Well.... I was having problems with my A/C shutting off at stop lights, and I couldn't figure out why... I hadn't used my a/c for about 6 months so I thought that maybe I had a leak...

My father got out his freon recharge/testing kit and hooked it up to the appropriate connections...

The guage was showing over 400+ psi on the high end on the guage, and around 50-70 on the low end... while the compressor was engaged.... but the compressor would turn off and the pressures would drop way down... He told me he had never seen this before...

Then all the sudden the radiator fan came on and then the compressor stayed on, constantly... then the pressures went the the right numbers... 70 or so on the low end, and 210 on the high end...

When I am driving the A/C works perfectly, the only time it stops is at stop lights etc... so the logical conclusion is that it is related to cooling issues. The radiator fan cools some A/C "radiator" if I am not mistaken, and it needs this because when you compress freon it gets very hot...(I am pretty sure of this)

No matter what at Idle (once the temp reaches 220F) it will not put out cold air. Once you start getting some air flow at about 10mph it will put out fairly cold air, then when you get to normal traffic speeds its perfectly cold, feels like about 60...

So what I am wondering is...
1. Is there a pressure sensor turning off the compressor? Or is computer-controlled temp sensor or what?

2. If the compressor is indeed turning off because of pressure that may or may not be related to heat of the freon, then why the heck is the fan not ALWAYS on (at least at low speeds) for the A/C system?

For now I just turn off my A/C when I come to a stop because I don't want those high pressures destroying my A/C system...


Thanks for any input... It's starting to warm up here in Texas...

 

also would it be advisable to create a connection in the HVAC controls to manually run the fan at all times? Or maybe I could simply create some fan control that no matter what when my car is in ignition mode that the fan comes on under a certain speed... (This seems possible because of the electronic speed sensor)--We have that right, because I've pulled an error code before which made my speedo read zero, for some reason while my tach still worked fine...

 

You definately need the fan running with the a/c on (especially at idle)! The fan should come on when you turn the a/c on. I think there is a switch on the high side line that tells the fan to engage...

 

you think maybe its a bad relay? or sensor somewhere?

 

Sounds like you overfilled it. I thought that the low side pressure was supposed to be about 35 and the high around 200-250 with the AC on.

With the AC off, the low side will be a lot higher and the high side will be very low...because the compressor isn't engaged...

It is possible you have a blockage in the compressor, the condensor, and/or the receiver/dryer assembly.

I would buy the haynes Heating and AC book they sell...a LOT of useful info in there including specs for pressure, capacity and troubleshooting your A/C system.

HTH,

 

Your low side reading with the fan on is double what it should be, You should see 30-40 with r-12 and 25-30 with 134a Your hi side at 210 w/fan on is okay. It looks as if your overcharged somehow, The fan should run when your hi side touches about 190-210 psi so the fan going on will drop the pressures and it going off will raise them. If your system is filled correctly it could be a problem in the compressor. If it were me I`d pull the system down and check the orffice valve for clogging or metal(it can elevate the pressures if filled) The reciver dryer`s desecant bag can also clogg if the compressor is coming apart and raise the pressures. If you need your low side at 70 psi to get the high side to 200 it`s either 10 degree`s out or your compressor is shot

 

ditto, either there's a restriction, or its overcharged. BTW, is this single or dual fan setup

 

okay I have a single fan... but I am not 100% sure about the low side, but I know that once the fan came on that the low end, and the high end went to the proper pressures... it's only when the fan turns back off that the pressures rise so damn high. What I am wondering is there a relay, sensor or something that makes the radiator fan come on at an earlier temperature? When the fan comes on, or I start moving (even at 10 mph) all the sudden it will start blowing 60^f air out the vents. But once I stop at a stoplight (and its not hot enough for the radiator fan to come on), as soon as my engine temp reaches 220^f or so, (which happens rather quick with the A/C on) then it starts blowing hot air, then the compressor shuts off completely, and you can feel it kick when it's cycling on and off.

I wonder if the fan is supposed to come on early.

I also think that the pressure gets so high because the freon gets so hot from not having any active cooling on it when the fan is off.

 

I believe the fan should be on all the time when the a/c is on. Sounds like an electrical problem to me.

 

can someone with a/c confirm this? See if your fan comes on even when your engine is cold... on a single fan setup.

If it is supposed to, that will be a pain in the ***, could be an electrical problem in the hvac controls

 

Yep it should run as long as the ac is enguaged. A good way to decrease the air temp is either to install a dual fan setup or an aftermarket puller fan works great as well. For some reason I cant remember where the ac relay is located but that seems to be your problem.

 

bah... I was just talking it over with a local shop on the phone, and he said that its probably not a relay, but more likely a sensor, or the computer itself... but I wonder if the computer handles the A/C at all on our cars... I still think its a simple little relay, or transistor...