Further to my post a week or so ago I have had my A/C recharged and now it gets all cold in the truck but there are a few questions that the A/C guy and myself couldn't answer. Can you help?

1) Does the compressor cycle on and off when the A/C in the cab is set on?
2) Is there any other mechanical 'switches'/valves on the a/c system other than the electrical clutch switch on the filter/dryer canister?

Reasons behind question:
1) Mine seems to stay on all the time when the a/c is switched on. The clutch cycle switch was open circuit before I got it gassed so I am guessing it acts as a safety switch on low pressure to prevent the compressor working. Does it also brake contact at high pressure?
2) The a/c guy said there are usually thermostats and a highpressure switch to prevent the system from freezing. The haynes Book of LIes only shows one switch in the circuit diagram (the clutch cycle switch)

Thoughts please.

Regards


Simon

 

The compressor should cycle on and off, and relatively quickly at that. If yours is not cycling, it is most likely because it needs refrigerant. A system that is low on refrigerant will not cycle. And not only that, if it does not cycle, you should not use the A/C at all until the problem is corrected. If you do run it when it is not cycling, it will eventually freeze inside of the system and possibly ruin A/C components. The reason that the compressor is designed to cycle is to keep the system from freezing. If it starts to freeze, you will be able to see it, it will have white frost on the underhood components, and you will probably get a mist coming out of your vents or even small pieces of ice. It can get to that point quickly too. The fact that it is running constantly would serve to negate the low freon charge - so the cab will get cool but you will freeze the system and possibly burst hoses, or the condensor, or mess up the compressor (it's just like a tiny engine with a piston or two inside of it). Imagine something freezing in one of your motor's cylinders while it was running, if that was possible.

The A/C guy that you quoted above - he doesn't strike me as being the sharpest knife in the drawer. Those should be very simple questions for a supposed A/C tech. After seeing what he was stumped by, I would not trust the guy to be able to properly fill your system. If it is R134a in there now, you can go buy a can and hook it up, and top off your system. You don't even need gauges for that simple task. The system will not take more than it needs, and you can look at the sight glass to make sure that it is full. All you will need is a can or two (most likely just one) of R134a and the special hose and valve to attach it to the system - it's a special hose that locks on the the top of the can and has a **** that you turn to puncture the can. After puncturing the can, you use the same **** to turn the flow on and off and regulate it. When you puncture it, the needle will be in the hole and the can is "off." When you back the needle out with the ****, the hole opens up and the refrigerant comes out and flows through the hose into your system. To stop it, you just turn the **** back in. It's a simple and efficient design. But all that you really need to do is to look at one of these hoses and it will be self-explanatory, so don't get too hung up on learning it now.

BTW - that hose is not that "special," it is most definitely needed but the last time that I bought one it was around $1.99. That was a few years ago, but still, they should be cheap. As long as you can buy one, I think that someplaces made them illegal to sell, to discourage the average shade tree mechanic from working on their own A/C and releasing freon out into the atmosphere. I'm sure Ebay or someone on the net would have them though. And every time I go to a flea market I see lots of them. Heck, I had to release freon into the air before, before we really knew what it did to the atmosphere. I had to empty the system to make a repair so I just removed a hose and blew three pounds of freon to Jupiter or wherever it goes (about $150 worth of R12 in today's world!). But don't do that! Mine was years ago, we know better now.


If I recall correctly, the system has two valves that have different size threads - so you cannot fill the wrong side. But check to verify that before you attach it. It is CRUCIAL that you attach it to the correct valve, unless you enjoy a face full of shrapnel.

The whole procedure is very simple and no tools are needed at all except for the hose and valve deal. You could go to the auto parts store and get what you need, and then put it in in the parking lot and be on your way in fifteen minutes.

HOWEVER - we still do not know for sure that your system is low on refrigerant, although your symptom indicates a low charge about 99 percent of the time. Run the system and look at the sight glass - if it's bubbly then you need more refrigerant.

As far as other switches, I am not positive. I have rebuilt an A/C system once, on a 72 F100. That truck had a switch that controlled the cycling of the compressor - you could adjust the amount of time that the compressor runs, although it is actually a thermostat and all you are doing is raising or lowering the temperature threshold for the compresor cycles. I don't think that your system has one of those per se; as far as being adjustable. It certainly has at least one thermostat. Which brings me to a second thing for you to check, yeah you guessed it, the thermostat. If it is bad then the system either would not cool at all, or it would run constantly until it froze up.

A/C is not the mystery that people think it is, it is actually a fairly simple system once you have familiarized yourself with how it works, what parts are involved, and what their functions are. A/C shops are notorious for taking advantage of people wh have not taken the time do learn something about their A/C system. Good luck and let us know how it turns out, or if you have any more Q's.

JB

 

I tried to post a link to the hose at JC Whitney but it kept taking you back to the home page. But you can go to JCWhitney.com and enter these part numbers to see them. They are all that you need to add refrigerant to a system, aside from the refrigerant itself.


http://www.jcwhitney.com/autoparts/S...-10101/s-10101


ZX511293Y


ZX511300A

 

I know that when my rig gets low on refrigerant it would cycle on and off every 3 to 5 seconds. It just kept going click, click, click. I know it is suppsosed to but not that often. Like JBronco said, check it yourself if it is r-134a. I bought a guage for mine for about 7 bucks. Just make sure you hook it to the low side(the cold one) or like JBronco said, Boom! Also, if you check it or add freon, make sure the truck is running with the a/c on max.

 

Yeah that can happen also. Both can be symptoms of low refrigerant. The bottom line is that usually, if you are having compressor cycling issues, such as not cycling at all or cycling on and off every five seconds - the problem is with low refrigerant.

 

Thanks JBronco, very comprehensive answer. Further to what has been said is that the system was vacuumed and filled with 1.3KG (3lb) of refrigerant (a substitute for R12 as R12 is illegal in the UK- but not r134a) and it does cool ok. This figure was gained from a ford fleet site and various people on here. After filling it I noticed a sticker on the accumulator that said fill with 1.25KG of R12 so the amount is ok.

I think the problem is with the cycling switch. I need to know more about what it is and how it works. Having studied the circuit diagram for the system I can only see one electrical switch that controls the compressor clutch which is the one connected to the accumulator (fliter/ dryer or whater you call it). If there are no other switches then maybe the fault is with this switch. Now I initially assumed it operated on pressure alone - i.e. low pressure (no gas) and it broke contact. Now maybe it works on temperature too - i.e. low pressure or too cold and it switches off.

I've studied the switch and note there is a screw recessed between the electrical contacts in the switch - I suspect that is the calibration screw for the on/off states so I'll have a look at that and see if I can manually tune it.

One a perfectly working system how often does the compressor cycle?

I know this is very subjective and depends a lot on outside air temp but what would you expect the temp of the air coming out of the vents to be when it is set on normal A/c and cold? mine was reading about 3-4 degrees C with the outside at about 6-7 degrees C.

 

addendum - I don't believe one can buy cans of refridgerant off the shelf here - you have to remember we're a cold country so A/C is still only generally fitted to high end luxury cars.

The guy who serviced mine was pretty knowledgable and I do no a bit about A/C as I have looked after A/C in IT server rooms before but he was just not familiar with US systems (I know the thermodynamics ain't changed in 1000 years!).

 

Air from a properly operating A/C system will enter the cab on max @ 42°-45° Fahrenheit (6°-7° C.) on a standard day. (Sea level @ 70°F or 21.5°C) Ambient air temp and altitude play a great role in the discharge temperature. As JBronco said, any A/C tech should know the system of heat exchange and controls. My compressor cycles every 60 to 120 seconds this time of year around 70° with a full charge. (Father in law is owner of A/C company re: info above.) Once your system starts to loose charge it will cycle more often. Once it has lost charge it will not initialize. The adapter to charge the Ford is unlike that of other makes, I bought one for my FIL to use in maintaining my truck and other Fords. As you are mostly at sea level in Great Britian and usually a little more humid/cooler than not, you could see 3°-4° C from the A/C vents, I guess. Also, per JB, I think I'd get a second opinion on the system.

 

Sounds like from what you are all saying the actual cooling cycle is working ok I just need to get it to cycle the compressor off so it doesn't freeze. Will take a look over the weekend.

Thanks for all your help.

 

I believe you are correct, sir. All the best. And bye the way, what do you think of the Charles and Camilla thing? Wife is an avid Di fan, has been for years, and I get to ask a real subject person the question.

 

Of course, if the actual cycling switch itself is bad, it could cause a problem. I think that it is a rare problem though, I have never had it happen to me or seen it happen to someone else. I have never really heard of a "cycling switch" per se, at least not by that term. I know that there is a low pressure switch on there, and they are a common problem area. They are easy to fix though. Just replace it. If the low pressure switch goes bad then the system will act like it is empty. I had it happen to me and at first we thought that I blew a hose or seal, but then found that the system was full - and so we looked to the low pressure switch and it was bad.

 

Ill throw my 02cents in on ac . I assume we are talking as the ac being on cold. Gauge being turned to the coldest setting. Now i am curious also and i think ive read of a blend door that allows heat to be mixed with this when turning ya **** back a little( red).Compressor shuts off and there has to be a thermostat some where . Looking at books of other cars i see a blend door( mabey operated off vacuum instead.I do know by driving trucks diesels the cold /hot valve( whick sends hot water to your heater coil) is operated by the temperature switch. Hadnt really given this alot of though for our broncos but had to install a valve on my car so i didnt have to take the whole dash out (temp fix)Car has a eletronic thermostat gauge( digital) 65degrees to 85 degrees and curious to what that operates (blend door) mabey an expert can verifythe simple language to all this THANKS TR