AC pressure affect low speed fan?

[Slow T]

Just what the title say's my AC doesn't blow cold all of the time and the previous owner told me that he some how lost pressure in the system(can't remember his excuse).
But it doesn't seem like my low speed fan is working,and sometimes after the car has been idling awhile the car stumbles to a real low idle like a big load has been put on it.I'm digging into my BCSM as I type this,just wanted to know if I should get the system converted and up to pressure first before I go through the diagnostics in the manual,because it doesn't seem to say anything about checking refrigerant pressure except for high pressure.
Thanks for the help.
Bill Chapman :top:

[SuperSix]

Just what the title say's my AC doesn't blow cold all of the time and the previous owner told me that he some how lost pressure in the system(can't remember his excuse).
But it doesn't seem like my low speed fan is working,and sometimes after the car has been idling awhile the car stumbles to a real low idle like a big load has been put on it.I'm digging into my BCSM as I type this,just wanted to know if I should get the system converted and up to pressure first before I go through the diagnostics in the manual,because it doesn't seem to say anything about checking refrigerant pressure except for high pressure.
Thanks for the help.
Bill Chapman :top:

A/C pressure doesn't have anything to do with fan speed operation.. Maybe the blower's going bad and simply can't spin fast enough at low speed. I just replaced mine, 15.00 @ Autozone, lifetime warranty.

You'll know is too low, as the the compressor won't run. The switch attached to the accumulator is the low pressure swich, the one in the lines behind the compressor is the high-pressure switch. You can manually engage the compressor by jumping the terminals of the lowpressure switch.

When it "stumbles", is it the A/C compressor engaging? If so, something else is wrong, shouldn't stumble when the compressor engages.

[scottyb]

I interpreted this differently as SuperSix. Please clarify which fan you're talking about.

[SuperSix]

I interpreted this differently as SuperSix. Please clarify which fan you're talking about.


Sorry, I was referring the the A/C blower motor..

If it has a bad bearing, or dirty/greasy brushes, it will spin slow or not at all in a low speed setting.

[Slow T]

I'm sorry I should have stated the engine cooling fan. :stupid: :joint:
Also the compressor seems to cycle too much,and doesn't stay engaged long.
Thanks
Bill Chapman

[SuperSix]

I'm sorry I should have stated the engine cooling fan. :stupid: :joint:
Also the compressor seems to cycle too much,and doesn't stay engaged long.
Thanks
Bill Chapman

You may have a bad low-speed fan relay. The fan shoud turn on when the A/C's on. Frequent compressor cycling indicates low pressure..

[Slow T]

Thanks guy's :shakehand

[scottyb]

BTW, the fan should run on high when the AC is on, not low. Low speed is triggered by the chip when the temp reaches chip setting. High speed is ALWAYS on when AC compressor is on -or- when high temp switch in intake manifold closes.

[Slow T]

Ok Thanks :mat: :susel:

[scottyb]

Sorry I didn't mention this b4. If the fan does not run high, then a relief valve may "dump" freon to protect the compressor (like a blow-off valve). Although I'm not 100% sure on the Buick, I've personally had this happen on a late 80's blazer and a 92 exploder. Both cars had faulty/inoperative cooling fans. If your fan doesn't operate on high, this may be the reason the previous owner "lost freon". On the other hand, I've read that it is a pressure switch that triggers high speed, but I don't know the details. It's either a pressure switch or just the same circuit that hits the AC clutch. :yessir:

[mgmshar]

Direct from the 1987 Buick Service Manual, Chapter 8 (Electrical Diagnosis), Page 8A-31-6:

CIRCUIT OPERATION

The Coolant Fan is electrically operated and is turned on when the engine coolant becomes hot enough to require cooling. The Low Speed Coolant Fan is controlled by the Low Speed Coolant Fan Relay. This relay is controlled by the ECM and the Low Speed contact of the A/C High Pressure Switch. The High Speed Coolant Fan is controlled by the High Speed Coolant Fan Relay. This Relay is controlled by the Coolant Fan Temperature Switch and the Hi Speed contact of the A/C High Pressure Switch. When any one of these components grounds the coil of one of the relays, that particular fan runs. On all cars, the Coolant Fan Delay Relay operates the Coolant Fan for a short period of time after the engine is turned off. A Solid State timer relay removes the path to ground for the Coolant Fan Delay Relay coil to turn off the fan. Refer to Section 6E for conditions that will cause the ECM to turn the fan ON or OFF.

I read this and the stuff in Section 6E. The only way the cooling fan will turn on with the A/C is if the A/C runs enough to build some pressure in the system. If the A/C system is undercharged, the A/C compressor will not run, the system will not build pressure, the A/C pressure switch will not close, and the cooling fan will not run. The ECM does NOT turn-on the fan when the A/C is turned on. The only time the ECM controls the fan is when it turns-on the low-speed fan due to the coolant temperature going above the specified value in the chip. Make sense?

Here's a simple test: with the car COLD on a warm day (well, at least 50 degrees), turn on the A/C. Look at the compressor clutch. Is it engaged, or at least cycling?

1. If the answer above is "Yes", then most likely something is wrong with your fan control. Things to check: low-speed fan relay, A/C pressure switch, the wiring going between them, or the fan itself.
2. If the answer above is "No", then most likely your fan is not running because your A/C system is undercharged. When you charge-up your system, your A/C pressure switch will close (when the A/C is running), and that will trigger the fan.

Also note that the fan can run at either low or high speed when the A/C is on. On cooler days, when the A/C system is not building up high pressures, the fan will come on low speed. On warmer days, when the A/C system is building up very high pressures, the fan will come on high. If anyone cares, 260psi in the A/C system is required to trigger low-speed fan. 300psi is required for high-speed fan.

The service manual is a wonderful thing, and you can download it for free (well, you should give a donation) from TB.com.

Good Luck,

[Slow T]

Thanks for the info Mike I've looked up the same stuff in my BCSM.
I just haven't had time to get to the actual hands on stuff,between lots of hours at work,and removing injectors to get cleaned and tested.
I found that the #1 injector had a rotten O-ring in the intake side earlier this week and finally got around to pulling them today.
As far as Donating anything to TB.com,I'd rather stay away from the Drama.
Thanks again:Bill Chapman :wave:

[SuperSix]

Thanks for the info Mike I've looked up the same stuff in my BCSM.
I just haven't had time to get to the actual hands on stuff,between lots of hours at work,and removing injectors to get cleaned and tested.
I found that the #1 injector had a rotten O-ring in the intake side earlier this week and finally got around to pulling them today.
As far as Donating anything to TB.com,I'd rather stay away from the Drama.
Thanks again:Bill Chapman :wave:

The donations do NOT go to TB.com, they go to Jeremy, who with Scott Simpson's help scanned the entire manual onto a CD.

See THIS (http://www.turbobuick.com/forums/showthread.php?&threadid=100444) thread. It's a TR must-have, and Jeremy's a good guy.

[Slow T]

Hey thanks for showing me that post I'll definatly be sending him a donation,even though I already have a BCSM,somebody that takes that kinda time to put out something as helpful as that deserves some recognition.
I just really want to stay away from the BoardVS.Board stuff until it's resolved(if it get's resolved)That's why I came here :rock:
Thanks:
Bill :cowboy:

[SuperSix]

Hey thanks for showing me that post I'll definatly be sending him a donation,even though I already have a BCSM,somebody that takes that kinda time to put out something as helpful as that deserves some recognition.
I just really want to stay away from the BoardVS.Board stuff until it's resolved(if it get's resolved)That's why I came here :rock:
Thanks:
Bill :cowboy:

It's a lot easier to navigate the CD version.. And a lot more compact. :D