i'm looking for someone to shine some light into my issue.... my AC compressor will not turn on unless i put ground to the AC relay. When i force ground to the AC relay, the AC compressor turn on and the AC is cold, but once i take ground out, the compressor will not turn on at all

Here are what i have done so far,

tested AC relay with new relay
tested the fuse with new fuse
check the power fc computer wire to make sure everything is good
checked and add more Freon into the system

It’s HOT in Houston so I need some help , I would take it to a local mechanic but i figure I ask here first.

 

The Body Electrical Troubleshooting manual in the stickies has fairly comprehensive AC testing procedures. The thermoswitch is common failure item, but you may also just be low on refrigerant (in which case the low pressure switch will stop the compressor from engaging).

 

When was the last time it worked? Did it just fail? Have you done the PFC A/C relay mod? Check your thermoswitch by jumpering it. If you have done the above then you may have the up until recently unheard of internal PFC failure that I had https://www.rx7club.com/power-fc-forum-47/anybody-had-pin-1l-c-output-failure-859340/

 

it was working with the powerFC last week but I flush the radiator and took out the smog pump and noticed couple days later that it stop working ( might just be a coincident )
I was thinking of putting in more Freon to see, what’s the ideal PSI on the low pressure that it has to be on?

 

unless i am wrong it is not the low pressure switch due to the fact that the low pressure switch is inline with the compressor + feed after the ac relay is engaged. follow the circiut from the control side of the relay to ground. does the ac switch led light up when depressed? this signal also goes through the hazzard switch

 

i'm not sure myself, but the AC light does come on and also the idle jump up to about 1100 or so...

i'm thinking about taking it to a shop if i can't figure it out...

 

Like 7tist said, the pressure switch doesn't seem to be the problem since you can turn the clutch on at the relay. I think you should check your thermoswitch. Search around, somebody had a decent picture of the thermoswitch location and which wires need to be jumpered to bypass it. If you find that the A/C works when you jumper the thermoswitch, you need to replace it. If it doesn't, you may have the failed PFC transistor.

 

thanks for the input, i will try that tonight

 

Switch is here (the black box on the platform on the side of the evaporator):



You need to jump the two green coloured wires on the white connector.

 

If the thermoswitch does turn out to be the culprit. it would be in your best interest to change out the expansion valve while you have the condenser out to replace it, especially if it is the original. Don't leave the terminal jumpered, as this is what prevents the condenser from becoming too cold and freezing up which could damage the expansion valve, the condenser, or the compressor.

 

There...fixed that for ya.

 

yea yea, you got what i meant didn't you! I'm an electronics guy. HVAC isn't my specialty.

 

Sorry, I am an HVAC tech, why change the expansion valve? They are usually the last thing to fail... unless these particualar ones have some sort of deficiency??

BTW the first thing to happen if the thermoswitch is left jumpered will be freezup, and this likely won't damage anything untill it gets really bad and starts flooding back to the compressor. You'll know this has happened when the airflow completely stops at the vents, and in that case just leave fan running and hit the a/c switch.

You probably want approximately 35psig on the low side, depends on what refrigerant etc. There is actually a sight glass on our cars located on the receiver. It looks like a little glass window about 3/16" in diameter. This is the best way to guage refrigerant charge, it should look clear. If you can see bubbles, which will likely look like foam traveling through the line it's undercharged.

 

I have heard of a them failing, and mine did, so my philosophy is better safe than sorry. Plus your in there anyway, so why not.

 

jump the two cable and the compressor still wont turn on, i'm going to put back the factory ECU and see if the PowerFC is the issue....

 

+1, I agree. After 30 years, I have yet to see an expansion valve fail, per se. What does happen, is that the metering orfice can get crud in it -or- the filter screen found on some plugs up. These can usually be cleaned or blown out, with some care....

I don't recommend fixing anything on an a/c system that isn't known to be broke; especially if the system is intact and has not been broken or exposed for any length of time.

There is a workaround for the thermoswitch problem that uses a small "pilot" or slave relay that has been discussed in these forums before. After replacing the T-switch once and having the same failure reoccur, I started using such a solution and it has worked fine for the last 6 years or so. Search on thermoswitch and find the relay solution before you go through the trouble of pulling the evaporator out and opening a can of worms.

 

Do you have a link to this discussion? I have never seen this discussed and have never found it on a search.

 

Here is one, I know that there are others:

https://www.rx7club.com/showthread.p...tch+relay+work

Keywords: thermoswitch, relay, work[around], etc..

 

[QUOTE=antony920;9467879]
Here are what i have done so far,


checked and add more Freon into the system


here's what I just noticed. unless you are an A/C tech, you couldn't have added freon to your system. if you are talking about the cans you get at an auto shop, like autozone or pepboys, those aren't freon, they're r-134. most of these cars came with R-12 (freon), and adding r-134, will lead to problems and is not recommended.

 

hum...but i read on this forum that people retro fit them all the time? i read and research this forum that they work so i though i gave it a try since r12 are so expensive now and days.

i have been driving for the last week with forcing grown to the relay switch so that the compressor turn on and it works great... AC get down to about 38-40 on freeway and 45 at stop light.

 

retrofit-yes, mixing-no. it will work fine for awhile, but the r-134/oil will eat away at the o-rings used in the r-12 systems, and they will eventually fail. and the oil used in r-12 systems will not suspend in the r-134. it will work fine if you retrofit it, meaning you pull a hard vacuum in the system and remove all the r-12 and then fill it with r-134. If you are worried about the cost, a product called Freeze-12 is out there that will work fine with a r-12 system and is much cheaper. the only problem is it takes a few minutes to get as cold as real r-12, but it will get just as cold.

 

just replaced the PowerFC with Factory ECU and the compressor turn on just fine... very interesting that it worked with power fc before

 

did you check under the FC sensor s/w menu to see if the A/C switch was coming on at any fan speed?

 

yes i checked that and it comes on, going to try to get a warrenty since i only bought it less than 30 days ago...

thanks everyone for your help