A/C pump on and off

[Novasmithjohn]

I just replaced the a/c pump on my 99 Tahoe. Used 8 oz pag150 and 2lb 134a the pump cycles on and off until the engine start to get warm then it will not stop running. Is there a sensor that is going bad and causing the pump to stop running?

 

[exp500]

Switch position matters, compressor runs on defrost also. So... More info needed. What are your Pressures/ Temps after charging system?

 

[Eman85]

System is CCOT, clutch cycling orifice tube. It cycles the clutch to control the flow of freon and the clutch is controlled by the pressure switch at the accumulator. Did you follow all directions and replace the accumulator and orifice tube along with flushing the system? Are you monitoring pressures when the clutch cycles?

 

[Novasmithjohn]

When the compressor runs the pressure is 25lb at 65 ambient air temp and 60 when the compressor is off on the low side. The air temp at the vent is 49. Changed the accumulator and oriface tube. New condenser and evaporator. Didn’t flush

 

[exp500]

Would be better if you had hi side pressures and humidity too. As a guess, I would say you are undercharged. 27-30# is kinda normal for 65 degrees.

 

[Novasmithjohn]

I’ll get another can and add it and see if it improves the operation of the system. Will post result. Thanks for the help

 

[Novasmithjohn]

got a nother can and put it in have a solid 30 lbs now but have to power the clutch off the battery i have power at the switch on the acumilator and at the the switch mouted ontop of the compressor, but there is no power at the switch on the back of the compressor. I dont have a deacent wire diagram for the a/c system only the one that in the haynes paperback. which is foe the trucks does anyone one have adigram that is for the Tahoe? Thanks

 

[Eman85]

Top of compressor is the clutch wires. Back of the compressor should be high pressure cutoff switch that provides ground. All of this from memory so it comes with a disclaimer.

 

[east302]

I dont have a deacent wire diagram for the a/c system only the one that in the haynes paperback. which is foe the trucks does anyone one have adigram that is for the Tahoe? Thanks

Here’s the diagram from 1999. The full manuals can be downloaded at the link below (see post #77):

88-98 Service Manuals

I looked at every post, there's lots of excellent info in this thread! any chance there is a link for a 1991 GMC Suburban V1500 manual that can be shared? On the forum, search the engine thread " service manuals " look at all the manuals, find your year, 91. It will cover all the models based...

www.gmt400.com

 

[Novasmithjohn]

Thanks for the information and the diagrams I replaced the high-pressure switch and have the other 2 on order. I’ll post what I find. went to get the downloads and it wanted me to download a game is that correct?

 

[exp500]

went to get the downloads and it wanted me to download a game is that correct?

Probably not! Usually thats a sign of a virus or malware in your system. Thats always been a good site 4 me.

 

[east302]

Thanks for the information and the diagrams I replaced the high-pressure switch and have the other 2 on order. I’ll post what I find. went to get the downloads and it wanted me to download a game is that correct?

Try post #111 in that link. It looks like another member posted another 1999 copy onto a Google drive.

 

[Novasmithjohn]

Ok thanks

 

[Novasmithjohn]

Try post #111 in that link. It looks like another member posted another 1999 copy onto a Google drive.

View attachment 423458

Got the service manuals and they were a big help. Also found info on the Chevy forum. I have changed all the sensors and replaced the plug and diode for the clutch and plug for high pressure switch. The compressor will run now for about 5 sec an shut off for about the same period of time and then repeat the cycle for about 5 minutes. If I shut he truck off and let it cool down for an hour or so when I start it again it will do the same thing again. The ambient temperature is about 65 Humidity around 55 low pressure will drop to around 25 and then go back up to 60, the high pressure will go up to about 80 and then down to around 60. I don’t know if it’s low i put 5 12 oz cans in and I don’t want to blow the seal out of any thing. Any suggestions?
Thanks. I used an after market condenser if that would make any difference

 

[exp500]

Do you have a laser thermometer? While compressor runs, shoot temps upstream/downstream of each component.
Also look for charge sticker usually on accumulator.

 

[Novasmithjohn]

Do you have a laser thermometer? While compressor runs, shoot temps upstream/downstream of each component.
Also look for charge sticker usually on accumulator.

Yes I do. What should I be looking for on the accumulator. I'll check the Temps Monday we have company this weekend. Thanks

 

[exp500]

Yes I do. What should I be looking for on the accumulator. I'll check the Temps Monday we have company this weekend. Thanks

Pressure drop lowers temp, so if there is an obstruction, say from a failed compressor or a clogged oriface valve..... every piece in the system has a change. So a Big change or a No change is something to think about.
Search 4 Seasons for a charge weight for your trucks configuration. I remember seeing 64 oz. but don't recall config. (Rear Air/ Towing package, RPO list from glove compartment.).That is estimated amount. Service A/C using Hi/Lo gauges for final amount. Good luck.

 

[Novasmithjohn]

thanks