[vzfox]

So the a/c was working great, thought I had it fixed then suddenly on the way home it started blowing warm air. I got home and checked the pressure on the low side....it showed way too high at near 75 psi and the line was warm to the touch (low side). The high side is hot to the touch. I pulled the cover for the relays under the hood and seen the a/c com relay was steadily "clicking". The a/c clutch wasnt turning. I pulled the relay and jumped the a/c clutch wire to force the compressor to run. The low line started getting cold and the air inside was blowing nice and cold again. But if I pull the jumper wire and plug the relay back in, it just clicks steadily and the a/c clutch will not turn.

Ambient temp outside is near 90 degrees (very humid) and the vehicle temp is up to temp (normal operating temp).

Why can I jump the a/c clutch wires and have it blow nice and cold but the relay will not let it come on? Why does the low pressure line have such high psi pressure once the vehicle gets to normal operating tempature?

 

[vzfox]

Here is what I found thus far......while running a continuity test on the triple pressure switch, the truck was running and a/c was on. I was testing cont between terminals 3 & 4 when suddenly the condensor fan came on. The a/c clutch kicked in and the a/c started blowing cold. I let it run for a couple minutes, then pushed the button and turned the a/c off. After a couple minutes I turned it back on....no cold a/c and condensor fan would not come on again. I thought maybe it had something to do with the triple pressure switch testing I was doing so I tapped on the switch to see if the fan would come back on....it would not.

Do you think it could be the relay for the condensor fan? When is the fan suppose to come on?

 

[vzfox]

Here is what I found thus far......while running a continuity test on the triple pressure switch, the truck was running and a/c was on. I was testing cont between terminals 3 & 4 when suddenly the condensor fan came on. The a/c clutch kicked in and the a/c started blowing cold. I let it run for a couple minutes, then pushed the button and turned the a/c off. After a couple minutes I turned it back on....no cold a/c and condensor fan would not come on again. I thought maybe it had something to do with the triple pressure switch testing I was doing so I tapped on the switch to see if the fan would come back on....it would not.

Do you think it could be the relay for the condensor fan? When is the fan suppose to come on?

Well, im at a loss for whats going on.....I let the truck cool for about 45 mins and went and restarted it and turned on a/c. Blows cold, condensor fan is on and a/c clutch is going. I turned the a/c on and off a few times, let the truck get to operating temp again and even tapped fairly hard on the 4 pin relay, condensor fan ran as it should and so did the a/c clutch both kicking on and off every few mins. I have no idea whats going on here, sometimes it works without flaw and other times it wont blow cold to save your life.

All the tests that the book shows to run for voltage and cont for the triple pressure switch, 5 pin a/c com relay and the 4 pin cond fan relay all test good. Obviously an intermitten problem that I cant seem to hunt down.

All suggestions at this point are welcome......

 

[johnnie59]

Sounds to me like a bad relay. Try changing it with one of the others that are the same and see what happens. If the trouble moves to the new circuit then you'll know for sure its the relay.

 

[isuzu95]

I wonder if you have overcharged the system?

 

[vzfox]

Well, I thought it was a relay also so I switched the connections with the one next to it which is the exact same. I didnt change anything. It tested good according to the book cont testing.

As for overcharging the system, that might be a possiblity. But doesnt logic state that if the system is overcharged or undercharged, the a/c will either work or not. Doesnt make sense that it would work fine for a few hours one day and not at all the next. I did try to purge the low side of freon to lower the pressure but I couldnt get the a/c to come on at all again, so I put a can back in it. It still acts the same, working sometimes but sometimes not. I did get the low side pressure to read about 50 psi now, but if I lower it any more the compressor and cond fan wont kick on at all.

 

[vzfox]

More of an update....tested it again today, blows nice and cold but I noticed the pressure for the first 15 mins or so was around 45 psi at idle and would drop to around 35 psi at 2k rpm. After it got to operating temp I noticed the pressure (low side) shoot up to about 75 psi and didnt want to come back down no matter how high the rpm's were. The clutch kept turning, the cond fan kept turning and the a/c inside still blew nice and cold.

Is the pressure suppose to flutuate that much and get so high at operating temp?