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Rebuilt truck a/c not cooling as it should. Robert 7-31-02  
We recently bought an '85 Winnebago Elandan 32' Class A. It's built on a Chevy P30 chasis with a 454 engine. The a/c hoses were disconnected when we bought it. They were all corroded inside. We took it to the local Goodyear a/c service center, and they converted it over to a R134 system. Everything (hoses, compressor, accumulator-drier, expansion valve, and even added an electric fan to further help cool the condensor) was replaced except the condensor which was still good. They flushed the entire system and checked all air ducts and routing.

The problem is that the air coming out of the vents is still not as cold as it should be. Running at Max with the fan on high, it feels more like having it on low when compared to my '94 Suburban; the air is cool but not cold. This is OK as long as I stay at the coast, but going inland at 100+ degrees, this can get uncomfortable.

According to the Goodyear guys, the system is functioning as it should. The lines (?) in the air box (?) is freezing/icing up, but the air coming from the vents is only 45-50 degrees. They said they have tried everything, but it might just be a flaw in the blower's design. They said that the way the blower is set up, it's pulling the cold air through (thereby warming it as it passes through the blower fan), rather than pushing it. I feel that they are sincere and honest with their work, but this does not solve the problem with the a/c. Is there anything else that can be done? Or, is this common with older Winnebagos? Any advice or suggestions will be appreciated.
Re: Rebuilt truck a/c not cooling as it should. Mallie 11-22-02  
Hello Robert, there is not enough info to properly diagnose with any degree of accuracy, but on site it not a problem for anyone with basic AC knowledge. If your AC folk can't tell you what the problem is, get another shop. There is a limit to what any AC can do, but it does not sound like your system is not performing within the designed limits.
As mentioned, you are going to have a specific temperature drop from the inlet evaporator air to the temperature of the air coming out of the ducts, based on conditions. Just duct temp is really not very useful alone.
Ask you AC expert what the super heat is, and the suction pressure, head pressure, cabin temperature and ambient temperature of entering condenser air.
Assuming the condenser is getting sufficient circulation, you can narrow it down real quick. A check of high pressure saturate temperature, and the sub cooing will tell that too.

If you have low suction, and high head, high super heat, it is a restriction, probably metering device or filter. If you have the same pressure combination, and low super heat, it is air restriction. If it is low head and low suction, and high super heat, low charge. You did mention freezing, and this can not happen if the suction pressure is above freezing on the Pressure/temperature scale.

First guess, Freezing, low suction, By the system being open, I would suspect the possibly of a restriction. If it is a cap tube, usually pretty easy to get to and check. The low suction pressure should have a low cut out, anyway. I think it is supposed to be changed on some conversions. Low charge can also cause this.

Second guess, The water is circulating in the heater radiator. Clamp it off by folding it and applying a spring clamp.

Third Guess, There should be a means to allow outside air into the system normally, but should provide a way to only return inside air, usually marked as max, or recalculate on the controls. If you are cooling the at high temperatures, you want to recalculate the inside air, instead of outside. Big difference.
Mallie
Re: Rebuilt truck a/c not cooling as it should. Joe 7-31-02  
It sounds like to me that you never had this air working before you had it repaired, so you have nothing to compare it to. First, 45-50 degree air out of a R12 converted to 134A system is about all you can expect. We do conversions constantly and I have yet to see a system that has been converted from R12 to 134A work quite as well as it did before, but it still should produce satisfactory results. Without knowing what the high and low pressures are it's hard to tell if the system is working properly.I would suspect there is possibly an air flow problem. When you said it felt like it was on low that leads me to believe it may have the wrong fan or there is something like an accumilation of leaves or a mouse nest buildup on the far side of the evaporater. Get a name off the unit and any info you can get to see if it has the right parts in it. Yours may be an "Evans" or a "Vern Air" system, in any case, many of the systems draw air through the Evaporator and work just fine. See if there is a make and model tag somewhere on it.
Re: Rebuilt truck a/c not cooling as it should. Sam Watson 8-1-02  
As Joe says, the AC was sized for a truck cab. AC's have a rating system, either expressed as BTU/H, which is merely the number of British Thermal Units removed per hour, or a refrigerent ton rating, equivalent to the amount of cooling of one ton of ice, or as it is used today, 12,000 BTUs removed per hour. Also, bear in mind that that AC cooling action is not consistant, but is usually expressed in the number of degrees drop in ambivant air temp at a given humidity factor. Let's pick a number such as ambient air temp of 70 degrees and 70% humidity. Using a 35 degree drop, then discharge air from your AC would be 35 degrees. Now lets take an ambivent air temp of 105 degrees, discharge air is now 70 degrees. Humidity enters into this also. To decrease humidity in "conditioned" air, incoming air is also passed through the heater core to help"dry" it out, as well as passed through the evaporater to cool it. Dry, cooled air "seems" cooler than it is because it uses our body's own cooling system---sweat evaporation---to aid it in the cooling effect. Given all this, you can see why presumeably your one ton rated dash air isn't going to treat all those cubic feet of air inside the rig, that takes both the 13,500 BTU roof AC's. BTW, "MAX" air setting is only 100% recirculated air, with no outside air admitted.
Re: Rebuilt truck a/c not cooling as it should. Joe 8-1-02  
Sam brought up a good point. Today as I drove down the road the temperature outside was 102. The air coming out of the air vents on my new 2002 Avalanche was a whopping 68 degrees, but it felt very comfortable in there.
Re: Rebuilt truck a/c not cooling as it should. Robert 7-31-02  
Joe, thanks. I will call the Goodyear shop and ask them for some of the info; i.e. pressure readings, parts manufacturers, etc. I will check on it myself as well.

In terms of the fan, when I have the fan on high, it does blow air through the vents at a high rate, and the Goodyear guys said that they'd checked all the ducts for obstruction, and found none. Therefore, I don't believe that the ducts are clogged. When I said that it felt as if it was on low, I meant that as comparing the cooling feel to my Suburban - that when I put the Suburban's a/c at a low setting. The RV's a/c just doesn't seem all that cold, especially when it's running at Max setting with the fan at high.

I can't remember exactly, but they said that the temp reading at the evaporator was something around or below zero, and the tubes were icing up. But for some reason they just couldn't get the air temp at the vents to get below 45.
Re: Rebuilt truck a/c not cooling as it should. Joe 7-31-02  
Is it possible that it may be drawing air from somewhere else than through the evaporater? Those temperatures seem normal. Freezing up is an indication that not enough air is passing through the evaporater or too much humidity, or the expansion valve tube isn't sensing the coldness of the evaporater. The other thing is that the "Truck" A/C will not cool the entire motorhome. Some motorhomes have a curtain that you draw closed behind you to keep the cold air in the drivers compartment cool so if you don't want to run the generator and the roof air you will still be cool.
Re: Rebuilt truck a/c not cooling as it should. Parker 8-3-02  
Fact is that systems designed for R-12 will never work as well with R-134a.
Systems designed for R134a cool because the system is designed for a lower boiling point coolant, R-134a.
Systems designed for R-12, if not converted can use Freeze 12 and work better.
Re: Rebuilt truck a/c not cooling as it should. Sam Watson 8-4-02  
That's right, a conversion from R 12 to R 134 can result in a 3-15% efficiency drop.
Re: Rebuilt truck a/c not cooling as it should. Rob 9-9-02  
I have just got a '84 winnebago with
a wierd problem like that.the a/c seems
to work fine (may need a little bump
of r-12) but when in drive the high
fan speed stoppes at about 2500rpm
then comes back on when it gets below this (engine rpm).this is true for all
selections(a/c,max a/c,heat,vent,etc.)
it does not do this in park,only drive.You
can be driving along @ 55mph with a/c
on high with only the lowest fan speed
on (the one that is designed to run when
the fan is turned off but a air selection is on) release your foot off
the gas and the high speed will kick in.
any clues??
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