billschroeder5842

My AC is confusing me on my 91 ZR1


It was running great in the Texas summer heat and then about two weeks ago the cooling began to get steadily worse. I thought it was a leak in the system.


I got one of those Auto Zone 134a and a gauge combos, found the system was low, gave it a squirt and it worked, back to normal for about 2 weeks. The gauge read Green at about 43ish.


Friday the AC started to act up again and the diagnostic light came on the climate control and I got the "09" meaning low Freon, which makes sense as it did nothing for the leak. The AC Clutch was not engaged.


I put the AC charger back on and the gauge show readings in the red-- like 60! I let a bit of pressure out of the system and the gauge dropped accordingly and in fact into the green/45, however the diagnostic continued to show low Freon and the AC did not engage.


I went through the FSM and followed the procedure (undoing battery, wait, run for 5 minutes, run recirculate) still no AC clutch and AC gauge shows full but still getting the 09. I wonder if I'm, getting a false reading as the system is not circulating?? Could one fo the AC pressure switches have gone bad?


I'm a novice on AC so I'd appreciate some guidance!


Thanks!

1LEZ

Pulling a vacuum on the system is pretty important to making sure the charge is good. Do you have a vacuum pump? Its usually good to pull a vacuum test for 30 min to an hour and then see if any bleeds of. Usually another 1/2 hour or so will tell the tale. Not sure if this helps. Hope it works out soon. Where in TX? That is where I am located too

billschroeder5842

Southlake, up in the DFW metroplex.


Sorry, no fancy AC equipment, just me, FSM and a bottle squirt.


I'm going to throw a low pressure cut off switch ($12) at it tonight and see if that makes a difference. If not, I'll end up taking it to the professionals.

secondchance

Bill,

Unless the system had been converted (and it may have been since you were able to charge with 134a), 91 came with R12 system.

One thing to check is 2ndary fan operation when the motor is cold and with AC turned on. Normally, 2ndary cooling fan will not come on until the coolant temp reaches 212 degrees (if running factory chip. If running Marc Heibeck chip this temp is normally set at 205). However, even at below fan turn on temp, turning AC on will turn on the 2ndary cooling fan.
If fan does not come on even with AC turned on, high pressure switch (used to turn on 2ndary fan) is suspect.

Goldcylon

What he said usually when these units go it there is excessive oil around the body seals of the AC unit however replacing the switch is not a bad idea as well.

billschroeder5842

Thanks 2ndChance and GoldCylon- Here is where I'm at at the moment....

*The squirt bottle gauge says 60lbs (red) so that has me stopping there as I worry about over fill.
*I replaced the low pressure switch by the coolant fill tank for good measure.
*I pulled the negative cable off the battery for the reset. Upon restart the AC clutch cycled on/off about 8 times in less than a minute before just stopping as the 09 code came back. Sorry I don't remember if the fan cam on or not.
*I do have a Haibeck chip

I agree on checking the high pressure switch--where it it located? I'm at work so no FSM manual. Oh, is there a difference between the switch it self (specific low pressure/high pressure) or does it just read and send the info to the ccm? I'll pick one up on the way home.

I drove her to work today- it was 49 to start the day in Dallas with a high of 75 so no AC needed!

secondchance

High pressure switch (a.k.a. AC cooling fan switch) is specific part - not interchangeable with low pressure switch.
As for the location, it's close to oil dip stick on the passenger side. Two wires going to a connector.

https://www.corvetteforum.com/forums...flowcrop-1.jpg

billschroeder5842

Thanks for the help. I ordered one and will pick it up on the way home.

Hopefully the switch is bad and a swap will solve the problem!

secondchance

Once way to check real quick is by disconnecting the switch. Once disconnected, ECM will be fooled into thinking that there is high pressure and command the 2ndary fan to turn on. See if this allows AC to operate.

If and when replacing high pressure switch, un-thread slowly and be prepared to close it if you detect freon gas leaking. I noticed shrader valve at times will fail and stay open.

Was this system converted to R134a?

billschroeder5842

Yes, it was converted to 134a.

The parts store had the wrong one (not threaded) so the right one will be in tomorrow. More to follow....

ambrowns

When you get the reading in the red is the compressor running? If not, that is why. Without the compressor running, the pressure will even out between high side and low side and will read in the red on the pressure gauge. You have to get the compressor running before you can get a good reading as well as the abliliy to refill with the typical refrigerant cans.

To troubleshoot while getting the 09 low freon code, you must disconnect the negative battery cable first for at least 10 seconds. Then unplug the low side sensor and put a paper clip into the two female holes in the cable to act as a jumper. This will tell the AC that there is sufficient refrigerant in the system and will engage the compressor. That will allow you to get a good pressure reading and continue to troubleshoot.

I am thinking you just have low refrigerant and need to find the leak.

billschroeder5842

Genius! Thank you for the suggestion!

I disconnected the low pressure side, jumped the connection and the compressor came on. I added refrigerant until the gauge said about 35--- the system was blowing cold. It is about 65 in my garage.

Here is what I noticed... could be normal, could not be...

On the "squirt gauge" the pressure needle would move based on if the fan was running or not. If the fan was running the pressure dropped and held steady at 12. When the fan was off the pressure would rapidly build until 35 (in the green) and once hit 35, the fan would go on and the pressure would drop again to 12. Once at 12, the fan shut off and the pressure woudl uild... and so on. The system (with the jumper) would bounce between 12 and 35 and the compressor ran all the time (as it was jumped).

I "un jumped" the connector and clipped it back on the low pressure side switch. The AC clutch engaged and ran normally, except.... I noticed that the clutch engaged until the fan came on then the clutch would go off. When the fan shut off the clutch would engage and when the fan went off the clutch would engage, then go off, then on then off again until it stayed steady... until the fan came on and the clutch again went off.

I watched this "fan on, clutch off, fan off clutch on" for about 6 cycles.

Whats up with that? The little thermometer inside the vent said 56 degrees, idling in my garage.

Normal or not? whats next?

-=Jeff=-

Was the car previously converted to R134a? You also have to reset the C68 controller when you charge the system. I would suggest pulling vacuum and then charging to the correct amount of R134a. It probably will not get as cold as the original R12 and the head pressure will be a touch higher but should work well

ambrowns

I’m no AC expert so I could be wrong, but I don’t believe your psi should ever drop below 20-something or the compressor will shut itself off to save itself. You might still be too low on refrigerant, but that is different behavior to when my refrigerant was low and the low pressure switch jumpered. What is your pressure with the AC turned off?

One other thing to consider that I didn’t see mentioned was whether you added oil back to the system. Since a good amount of refrigerant (including oil) was leaked out of the system, you should make sure to add oil as well to ensure the compressor doesn’t fail. The r134a can that you used might have oil pre-mixed in, but I would check to make sure.

billschroeder5842

I dunno...

I'll mess with it when I get home tonight and see if the pressure changed at all and what the pressure is with the system off.

Thanks for your help

billschroeder5842

No joy...

The pressure was up 24-50 but still did the "hunting" clutch on-off with the pressure needle going up and down. Funny the "on" part of the clutch cycle dam near killed the engine a couple of times?

I pulled the negative cable and attempted a reset; no difference. The clutch came on/off several times and then threw the 09 code.

I think I'll just take her in to "my guy." I'm sure it is something simple I'm just not "getting."

ambrowns

24 PSI is still pretty low and depending on how accurate the gauge is might even be a bit lower. I’d say you should try to get the PSI up to at least 30 on the gauge with the compressor/fan on. If it is still cycling then, I would agree that you should take it in. Either way, good luck!

billschroeder5842

I'm happy to try and add more so the "bottom" pressure is 30 but but I worry that the high pressure moves into the red?

ambrowns

When the compressor is off, the low pressure side should read anywhere from 80-120psi depending on the outside ambient temperature. That is perfectly normal. Once the compressor turns on, the high pressure side will go up to around 200-250psi (I assume you do not have a high pressure side gauge to check this). The low pressure side should read about 30psi and not cycle higher or lower. If it cycles to lower than 30psi, then you don't have enough refrigerant in the system.