A/C Question

[svfetter]

Having Fords all my life I have had successful experience with maintaining my A/C charge on all my cars. From R12 to the current R134A. I like my A/C to be Cold, Cold, Cold!!! I have always charged my systems a little heavy (and I mean a very little on 134) and have had no problems keeping my 95 GT or 2000 Expedition operating at peak condition.

Now to the Roush. I know the intercooler in front will cut down on Effiency. Car has not been very cold from the first and I decided to add a 3oz can of booster. System took almost all. Definate improvement in cooling. Now for the question.

On my other cars the high side pressure will run anywhere from 300 to 400 PSI on a hot humid day. On the Roush (2007) the high side pressure never went above 150 PSI. So what have they changed now and how can I expect this A/C to perform compared to my other cars??

Follow Up - Upon driving A/C performed much better. Before adding - High side pressure cycled up and down from 80 to 150 constantly. After adding high side pressure remained more constant. End result was good but wondering about pressure difference.

[xzo6]

Never have been a fan of high side pressures being beyond ,the tolerated limits of the compressor.I am not saying that you have ever done that.Each system has a MAX capacity for Freon and pressure. ( you could blow the reeds in the compressor if you do exceed the amount.An expensive repair would follow if the reeds blow,since little parts of the compressor go into the system,contaminating and plugging everything up.).Most manifold gauges usually give you a visual guidline of whats tolerable.In the 60's and 70's,some A/c units in Chevys and Fords were huge 2 ton BTU units.Big enough to cool your house in the summer.The high side for those would be higher.Everything is much smaller now in the name of efficiency.Each high side range tolerance is specified for each year a car is made(as is the exact amount of freon,average 2 pounds or less , for most cars)..What you need to do is phone or ask your Ford dealer what the range of pressure is for your specific year and how much the capacity is for Freon or R134a.
The designs of A/C units change often.Case in point,GM came out with a radical variable displacement compressor for much of it's line up in the mid 90's. after R134a was introduced.There was no range on the hi and low manifold readings.It was constant.If you didn't know that it was a variable displacement model,you'd think the A/C compressor was fried,because it just kept working.It never shut off.It was their way of making an A/C compressor that would help your car save gas,since it met the demands of the HVAC system and didn't cause a load on the cars Horsepower,turning on or off.It only used enough displacement (within the compressor)to meet the demand of the system.I am sorry I don't have your specific answer to your question,but as I said your Ford service manager will give you the range.It is a specific amount.
That being said ,take the temp with a thermometer in the vent with your A/C MAX,on and windows up.If it's about 45 degrees,with the motor at 2000rpm,(put a big fan in front of your car blowing in the direction of the condenser)...you can't do better than that.Also,you are aware that R134a is less efficient than R12.They went to R134a,because,it didn't have CFC's(which is bad for the ozone layer).I don't know if Ford still uses an Orfice tube to change the pressure before the Evaporator.A simple design change will have an affect on your readings.So I am sorry,but I suggest you phone and ask your dealer.BTW,besides not having enough Freon(R134a) in the system,another culprit of cooling loss is moisture in the system.That is why I like pulling a vacuum on the system for 30 minutes,once the Freon has been removed.It dries out the system and if the vacuum dosen't hold steady,then you know there is a leak somewhere.While you are pulling a vacuum,you can dry the freon ,by recycling it.The 3 R's(recover,recycle,reuse.)...Unfortunately you need some basic equipment for that.So I am not a fan of simply adding a small can of freon to the system periodically.Just a guess,but since your system is a stock Mustang A/C unit,150psi is more than likely in the range of normal high side pressure.Higher psi would seem very high,in my opinion.But,ask your dealer.
BTW,in humid weather the length of time between cycles should decrease but each cycle will be longer.(therefore the compressor is running more often).It shouldn't affect the manifold gauge pressures too much.
This is FORD HVAC 101...Yes,GM and Chrysler use simular systems,BUT,the types of specific components are different.BTW,I am satisfied with the cold air pumping out of my Roushcharged Mustang coupe.
A convertible vehicle,HVAC system must work harder,and will seem less "cool",since the cold air escapes faster,even with the top up.I could discuss this in more detail,but that is the next level of HVAC repair.We could discuss refrigerant oil,how much oil to add after an accident destroys your condensor,etc. WARNING! IF you get your HVAC system serviced at too many different establishments,you are asking for trouble.Try an get your service at one reputable place.They will know your system and it will prevent second guessing on the part of the technician,since they know your detailed HVAC service history.I know you would bring your dog and cat to the same Vet,since you get them better care since they know your animals history.It will live longer,hopefully.Same thing for HVAC systems.

[svfetter]

Thanks for the great Response Xzo6.

Really appreciate the information and education. I suspect you are right and this compressor is smaller than that on my other cars.

I have always been careful not to overcharge system. Actually it has been easier to detect an overcharge in the 134 systems since they will start to throw warmer air if too far beyond capacity. Also I know the intercooler will have a negative effect on A/C Performance.

Having owned fords for so long and having relationships with some good techs, I believe this was just a case of a little refrigerant loss with the seating of all the o-rings in a new system. I have had more than one tech tell me that a small loss in a new car is not that uncommon.

As I said, I only added the better part of a 3 oz can. and the system responded well and I am satisfied with the current performance.

Thanks again for your response.

[trouble]

I havent looked at the ford specs yet but on all the macks and freightliners i do at work the norm working high pressure is around 150 to 175 with r 134 norm cycle around 75 to 85on the bottom side

[xzo6]

Your welcome.I don't know if the newest models of compressors have a blowoff valve.In hot.humid weather,they would open up and release refrigerent into the atmosphere.That would protect the compressor from getting damaged from overworking.Seems to me they do not do that anymore,since the aim is to keep freon in the system,and not release it into the atmosphere.The point of that is sometimes your freon level would drop,and there would be no apparent leaks.I guess it is for reasons like that ,they invented 3 0z. cans of freon.There should be a sticker under your hood telling you your cars capacity for R134a.I assume yout Expedition,may have as an option,a separate set of A/C controls,for rear passenger seats.That became popular in the 1990's.If so,it will have a much larger capacity for freon,than a normal vehicle(Because there is more A/C lines involved).Plus it has a greater cabin space to cool down....Have a good day!!!

[svfetter]

Thanks again Xzo6,

Yes the expedition does have the rear air, so it is a bigger system. Location to add refrigerant is a pain to get to. There are stickers on all my cars as to correct amount of refrigerant. How the heck can you tell??? My tech showed me how to read high side for just a little top off. If I have much more trouble I take it to the experts. I wish they still put in sight glasses so you could get a better idea what is in the system

I do remember one time a few years ago my 95 GT needed a little boost, but I could not get it to take any refrig. It was during the hot summer when you usually are going to have an issue if at all. I called my Tech and he said to spray cool water on the condenser coil every few minutes to bring high side pressure down enough to get it to take a little. Well it Worked !!!!!! I got the system over charged and it would not do any thing but blow hot air. In Fact the compressor would only run for a short time and you could hear the clutch kick out and It would not reingauge. At that point I realized what I had done and corrected the charge amount. Within 30 minutes I was crusing down the expressway with the thermometer reading a duct temp of 38 to 40 deg. Live and learn.

Every system (even the same one on different cars) is different and it takes some time to learn its likes and dislikes. I liked the old r12 systems, easier to work with and in general got colder.

Anyway - Enjoyed talking with you.

[xzo6]

I know Chrysler has a sight glass on their HVAC system,on the reciever dryer.If you see any bubbles with the system running,then your charge is low . BTW.My name is Bob...I am partially crippled now(broken neck in 1996...car accident,not my fault) I was hit by a street racer. I can't do HVAC anymore.I can't even loosen the dust caps on the High and Low ports...I like to keep up on the technology though...Worked up until last year at a Ford/Roush dealer,but my CNS is slowly decompensating.This fourm,means alot to me.Everyone is pretty cool!
But! I still am able to get my car out once a while,and that spells FREEDOM to me.Even drove once at Mosport Int'l Raceway in Ontario, in my car 2 years ago....what a blast.Unable to do it now , however. Nice talking to you svfetter.I was in Kentucky back in1978 on my way to Florida,as a University student on Marchbreak.Beautiful State.Ironically,it was snowing.That same time in Canada,the army was digging people out of their trapped cars after the worst blizzard in a 100 years.

[svfetter]

Hi Bob,

I'm Steve from Louisville. Sorry about your accident. My wife and I have our share of health issues as we age (who doesn't) but overall we are pretty lucky.

Been to Canada twice, both times to Niagra Falls. Last time for Honeymoon almost 30 years ago, so don't think you can say we are frequent visitors.

I really like this site and forum as well. It seems that the Roush owners seem to be a really great group of people. Have learned a great deal from the site.

Have a great summer and be safe.

[xzo6]

Thanks,both of you have a safe summer as well.I f your ever up to Niagra Falls in the future,give me a call!

[ponyexpress1573]

Not to hijack but I will be in Onieda sp? and then on to Niagra for the first time in Sept. I went to the Ferris plant there last year in Onieda and since it is just short distance decided to rent a car and drive to the falls this year. It was beutiful cxountry up there not what I expected being for Oklahoma.