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Old 07-14-2011, 02:41 AM   #1
pprince72
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A/C quits working when it gets 90+

. .....I have a 1998 K1500 and 244,000 miles on the whole A/C system and only had freon added by the dealer about 10 years ago. The problem is the A/C works good up the upper 80's but when the temps get into the 90's and humid the compressor quits working (when I need it most) after 15+ minutes then I turn it back on maybe 15 minutes and up to 30 minutes it works good again then off and so on. The only thing I can think of is a faulty high pressure sensor?
....... My next question if I replace the high pressure switch should I replace the Receiver Dryer or just Evacuate & Recharge the system? I appreciate any thoughts its going to be in the upper 90's for the next week + and thats in Minnesota. Thinking of snow
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Old 07-14-2011, 04:08 AM   #2
MT-2500
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Re: A/C quits working when it gets 90+

Quote:
Originally Posted by pprince72 View Post
. .....I have a 1998 K1500 and 244,000 miles on the whole A/C system and only had freon added by the dealer about 10 years ago. The problem is the A/C works good up the upper 80's but when the temps get into the 90's and humid the compressor quits working (when I need it most) after 15+ minutes then I turn it back on maybe 15 minutes and up to 30 minutes it works good again then off and so on. The only thing I can think of is a faulty high pressure sensor?
....... My next question if I replace the high pressure switch should I replace the Receiver Dryer or just Evacuate & Recharge the system? I appreciate any thoughts its going to be in the upper 90's for the next week + and thats in Minnesota. Thinking of snow
What makes you think high pressure switch is bad?
Have you checked low and high side readings?
You have to have proper pressure for the pressure switches to work right.
On the 98 I have found the low pressure switches and wiring plug-in to give the most problems.
Any lights flashing or on on control panel.
After a battery change some of them have to be reset.
Is your higth switch mounted on back of compressure on yours?
Or mouted on high pressure line?
If 2 wire line on pressure line it can be checked with a jumper wire.
Or if a single wire switch in compressor it can be checked by seeing it is grounding or switching with high pressure.
If on back of compresser the system has to be pumped down to replace and then vacumed out and recharged with proper charge.

If it has been 10years since charge.
First thing is to check for proper AC charge.

What are your low and high side pressure readings at idle and at 2 K rpm?
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Old 07-15-2011, 08:53 AM   #3
j cAT
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Re: A/C quits working when it gets 90+

Quote:
Originally Posted by pprince72 View Post
. .....I have a 1998 K1500 and 244,000 miles on the whole A/C system and only had freon added by the dealer about 10 years ago. The problem is the A/C works good up the upper 80's but when the temps get into the 90's and humid the compressor quits working (when I need it most) after 15+ minutes then I turn it back on maybe 15 minutes and up to 30 minutes it works good again then off and so on. The only thing I can think of is a faulty high pressure sensor?
....... My next question if I replace the high pressure switch should I replace the Receiver Dryer or just Evacuate & Recharge the system? I appreciate any thoughts its going to be in the upper 90's for the next week + and thats in Minnesota. Thinking of snow
your making more out of this than is necessary.

since you have not had to service the ac for about 10 yrs I would say with your issues you need a slight charge. I would first get a guage set and measure the refrigerent pressures. then report back here what you found.. I would not just add some r134 refrigerent..first lets see what the pressures are..

with these vehicles made by GM at this age adding a pag 150 oil charge of 2-4 oz is needed to replace the oil lost over this long period of time ..with the proper amount of oil ,,,the system seals better reducing refrigerent lost..


WHEN YOU LOOSE REFRIGERENT YOU ALSO LOOSE OIL......

THE USE of a guage set when charging prevents installing too much refrigerent.. monitoring both high and low sides..if the high goes over about 325 at the 90deg f air temp doors open fans on max this is too much refrigerent...

the high pressure cutout safety usually never works therefore usually never fails..the low pressure switch works all the time it is a common problem ....this would require voltmeter and the pressure monitored on the low side to determine if it is defective.. at about 5 psi and above this switch should be closed..below 5 psi it will open to stop the compressor so as to protect the internal valves..must have refrigerent / oil flow when compressor rotates or the compressor will fail...

too much refrigerent and liquid enters a rotating compressor it will also damage the valves....
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Old 07-15-2011, 12:38 PM   #4
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Re: A/C quits working when it gets 90+

I 3rd the low pressure cycling switches failing alot. Sometimes a slight tap will get the switch to close again and verify. Also the connector problem. There is alot of condensation there and the terminals can get corroded even though the connector has a weatherpack seal. As far as high pressure cut-out switches on those trucks (if it is the 3 wire one in the hose), I have seen the steering linkage rub through one or more of the wires causing improper feedback. If so the wires will need to be repaired and rerouted. The way you describe your problem it sounds very much like the low pressure cylcling switch on the accumulator, esp. since you say it will work for up to 30 minutes sometimes.
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Old 09-04-2011, 08:38 PM   #5
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Re: A/C quits working when it gets 90+

Final post replaced low pressure senor and topped of the freon and works great hopefully for another 10+ years. Thanks everyone.
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Old 09-05-2011, 07:37 AM   #6
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Re: A/C quits working when it gets 90+

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Final post replaced low pressure senor and topped of the freon and works great hopefully for another 10+ years. Thanks everyone.

thanks for your repair info .. not an expensive repair ....
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