[holler1]

During recent hot weather, my ac would occasionally run warm. I didn't check the compressor at the time because I was trying to get a hard starting problem fixed (it is fixed now). In checking the AC out a few days later, I found that the AC was cold but the compressor would run almost all the time when the AC switch was on. The AC condenser cooling fan never came on at any time. The condenser gets pretty hot since it sits next to the radiator. I used a pressure gauge set and the pressures seemed pretty high. The pressure was about 70 psi with engine off. With engine running, low P was about 55 and high P about 300. Since the electric condenser fan was off, I figured the temperature in the condenser was pretty high. Next morning with engine cold, the pressure with engine off was 55; with engine running low P was around 25-45, high P was about 135-170. The compressor ran a very long time (minutes) after the low P came down to the 25-30 range, and only stayed off a few seconds when it did go off. I let the engine warm and the condenser fan never came on. The fan does come on when I short the light green wire on the pressure switch to ground, and that seems to make the compressor cycle more. I swapped the condenser fan relay for the AC relay, and that also seemed to make the compressor cycle more often (on 30-50 secs, off 15 secs). So the AC seems to be working most of the time now, but the condenser fan never comes on. According to a data table I found for the triple pressure switch, it is supposed to turn on the fan when the "medium pressure side" of the switch sees pressures increasing to 164-206 psi. I'm not sure what "medium pressure" means here and don't know how to check the switch. I'm also not sure what is controlling the compressor cycle, unless it is the evaporator temperature sensor. If there are any AC gurus who could help out, I would appreciate it. This isn't an urgent issue with the cooler weather, but I would like to get it working right.

 

[kevinjohnson3216]

Sounds like you should try jumping the pressure switch connector and if that turns the fan on then I would replace the pressure switch

 

[holler1]

Sounds like you should try jumping the pressure switch connector and if that turns the fan on then I would replace the pressure switch

Thanks for the comment. I did jump the pressure switch and the fan came on, but I don't know if the pressure in the system is in the range where the switch should turn it on. I would like to check that first if possible, since the system would have to be evacuated and refilled when changing the switch. I think you are probably right, though. If I cant figure it out soon, I'll probably wait til spring to change it and refill, since the AC wont be needed much until then.

 

[holler1]

As mentioned earlier, I don't understand the term 'medium pressure' in relation to the triple pressure switch. AC systems are usually described as having a high and low pressure side, but not medium pressure. The only thing I can think of is that it may be the pressure differential between high and low sides. If so, it seems that it would run between about 100 and 200 psi. Can anyone clear this up?

 

[kevinjohnson3216]

I think your pressure switch is no good - the wiring is definitely good because the fan came on when you jumped it

I don't think it's not coming on because of low refrigerant as your numbers don't sound like you have a low charge

 

[Cusser]

During recent hot weather...

Like the 110F in Phoenix yesterday ???

I think your pressure switch is no good - the wiring is definitely good because the fan came on when you jumped it.

I also agree that most likely this is related to the failure of the condenser fan to turn on. On many vehicles, such electric fan(s) run whenever the AC is switched on.

Since this is a 1st generation truck, try replacing that switch; I don't know on this truck, but on some one can replace such switch without losing refrigerant, there's a valve involved. If that doesn't help, consider running a toggle switch under the dash to that condenser fan and power that up manually to see if that is a workaround.

Note that my 2004 4-cylinder Frontier has a belt-driven fan so I can't give hands-on experience on this issue.

 

[Sabretooth]

With engine running, low P was about 55 and high P about 300
with engine running low P was around 25-45, high P was about 135-170

What were the ambient temps at time of these readings?

Your pressures don't say low maybe high side a little considering and I'm guessing here if the 110temp(as Cusser posted) is in afternoon and say 80's morning Id be in favor of the switch also
Remember temps are going to add pressure as the ambient temp goes up.
Here is the chart I've used in past
AC Pressure Chart | R-134a Temperature Pressure Chart

I lived in Gilbert how is it there now it's been 10yrs? I use to live off Higley near Guadalupe. You know after moving there and saying OMG why aint the car chillin it was because the heat just made the a/c work an work it couldn't keep up especially with the long windshields(to me acts like a magnifying glass) that they put in vehicles nowadays. The first thing I did was put heat rejection tint on my vehicles and the house Danny's Carousel in Scottsdale. Right now I'm using 3M Crystaline even on windshield as I still get heat here now that I live in Tx also just it's mixed with more humidity and what a difference it is worth the money I will always recommend it and your a/c will like you for it to not to forget your interior

Wanted to add you ever clean your evaporator n condenser check it out? see how gunked up the evap is under dash you might be amazed whats there

 

[Cusser]

I also agree that most likely this is related to the failure of the condenser fan to turn on. On many vehicles, such electric fan(s) run whenever the AC is switched on.

Since this is a 1st generation truck, try replacing that switch; I don't know on this truck, but on some one can replace such switch without losing refrigerant, there's a valve involved. If that doesn't help, consider running a toggle switch under the dash to that condenser fan and power that up manually to see if that is a workaround.

Note that my 2004 4-cylinder Frontier has a belt-driven fan so I can't give hands-on experience on this issue.

Thinking a bit more: the lack of the electric fan coming on will cause the condenser to be unable to shed enough heat, and the high side pressure will rise. I suspect that this is why the system is shutting off, has reached the pressure at which the system shuts down to prevent damage. I recently had similar issue on my 1998 Frontier (OK, that was a 120F day back in June) when my fan clutch was faulty so similarly could not cool the condenser; a new fan clutch solved that. Your electric fan does similar job to that fan clutch, to allow the hot refrigerant in the condenser to condense to a hot liquid, to it can draw in heat from the cabin and expand in the evaporator.

 

[holler1]

I think your pressure switch is no good - the wiring is definitely good because the fan came on when you jumped it

I don't think it's not coming on because of low refrigerant as your numbers don't sound like you have a low charge

Yes, I think the wiring and relay are good.
The only reason I'm not sure about the refrigerant level is that the low pressure comes down very fast when the compressor turns on.

 

[holler1]

Like the 110F in Phoenix yesterday ???


I also agree that most likely this is related to the failure of the condenser fan to turn on. On many vehicles, such electric fan(s) run whenever the AC is switched on.

Since this is a 1st generation truck, try replacing that switch; I don't know on this truck, but on some one can replace such switch without losing refrigerant, there's a valve involved. If that doesn't help, consider running a toggle switch under the dash to that condenser fan and power that up manually to see if that is a workaround.

Note that my 2004 4-cylinder Frontier has a belt-driven fan so I can't give hands-on experience on this issue.

Luckily, it never gets that hot here in Northern WV, but we do get the high humidity. My truck was very slow to start after getting hot and then sitting a while. It turned out to be a bad distributor. I had replaced the distributor last winter because of a bad miss, but the replacement also was faulty.

Good to know it might be possible to replace the pressure switch without having to refill. I'm going to order the switch and try that. If it doesn't work any better, I'll see if I can figure out how to rewire the pressure switch so it comes on whenever the AC is on.

My truck, a 1999 3.3l v6, has a belt-driven fan on the main radiator, but also the electric fan in front of the AC condenser.

 

[holler1]

With engine running, low P was about 55 and high P about 300
with engine running low P was around 25-45, high P was about 135-170

What were the ambient temps at time of these readings?

The first set was taken during a warm day with the engine fully warmed up. The temp under the hood was probably at least 90F, and as mentioned before the condenser fan was not running. The second set was taken in early morning at around 65F, with the engine cold, and the pressures match up pretty well with your chart. Thanks for that reference.

Wanted to add you ever clean your evaporator n condenser check it out? see how gunked up the evap is under dash you might be amazed whats there

No, haven't cleaned it. I've had the truck about a year (no excuse I know).

 

[holler1]

Thinking a bit more: the lack of the electric fan coming on will cause the condenser to be unable to shed enough heat, and the high side pressure will rise. I suspect that this is why the system is shutting off, has reached the pressure at which the system shuts down to prevent damage. I recently had similar issue on my 1998 Frontier (OK, that was a 120F day back in June) when my fan clutch was faulty so similarly could not cool the condenser; a new fan clutch solved that. Your electric fan does similar job to that fan clutch, to allow the hot refrigerant in the condenser to condense to a hot liquid, to it can draw in heat from the cabin and expand in the evaporator.

That's what I'm kinda guessing must have happened when I started getting warm air out of the vents. That only has happened a few times in hot weather (for us hot is above 90F or so). As far as I know the fan clutch on my mechanical fan is working since the engine is not overheating. On my code reader the ECT shows around 177F with the AC running, and the dash gauge sits at about the 3:30 pm level. The ECT is a little lower when the AC is off. As far as I can tell, the AC being on does not trigger the clutch on the mechanical fan or the electric fan on the condenser.

Just one other thought. I've had to add refrigerant to the AC on a couple of other vehicles, and with those low refrigerant causes the compressor to go into a fast cycle; a few seconds on and a few seconds off. When refilled, the cycle gets longer, coming on for maybe 20 seconds or so. Also the electric fan would turn on regularly. This one doesn't seem to work the same way.

 

[Sabretooth]

The first set was taken during a warm day with the engine fully warmed up. The temp under the hood was probably at least 90F, and as mentioned before the condenser fan was not running. The second set was taken in early morning at around 65F, with the engine cold, and the pressures match up pretty well with your chart. Thanks for that reference.

Always measure after it is warmed an a/c is blowing do it with the chart that you've got some sort of a baseline to go from


No, haven't cleaned it. I've had the truck about a year (no excuse I know).

Holler1 I haven't done mine either lol I just ask because it cant hurt it don't cost anything but some of your time. How is the air when flying up the 101 is it good? Since you don't have any history I'd split the condenser from the radiator have a feeling it'll be plugged up with debris.

 

[kevinjohnson3216]

Just had some food for thought for you:

Most 1st gens don't come with an additional electric fan for cooling the AC condenser. My 01 v6 doesn't have one

 

[Cusser]

As far as I know the fan clutch on my mechanical fan is working since the engine is not overheating.

That's not necessarily a reality. My 1998 Frontier never ran hot, even in June's 121F day, when its fan clutch was bad. Pointer never varied from its typical 1/4 way up the gauge. But my AC pressures were way too high before I installed the new fan clutch.

I could visually see my fan spinning too slow, and confirmed its condition using the rolled up newspaper technique (it stopped the fan). Read up on fan clutch diagnosis on the Internet. Typically, a vehicle with a bad fan clutch will run hotter in traffic and be OK on the highway, but AC seems to be more picky about a good fan clutch. On my 1988 Mazda truck (mine since 1994), I typically have to swap out its fan clutch every 6 years here in Arizona (108F yesterday).

 

[kevinjohnson3216]

That's not necessarily a reality. My 1998 Frontier never ran hot, even in June's 121F day, when its fan clutch was bad. Pointer never varied from its typical 1/4 way up the gauge. But my AC pressures were way too high before I installed the new fan clutch.

I could visually see my fan spinning too slow, and confirmed its condition using the rolled up newspaper technique (it stopped the fan). Read up on fan clutch diagnosis on the Internet. Typically, a vehicle with a bad fan clutch will run hotter in traffic and be OK on the highway, but AC seems to be more picky about a good fan clutch. On my 1988 Mazda truck (mine since 1994), I typically have to swap out its fan clutch every 6 years here in Arizona (108F yesterday).

So let me get this straight - at 121F outside temp your coolant temp gauge reads 1/4? Assuming that coolant is about 190F

Mine reads 1/2 at 170-190F (my operating temp with a warmed up engine at 80F outside temp

 

[holler1]

That's not necessarily a reality. My 1998 Frontier never ran hot, even in June's 121F day, when its fan clutch was bad. Pointer never varied from its typical 1/4 way up the gauge. But my AC pressures were way too high before I installed the new fan clutch.



I could visually see my fan spinning too slow, and confirmed its condition using the rolled up newspaper technique (it stopped the fan). Read up on fan clutch diagnosis on the Internet. Typically, a vehicle with a bad fan clutch will run hotter in traffic and be OK on the highway, but AC seems to be more picky about a good fan clutch. On my 1988 Mazda truck (mine since 1994), I typically have to swap out its fan clutch every 6 years here in Arizona (108F yesterday).

Very interesting. I've read a little about that but I'm not sure I've checked the fan clutch when the engine is really hot. I did check to make sure it had some resistance to turning when the engine is off. I'll look into that.