A/C control problem

[Mike G]

Hi Gang:

I'm new to this group and need some guidance. My A/c will not operate and the light on the head unit flashes. I know this flashing means that the pressure in the system is low. I however cannot bypass the low pressure switch to trick the system into running. The three relays behind the glove box appear to be operating correctly, so..... Can there be a problem with the head unit/switch itself or what???? Oh, BTW, this is a 92 GMC K1500.

 

Thanks all, --Mike G

[snoman]

Hi Gang:

I'm new to this group and need some guidance. My A/c will not operate and the light on the head unit flashes. I know this flashing means that the pressure in the system is low. I however cannot bypass the low pressure switch to trick the system into running. The three relays behind the glove box appear to be operating correctly, so..... Can there be a problem with the head unit/switch itself or what???? Oh, BTW, this is a 92 GMC K1500.

 

Thanks all, --Mike G

Why would you want to trick it?? Low freon can take out compressor as the return cold freon cools and lubes it. Add some freon to it.

[Mike G]

I needed to have the system operating in order to add freon, which I opted for a conversion kit to the 134 stuff. This time the head unit flashes as if the coolant is low, and I cannot bypass the system, this is why my thinking that something else may be wrong. I have tested the three relays and they appear to be operating correctly, just kind of fishing for the next possibility...

 

--Mike

[snoman]

I needed to have the system operating in order to add freon, which I opted for a conversion kit to the 134 stuff. This time the head unit flashes as if the coolant is low, and I cannot bypass the system, this is why my thinking that something else may be wrong. I have tested the three relays and they appear to be operating correctly, just kind of fishing for the next possibility...

 

--Mike

The low pressure cut out switch is on accumulator/dryer. You can jumped past it with a paper clip

[MCourson]

I think he tried that but it did not work. I had that happen on the 94 here. Replaced the presure switch and it worked. If you do replace the switch make sure it comes with a new O ring. The O ring is an uncommon half size and the wrong one will cause it to lose charge in about 2 days.

[snoman]

I think he tried that but it did not work. I had that happen on the 94 here. Replaced the presure switch and it worked. If you do replace the switch make sure it comes with a new O ring. The O ring is an uncommon half size and the wrong one will cause it to lose charge in about 2 days.

If you are talking about the low pressure switch, if he disconnects it and jumper past it and it still does not work. replacing the switch will not fix it.

[MCourson]

Im talking about the switch on the acumulator... Yes it will work, I have done it.

 

If you are low on freon and you jump it with a paperclip the compressor will kick on. If the switch is broken and stuck with the circuit on the system will think it is low on freon.

[snoman]

Im talking about the switch on the acumulator... Yes it will work, I have done it.

 

If you are low on freon and you jump it with a paperclip the compressor will kick on. If the switch is broken and stuck with the circuit on the system will think it is low on freon.

True, generally though if everything is working correctly, you can start dump freon into system and compressor will kick in you enough freon has entered to partially pressurize system. Inverst can and put a few can as liquid into the low side of system and you will get a part fill quicker that way. I assume you did vacum system out and add correct oil too as 134 is not compatable with R12 oil.

[MCourson]

Im not sure when they switched from R-12 but the 134a conversion is probably worth it do to the scarcity of 12. My 94 has always had 134a in it. When we did mine my uncle used the machine at his shop ot evacuate the system and refilled it with freon and oil.

[snoman]

Im not sure when they switched from R-12 but the 134a conversion is probably worth it do to the scarcity of 12. My 94 has always had 134a in it. When we did mine my uncle used the machine at his shop ot evacuate the system and refilled it with freon and oil.

With GM it was with the 94 model year I believe. I know that I had a compressor replaced on my burb under GMPP in 93 and if I had waited until 94 to get it replaced (I found out after the fact) they would have converted it over to R134a. Mine still has R12 in it and I have a small stock pile of R12 and I plan to keep R12 in it too as long as I own it.

[MCourson]

We had a about 2lbs left but my sister's 93 Mazda sucked it down. Around here the lowest price is about $60 a pound.

[snoman]

We had a about 2lbs left but my sister's 93 Mazda sucked it down. Around here the lowest price is about $60 a pound.

It is a lot cheaper on ebay averaging $25 to $35 an can in lots or 2 or bigger including shipping. I have seen it go for around $20 a can in large lots once or twice and I have seen single cans go for over $40 sometimes.

[Mike G]

Alright guys, let's try this on for size...

 

Last year, my system which sees minimal use was to the point where the pressure was low, determined by bypassing the low pressure switch and kicking on the compressor. At that time I converted over to the 134, there was nothing left to my system (don't ask how I know) but did not have it evac'd (yes I am a cheap Ba$!&@). Now, my head unit is flashing low pressure, but the bypass trick does not work and it will not take any additional 134 into the system. My thoughts are that the controller/actual switch on the dash may have an issue..

 

--Mike

[MCourson]

My guess would be the pressure switch.

 

[snoman]

Alright guys, let's try this on for size...

 

Last year, my system which sees minimal use was to the point where the pressure was low, determined by bypassing the low pressure switch and kicking on the compressor. At that time I converted over to the 134, there was nothing left to my system (don't ask how I know) but did not have it evac'd (yes I am a cheap Ba$!&@). Now, my head unit is flashing low pressure, but the bypass trick does not work and it will not take any additional 134 into the system. My thoughts are that the controller/actual switch on the dash may have an issue..

 

--Mike

What year is this truck?