I just had my a/c recharged and now the fans are always running at the highest speed when the a/c is on (96 with 2-speed fans). Is this normal? I know the fans are supposed to be on when a/c is on, but I can't remember the high-speed fans always being engaged like this.

Thanks,
Patrick

 

Low speed fans should come on with the a/c. Is your SES on?

 

Thanks for the reply. Nope, no SES. The fans go to high speed right after turning on the a/c, regardless of whether the car is warmed up or not.

I had to get the low pressure valve core replaced, so they discharged, evacuated, and refilled the a/c. I hooked it up to a scan program, the high side a/c pressure looked a little high but low pressure looked ok. Is there a correlation between high side a/c pressure and fan speed?

Thanks,
Patrick

 

Two follow up questions:

1. Is it normal for the fans to go to high-speed mode when a/c on, but engine temp < 200?

2. If not, what makes the fans go to high-speed mode besides engine temp? I'm guessing the PCM must be looking at some a/c parameters, but not sure which ones.

I want to know if the high-speed fans could be coming on incorrectly due to the a/c high-side pressure (or low-side) being too high.

Thanks,
Patrick

 

I have not found anything that tells me that the PCM changes fan speed due to a/c pressures, but it seems it is possible.

 

yes. AC pressure is directly related to fan operation. at aprox 246 PSI high side pressure the fans should come on. depending on ambint temp, condensor screen condition and pressure the fans might stay on as long as the AC is on.

you might wanna pull off the radiator shourd and look inbetween the radiator and the condensor and see if it's got a trash bag, dirt, wasp nest or other debirs covering the condensor screen. this would cause higher pressures. but it;s possible they just slightly overchagred the system

 

Curious as to where this info is from? I would like to educate myself in this matter.

 

it was used in responce from someone I trust with there info. and backed up by every GM ac system I have worked on. Head pressure raises with the fans off while your charging the system. then right about at 250 PSI high side the fans come on. . just like I can tell you that Gm systems with low pressure switches will open at aprox 50PSI high side pressure. I don;t have any specific refference materal for you but I think that I have a book on it at work. if I do I will scan you some of the important things and email them to you. the 3 wire pressure switch on the AC line near the pass shock tower is what provides the PCM with pressure information for fan control

 

Thanks for the replies. I finally found it documented in Book 2 of the GM service manuals; it states the high-speed cooling fans come on in the following situations:
- certain DTCs set
- ECT sensor greater than 234 degrees F
- A/C head pressure above 248 psi

Depending on what caused the fans to come on, the high-speed fans will shut off when either:
- temp drops 5 degrees
- A/C head pressure drops to 208 psi

I can get the exact page numbers if anyone is interested to reference it.

Had the A/C checked this morning; apparently there is some restriction somewhere in the system which caused the high side to stay too high. He put less in it this time to prevent the high side from getting so high, system needs some work though.

Patrick

 

I find it hard to belive that there is a restriction on an expaionton type system. usualy with a restiction the low side pressure will fall (sometimes pull into vacuum) and the line on the inside of the restiction will literaly freeze up. have you replaced the compressor? had any other problems? I would like to know what the low side pressure was in relation to the high side.


Thanks for finding the refference material to back me up. I was afraid I was goona have to sort through a few hundred books that we had at work to try and find the exact number

 

The compressor appears to be leaking, the low-side valve core was just replaced as it was leaking. I have had to recharge it every few months since last summer.

The high side was getting up around 350+ (never below 250 since the fans were always on), the low side was staying in the normal range below 45. When I took it in today he was seeing around 400 on the high-side. The low-side was apparently slow to discharge, and slow to charge. He only put in 1.5 lbs to prevent the over-charge on the high-side. Is this consistent with a restriction somewhere?

I know very little about the a/c - where do restrictions typically occur? The guy at the shop I went to indicated the drier was a likely source. What's the worst case scenario if a restriction occurs, and a line freezes?

Patrick

 

without seeeing it it's hard for me to say but it doesn;t sound like a restriction. it sounds like overcharged or high head pressure.

have you had any work done to the fans? are they spinning the right way? (pulling)

is there any trash or debris on the inside of the condensor inbewteen the radiator etc that would restrict airfloe from the fans?


the compressor is definietly working since it is able to achive such high pressure. drier failure is very rare. I ahve only seen it once .

if fans and airflow are ok then if it were me I would be thinkikng about it being over charged, pull the freon out, place it undera vacuum for 20 mintes and recharge it to the right amount. if after that it;s still high on the head pressure I would start suspection the H valve.

if the low side was puling was down past 20 (espcialy with throttle) I would suspect a resrtcion but base on what you said I don;t belive so. if it was an orifice system I might be inclined to agree but since it's an expantion system it;s not likely

 

HBH thanks for the info. Fans are working correctly, just cleaned off the condenser when I put in a new radiator month or so ago. What is an "H valve"?

If you get a chance I would like to hear the difference between and "orifice" vs. "expansion" system. I'm guessing the valve that regulates the flow to the evaporator can expand somehow in an expansion system but not in an orifice system?

 

the H valve or expantion valve is mounted on the evaproator case on the outside where the 2 lines screw in.

in an oriface system the orifice tube is a double sided screen that aids in the convertion from a liquid to a gas. cause of this screen any depris in the system gets caught in it and it can get pluged up. thats why anytime when you have the system open it's good to replace it.

I can not really go very much into detail about exactly how the system works or I might feed you some false info. I was never taught how the system works. just how to fix it. I need to do some reading up on it tho so I can have a little better understanding on the difference.