A/C systems, other than basic principles. Charging is about the most I've ever done. It's be nice to have an easy solution, but I'm not holding my breath. I'd also like to not need to take it into some repair shop at this time of year when everybody else is trying to fix their A/C.

Anyway, I've got a fully charged A/C system, but almost no cooling. 105psi on the high side, 100 on the low pressure side. Compressor sounds like its knocking, and never made that noise before. Manuals says it could be the 3-way expansion valve, but I have no way to testing w/o evacuating the whole system. It has a Rapido expansion tank sitting in front of the evaporator & fan.

I remember there's a diode issue/cure in line around those wires, but I'd like to start with the most basic probable causes

[zxr250cc]

Hi all,

Servicing an AC system in a shop usually involves them evacuating the system, opening it up and changing the bad parts, vacuum pump out the system and then fill it up again. Due to the nature of the design of AC systems there is little else you can do. If the compressor is failing it will dump small pieces into the full system requiring a complete system flush and new condenser along with new expansion valve and compressor. Many parts places require the full system change out and flush kit to offer any warranty.

You mention that the system is full. Is it over full? That makes it not work well also.

Cheers

[john keefe]

Thanks. Don't know if its overcharged... its converted to R134a, but all I can find in the manual refers to R12 weight and psi. Both high and low seem to be within range in the table. I expect a 32 year old system to be just about on its last legs, though it was fine last summer and w/o the knocking noise. Never did blow adequately enough, though.

[zxr250cc]

Hi all,

The operating pressures in the system are higher with R134a than with R-12 and that was why some folks tried alternative coolants in the systems. R-12 is still out there with some folks but having changed to R-134a it would not make sense to try to change back. If you decide to have it checked or fixed be sure to change all the little valves as well.

Do you have one of the charge coolant cans with the meter on it to show the charge level as low, good and then to high? They are not precision gauges but they are some info or if you know a good mechanic with an AC recovery system you might ask for a check up with the idea of doing the work as it fits your budget.

On AC, I use a mechanic with the recovery system since those don't let gas escape when servicing. The kits for the meters and hoses are around one hundred or so and good money spent if you are actually doing your work yourself on more than one car. A small vacuum pump will be around the same, maybe a bit more. If you choose to do this yourself the 4 Seasons expansion valve ($30) would be a good choice from Rock Auto or maybe one of the guys in here has some NOS Motorcraft AC stuff? The no name cheap parts stuff is not a good choice for this kind of work.

Here is a link for more info: https://www.4s.com/en/ecatalog?year=1988


Cheers

[brokencase]

I might as well chime in here as I am in process/limbo with Scorpio A/C work.

My story..
So I converted to R134 back when I had acquired the Scorpio back in early 2016. When I received the car I had to replace the lower coupling O ring that comes out of the condenser. I had to do this same job on my previous Scorpio.

It ran fine for 6 years on R134, but every winter it would loose a bit of refrigerant. So I would have to top it off. Another forum member suggested that the compressor front seal was probably leaking.

So this year I decided to change out the compressor. I put a watch on a rebuilt compressor on ebay and procured one for $100.
I put the new compressor in. It was a pain. but it went in and the system holds a vacuum.

I ran into the problem that it would not accept the new charge. I could get no flow of refrigerant into the system. I don't know if it is the Schrader valve on the compressor or if it is the three way pressure switch that is not activating the compressor, which would then allow refrigerant into the system. I was going to try activating the compressor manually with clip leads. I thought maybe the Schrader valve was clogged. I tried removing the Schrader valve on the compressor but it was not moving and I did not want to break the valve.

In any case, I ran out of time so I have put the Scorpio A/C project on the back burner because I have begun the restoration of my late brother's Triumph GT6 MkIII.

I still drive Scorpio, despite the heat. Windows and sunroof opened. At this point I am pretty well heat acclimated. Working on the GT6 in the uncooled garage, as well as a 61 mile bike ride to the shore in 98 degree weather two weeks ago.

[Ed Lijewski]

FWIW replacing that high pressure hose O-ring near the frame rail by the compressor is a pain because of limited working space if the compressor is in place, even when moved as far as possible towards the engine. Ugh.

Connecting the vacuum pump hose to the compressor manifold Suction port, and having the system hold pump vacuum, points to the Schrader valve functioning properly for that operation.

Possibly the hose end you used to charge the system with refrigerant isn't depressing the Schrader valve sufficiently (BTDT). Try another fill hose if possible.

It's unlikely the Trinary switch could block refrigerant flow as its switches sense pressure (...but stranger things have happened). On an XR I did have a Trinary switch failure; the system was working fine before and I had some JY units in my stash and on installing one of those the compressor activated. Don't know how to test those; I'm guessing by removing it and bench testing it with a MM for continuity when depressing the pressure valve end

Compressor seals always leak a small amount if refrigerant over winter unless the system is periodically operated briefly to circulate the oil charge on seals and O-rings. So your original compressor almost certainly is still operable if on system recharge adequate correct refrigerant oil is added.

Re the Schrader valve on the Suction port, I ruined one manifold Schrader valve port when, with that compressor off the engine, and using a valve removal tool, the tool ate into the inside of the port as the valve wasn't budging. So, exercising caution there is prudent.

YMMV

[Ed Lijewski]

John:

If it were my problem, I'd replace the expansion valve. I've replaced a few already (four cars). You can do it

Some new units came with a couple correct O-rings, other units didn't.

YMMV

[zxr250cc]

Hi all,

If you use your car only a bit in winter a good way to keep the AC system happy is to use the defroster for ten to fifteen minutes when you are running it around. That of course makes it use the AC to dry the air. You get dry heat and the AC system stays happy. Just a thought and guessing most of you knew this.

Cheers

[john keefe]

Thanks guys. Ed, agreed (at least from what I read in the shop manual) that the expansion valve is likely the culprit, which could also be causing the compressor to knock. I'll have to check into how to evac the system (probably just find a shop).

Ah yes, just another Merkur service quandry... Do you spend the time and $$$ to simply evac, replace the valve, re-charge and hope the knocking goes away, only to find it needed a compressor too. Or, do you gamble and invest in a new compressor at the same time, never really knowing if its necessary, but saving time by not having to do it twice.

[Ed Lijewski]

Re your compressor assuming it's "mileage" is around or beyond 100K the likelihood of the clutch seeing its end day is not far off. So that's in itself a reason to consider installing a remanned or new unit at this time along with the expansion valve and receiver/dryer.

YMMV

[john keefe]

Not worth repairing just the clutch? Hadn't thought about the reciever-dryer... guess I'll have to stock a few months bankroll on my SS checks before I can tackle this one. By then, it'll be Fall, and won't need the AC, so I can put it off for another 8 months! Yeah!!!

[zxr250cc]

Hi all,

Sub assemblies for a lot of stuff, like the clutch on a compressor, are going away as folks sell whole parts only for stuff like this these days. It is less trouble to swap whole units of things than to take the time to take something apart and replace only the worn portion.

Control arms on cars are a good example of that as they come with bushings and ball joints installed and you swap the whole part very quickly.

AC service would be a complete compressor swap and not trying to spend time working on the clutch. If you are paying labor the repair is less because no extra time is spent in replacing the clutch but swapping a unit in as the old one is removed. Less labor time = less money spent. YMMV

Cheers

[Ed Lijewski]

The compressor is a Denso found on several Toyotas of the same era = parts available.

YMMV

[brokencase]

On changing the compressor, what I discovered is the single hex bolt mounting the tubes to the manifold was "unremovable" in my case.
This means you can only remove the 4 bolts holding the manifold to the compressor with the tubes attached. This complicates things slightly (removal) but it is manageable. I would recommend that you do not attempt to remove that single bolt.

Ed, I still can't be sure if it is the three way pressure switch preventing the A/C clutch engaging, or if the Schrader valve is bad. If the valve is stuck/clogged I will still show a good vacuum. So at this point I have not eliminated the Schrader valve.

I think at this point is to force the compressor on with clip leads and see if that allows it to accept a charge.

But as I stated previously... I have a full plate. As my father has succinctly expressed. "You got too many wheels"

[Ed Lijewski]

That bolt if OEM is a Torx style. I've removed one successfully; and also stripped one on another car (removed the manifold plate and drilled it out). Replaced each with hex head bolts.

Re uncertainty about the Schrader valve, connect your car compressor hose to it for a shot of air; disconnect; then depress the Schrader valve with a finger nail or small screw driver tip. If air is released, the valve is good.

YMMV