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Wingover
New User
May 7, 2016, 7:59 PM
Post #1 of 4
(1768 views)
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Hi All,
Ford Fiesta 2011 SES model.
Compressor is cycling on and off every 5 sec. I connected gauges and got the following (outside temp is 68F):
1. With compressor on - Low is 28psi and high is 300psi
2. With compressor off (ac switch inside is still on) - Low is 48psi and high is 280psi
the AC cools great when compressor is on for a minute and then warmer air comes out of the vent (not hot air but not cold at all) this goes on and off all the time.
Any idea what could be the problem?
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
May 8, 2016, 12:07 AM
Post #2 of 4
(1758 views)
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Re: AC cycle on/off
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First thing is IMO it's too cold @ 68F if accurate to know too much for sure but there are things you can check.
With those pressures quickly cycling and still getting high side that high I think system is shutting down from higher pressure than you have time to see - it's too high.
Why: Fans probably don't come on has to be known and should be on almost instantly with A/C request.
The other first thing is A/C is totally NOT DIY friendly and take a strong base of understanding and equipment to even begin. Came up short of info I believe on this exact car so say if a CCOT or TXV set up if you know.
What history of anyone touching it do you have or repairs already done? Seems a lot of problems with a vehicle this new would either be damage to a part or someone messing with the charge thinking they could make it better and now that's unknown or worse contaminated.
With temps lower than a real 80F known for sure coming in thru grille is what the car knows as ambient temp not other guesses or readings from a forecast or thermo from a another place you really need to know the real temps vehicle is dealing with.
If you must try to know it can work properly now for when it warms up more and really needed you really need to begin with some stuff known like it has the correct charge which would take recovering all refrigerant and putting back the exact amount stated on sticker under hood and then see what works or doesn't. Said, fans should be on especially with higher than expected high pressure reading for that temperature.
Here's a good read for what to expect for charging a system that includes what you would expect if everything was normal and can learn the bits of info like what pressures to expect at what temps from that.
High side alone at a raised idle, fans on should really settle at ~2.5 X real ambient incoming air temp in Fahrenheit and no more for example. You've exceeded that way too quickly already.
Take the time to read this which is posted up top of this section and come back with some more info and questions it may bring up and answer the ones I already asked,
Link to that "Charging Procedures Thread" is full of info worth understanding..........
http://autoforums.carjunky.com/..._A/C_SYSTEMS_P45460/
Best thing is when in doubt ask and don't do anything especially refrigerant wise till situation is indicated to do so,
T
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Wingover
New User
May 8, 2016, 3:40 PM
Post #3 of 4
(1747 views)
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Re: AC cycle on/off
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Hi Tom,
Thanks for replying. I have no history record on this. We got the car a year ago and everything was fine with the AC. We did a trip to Arizona where the outside temp got to 86F and than started to notice that it wasn't cooling all the time. The only think I did was changing the cabin filter inside the car, thinking that if it is clogged it might cause a problem with the temp sensor. I thought that the AC was working better after that. Other that that, no one charged or played with the system.
Its hot today so I am going to try again to check the fan operation (I am 99% sure its working fine) and will spray cold water through the grill to see if the high pressure will drop and I can get the compressor to run longer.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
May 8, 2016, 7:31 PM
Post #4 of 4
(1743 views)
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Re: AC cycle on/off
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This is what caught my eye on this Quote">>
1. With compressor on - Low is 28psi and high is 300psi
2. With compressor off (ac switch inside is still on) - Low is 48psi and high is 280psi<<"
Call that 28L X 300H pressure @ 68F. Now guessing that was at idle? Way to high for high side as said. That suggests it isn't "transferring" heat or an internal blockage. Seems if you have at least a year of history without touching it that's some history to go on that it wasn't overcharged.
Cabin filters and any bugs, or reason for any air flow blocked seems rules out. Idea is crossing off a list of easy common reasons first and you are.
Need real temp readings and not sure where you are getting your stated temps? If the car has a thermometer I swear some are not thermometers on the car at all but rather knows its location and what temps are reported! Whether I'm a tech or not was shocked in another's vehicle with OE thermo in it parked in full sun was obnoxiously hot all around it and thermo was still reading about what a forecast would be!!!!
From your quote the pressures when compressor was off was just taking some time to equalize back to where they would end up both the same not important unless that was several minutes of being disengaged.
The 2.5 X real air temp rule at say 1,500 RPM stands. Do the math as the refrigerant (most just say Freon) is very temperature sensitive. The high pressure will cut off A/C operation on purpose if much higher than that for any reason. If it didn't it would either blow out by an overpressure valve or break something so there are protective things to shut it down if only for a while when out of spec that far. Bet it was worse and you just didn't see it.
The end all is what you should do about it? Said this is such a maze of info to collate for the exact conditions you are in at the time you are checking pressures with unknown accuracy or operation of your particular gauge set.
This isn't for everyone and not DIY friendly stuff as already said. More folks harm systems by messing with them than solve anything so for now just collect info and think this should go out for leak finding and call it a vacuum out all refrigerant and charge to spec then see how it performs. Get's pricey as most folks aren't going to have all the equipment when everything obvious is ruled out you need a baseline that it's properly charged THEN the diagnosis AFTER that is more valuable.
Next and just observe for this for now. Look for stains and evidence of oil on parts. Run finger under connections, look at condenser for a stain collecting dirt and if all oily around front of compressor. Just info gathering for now.
A/C is its own subtrade to automotive service - know that. It's also costly to do and lots worse if something done wrong so be warned.
So right now just look for oil stain evidence and suggest you get a separate thermometer for real and fast temperatures. There are "meat" type thermos for A/C or I prefer the wired household type IN/OUT thermometers like you'd hang the probe out a window as some are very fast and accurate. No waste to own one anyway IMO for the $10 they should cost.
Go slow. Need to know if this is something you'll be able to take on or much more cost effective to send out. Knowing just that is an accomplishment!
Tom
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