AC blows cold when truck moving, warm when idle

[TrexMex]

high or low.. with the engine off.. a properly charged system will be about 10-20 PSI above outside TEMPERATURE.

if you're pressures are ok and it only cools while in motion, you have a problem with your cooling fan. or the outside temperture is too high for the cooling fan to work efficiently

Noticing engine is temp is high when idling, I'm afraid this might be deeper than just not enough/too much AC system charge. I'll have to fix the high engine temp issue first and then come back to this problem.. Thanks for all the help so far, I'll keep you posted.

 

[BRUTUS_T_HOG]

well in 100 degree weather the engine is not going to cool very well.. especially with the a/c on.. and a BAD fan!

how hot are we talking here?

 

[TrexMex]

well in 100 degree weather the engine is not going to cool very well.. especially with the a/c on.. and a BAD fan!

how hot are we talking here?

How 'bout 122 ?? Fan clutch is 3 weeks old BTW

 

[BRUTUS_T_HOG]

122 degrees outside temp the best you're going to see out of the vents is about 30-50 degrees below outside temp..

you might not even have a problem at all. r-134a systems dont perform well in very hot weather..

in fact the minimum cooling that a fully functional r-134a system is supposed to do is 30 degrees below outside temp.

 

[KurtC]

in fact the minimum cooling that a fully functional r-134a system is supposed to do is 30 degrees below outside temp.

If it's not on recirculate, that's ture. If on max, it'll keep cooling the cab down and the vent temp will depend on the air temp being pulled from the cab. Mine will get down to 39 vent temp on the freeway even on a 100 degree day.

 

[TrexMex]

I guess because the condenser is being hit by high temp air it wouldn't be so efficient, so to add to your point maybe increasing air flow? A friend of mine mentioned he put an "auxiliary" manual actuated electric fan in front of the condenser, whenever thigs get to hot, he just turns the thing on and that helps the ac and the engine temp go down a notch while idling....

Has anyone tried this approach?

 

[BRUTUS_T_HOG]

If it's not on recirculate, that's ture. If on max, it'll keep cooling the cab down and the vent temp will depend on the air temp being pulled from the cab. Mine will get down to 39 vent temp on the freeway even on a 100 degree day.

A/C performance is DEPENDENT on airflow across the condenser. your 1990 could have R-12 or R-134a. R-12 is a much better performing refrigerant

but at freeway speeds most a/c systems will perform well in hot weather but we are talking about at a stoplight it blows warm and then gets colder with speed.

 

[KurtC]

I guess because the condenser is being hit by high temp air it wouldn't be so efficient, so to add to your point maybe increasing air flow? A friend of mine mentioned he put an "auxiliary" manual actuated electric fan in front of the condenser, whenever thigs get to hot, he just turns the thing on and that helps the ac and the engine temp go down a notch while idling....

Has anyone tried this approach?

An electric fan will absolutely help when idling. With the engine at idle, the fan clutch just isn't going to pull much air through the condenser. A well designed electric fan system would work much better, however, implementing an efficient system (like the OEM does on Hondas, ect.) will be a lot of work. A decent system would involve removing the stock fan clutch, finding a shroud/fan combo that would fit over your stock radiator, and devising a control system to opperate the fan based on a few parameters. Not simple and certainly not cheap.

Bolting an extra fan to push air through the condenser with a simple on/off switch might get you a little better performance at idle. It would just depend on how much air it would flow through it. That would depend on how you've mounted the fan and closed the gap between it and the condenser.

A/C performance is DEPENDENT on airflow across the condenser. your 1990 could have R-12 or R-134a. R-12 is a much better performing refrigerant

but at freeway speeds most a/c systems will perform well in hot weather but we are talking about at a stoplight it blows warm and then gets colder with speed.

It's a retrofit, 134a. There's more to it than just that. Good a/c performance is dependent on pulling heat from the cab and putting it outside. Air going over the condenser is certainly a big part of that. It'll start out at about 30 degree cooler temp, but as the air entering the evaporator gets cooler (cab cools down), the air exiting it (vent temp) will be that much cooler, so there's a time factor. This is assuming a healthy a/c system, of course!

With the fan clutch, it's pretty much assured vent temps will rise at idle in very hot weather. I was making the point that the air temp in the cab will make a difference in vent temp, which could be much more than 30 degrees below ambient.

 

[BRUTUS_T_HOG]

An electric fan will absolutely help when idling. With the engine at idle, the fan clutch just isn't going to pull much air through the condenser. A well designed electric fan system would work much better, however, implementing an efficient system (like the OEM does on Hondas, ect.) will be a lot of work. A decent system would involve removing the stock fan clutch, finding a shroud/fan combo that would fit over your stock radiator, and devising a control system to opperate the fan based on a few parameters. Not simple and certainly not cheap.

Bolting an extra fan to push air through the condenser with a simple on/off switch might get you a little better performance at idle. It would just depend on how much air it would flow through it. That would depend on how you've mounted the fan and closed the gap between it and the condenser.





It's a retrofit, 134a. There's more to it than just that. Good a/c performance is dependent on pulling heat from the cab and putting it outside. Air going over the condenser is certainly a big part of that. It'll start out at about 30 degree cooler temp, but as the air entering the evaporator gets cooler (cab cools down), the air exiting it (vent temp) will be that much cooler, so there's a time factor. This is assuming a healthy a/c system, of course!

With the fan clutch, it's pretty much assured vent temps will rise at idle in very hot weather. I was making the point that the air temp in the cab will make a difference in vent temp, which could be much more than 30 degrees below ambient.

HEAT is absorbed by the refrigerant from the air in the cab by the evaporator... then the HEAT that is removed from the cab is REMOVED from the refrigerant by the CONDENSER. yes putting it on recirculate makes it colder because there is less heat load each time it recirculates it removes more heat. heat moves from an area of more heat to less heat.

so as i said A/C performance is dependent on airflow across the condenser to REMOVE heat. im not saying your wrong or anything. im just saying that you can't get have cold a/c without heat being removed by the condenser.

and when i said 30 degrees minimum i was referring to an industry standard for a/c repair.. its basicly just a reference to go by saying that a properly working a/c system should be able put out at least 30 degrees below ambient temp if not more.

did you do a retrofit to reduce cost of recharge?

 

[KurtC]

Yeah, didn't want to spend a lot of money on R12! System was completely disconnected when I bought the truck, so it was not much of a decision.

 

[BRUTUS_T_HOG]

does it cool good? i can recharge my R-12 myself for about $50 at work but have also been looking at retrofitting

 

[KurtC]

Yeah, it's pretty good. Just cruising around town at 30-45mph, it'll cool down to in the 40s vent temp. If you retrofit, flush all the old oil out and put 12oz PAG or Ester oil back in, 6oz in compressor and other 6 into the accumulator, evaporator and condenser. You have to add ester oil with the retrofit and with all the extra oil, performance suffers, so it's best to flush and put the correct amount in.

 

[TrexMex]

Well I don't have have the problem anymore, simply because I don't have A/C anymore Compressor went to the crapper last saturday so now it's pretty much replacing condenser, compressor, expansion valve, accumulator and God knows what else.... Should I be looking at replacing the evap as well?

I'm naming this truck "the can of worms".....

 

[TrexMex]

Anyone on what can I keep and what needs to go to do a complete "overhaul" on my AC system?

Any help will be greatly appreciated

 

[4x4junkie]

Well, I hust had a whole page typed out here and lost the whole fing thing because the page somehow reloaded and cleared my whole box out :

Your '94 had eirther R-12 or R-134a depending on it's production date. If you find any black goo in there (Black Death),you'll need to change at minimum: compressor, condenser and orifice tube. Make sure all the lines and hoses are thoroughly flushed out as well (if the evaporater doesn't come clean in one flush, I suggest replacing that as well. Any debris in the system will quickly cause the new compressor to fail as well.