P30 Electric Fan question

[69Stang]

Originally Posted by Lifemember

I bypassed the switches and installed a switch on the dash. I run the fan when driving in town or at idol. Here is a link to the P30 chassis manual for motorhomes



http://www.gmcmi.com/wp-content/uplo...sis-Manual.pdf

Thanks again

[Mudfrog]

Originally Posted by 69Stang

Thanks Lifemember. So it is normal for the electric fan not to run until the system pressure reaches 225 PSI of refrigerant pressure. I watched the fan while the DW ran the idle up to about 2K, but the engine driven fan is sucking air and spinning the electric fan so I can't tell if it's working or not.

Anyone know of a way to test the pressure switch?

Put a gauge on the high side and see what the pressure is. If the fan doesn't come on when pressure goes much above 225 lbs, then suspect that it may not be working. If pressure doesn't reach the 225 mark, then you might try holding a piece of cardboard or something similar in front of the condenser coil to block off some of the airflow for a bit. The pressure should come up pretty quickly. Just be sure to not cause an overheating situation by blocking for too long.

[69Stang]

Mudfrog, thanks for the suggestion. I'll have to find someone with gauges to give that a try.

[lonfu]

Originally Posted by Lifemember

The A/C system has a temperature switch (NORMALLY OPEN.,CLOSES TO GROUND
AT 221 °F APPROX.)

also an A/C pressure switch (NORMALLY OPEN .CLOSES TO GROUND AT 225 PSI .
REFRIGERANT PRESSURE)

This is what makes the fan run.

In CAPS. is information taken from repair Manuel.

On a 1998 P30 chassis, the exact chassis I have, the fan relay closes when the AC is turned on. When I was chasing down the electrical open in my compressor clutch circuit, I found the relay for the fan only turns on when the AC is activated, not when the high pressure switch closes. It stays on all the time until the AC is turned off. I can't say about other years as I've not tested them personally.

As I mentioned before, I found that when this fan is activated the coolant temp (mechanical gage), the transmission temp (mechanical gage) and the engine head temp (electric gage) all rise...... This is because the electric fan cools the mechanical fan clutch and reduces the volume of air drawn through the condenser and radiator. i have also found that the inside AC temp rises from 42 degrees to 52 degrees.

My original factory 4 volume service was wrong about this. I have found that over the last 19 years of servicing this chassis that there are little mistakes in the manual. What else can I say! What the book says is one thing, what the gages say is another.

[lonfu]

One last thing, if your P-30 chassis is running hotter than 200 degrees, driving flat terrain, 80 degrees ambient, YOU HAVE A COOLING PROBLEM!

When you are pulling up a grade, your fan clutch should be roaring and it should not go over 210 degrees, EVER! If you choose to be lazy and not take care of the problem, then don't be surprised when your tranny fails.

Transmissions are not designed to run at 210 degrees. They are designed to run at 160 t 180 degree's. That is why the tranny coolant tank is at the bottom of the radiator where the coolant is coolest. Most p30 chassis come with an external transmission cooler/small tranny radiator to attempt to keep the tranny fluid in the correct temperature range. If your engine temp is at 220 degrees when going up a hill your tranny temp will be higher than the specs and cause premature tranny wear and fail early. Most of the tranny failures that I have rebuilt have been due to burned bands and clutch plates.

So, in a 1998 P30 chassis, to control the tranny temp, use a 180 degree thermostat. since it doesn't fully open until 195 your rig will pass smog and your gas mileage will not suffer. I have checked this with my laptop computer and diagnostic software with a onboard computer connection. The loop closes at about 185 +or- 2 degrees. For you non computer fellas, this means that your gas mileage won't suffer unless you are touring Antarctica!

But that is another discussion about cold weather and how to keep your engine warm..... cardboard in front of the radiator and an electric oil warmer dipstick which you would need even with the 195 thermostat...

Facts: 180 thermostat begins to open at 180 but not fully open until 195
195 thermostat begins to open at 195 but not fully open until 210

Why you ask? the engineers have tried to install an all weather thermostat. Got to remember that these units are sold all over the world, altitudes and climates. The question financial management asks an engineer is, "what thermostat can we uses that will work best over all in all applications?". Duh, it is the 195, so they only have to purchase one temp stat for the manufacturing process. BUT, many of us do not live in Alaska.....

[kennyrodgers]

A bit different but related....
I recently fitted a 180° T/stat along with a severe duty Hayden fan clutch. Now my temps are up and down like a brides' nightie, temps go up...fan kicks in, temps go up...fan kicks in. This is constant, every two to three minutes.
I've been advised on another forum that one is fighting the other and to go back to the standard t/stat. Gonna try that and see what happens.
PS, my temps were fine before hand, I just thought I'd give the old girl some help.

[CJ7365]

Originally Posted by kennyrodgers

A bit different but related....
I recently fitted a 180° T/stat along with a severe duty Hayden fan clutch. Now my temps are up and down like a brides' nightie, temps go up...fan kicks in, temps go up...fan kicks in. This is constant, every two to three minutes.
I've been advised on another forum that one is fighting the other and to go back to the standard t/stat. Gonna try that and see what happens.
PS, my temps were fine before hand, I just thought I'd give the old girl some help.

Yup put it back to how it is suppose to be, in my opinion, messing with the T-stat serves no real help, plenty of RVs out there running the OEM t stat with no problems

I live in the Desert Southwest, I have the 8.1, stock 195 t-stat, just returned from a 1300 mile round trip, with outside temps in the high 90's, ran like a champ.

[lonfu]

Originally Posted by kennyrodgers

A bit different but related....
I recently fitted a 180° T/stat along with a severe duty Hayden fan clutch. Now my temps are up and down like a brides' nightie, temps go up...fan kicks in, temps go up...fan kicks in. This is constant, every two to three minutes.
I've been advised on another forum that one is fighting the other and to go back to the standard t/stat. Gonna try that and see what happens.
PS, my temps were fine before hand, I just thought I'd give the old girl some help.

As I mentioned before. When I replaced my fan clutch, I bought one from AZ and it failed, then I bought one from Napa (Hayden) and it failed. Went back to AZ got a replacement, a different style, and it works. got another Hayden from napa as a back up. That totals 2 failed fan clutchs to get one that works correctly. Sounds like you have a bad fan clutch. I'd take it back because the fan clutch cycling has nothing to do with the thermostat.

[udid]

Originally Posted by lonfu

One last thing, if your P-30 chassis is running hotter than 200 degrees, driving flat terrain, 80 degrees ambient, YOU HAVE A COOLING PROBLEM!

When you are pulling up a grade, your fan clutch should be roaring and it should not go over 210 degrees, EVER! If you choose to be lazy and not take care of the problem, then don't be surprised when your tranny fails.

Transmissions are not designed to run at 210 degrees. They are designed to run at 160 t 180 degree's. That is why the tranny coolant tank is at the bottom of the radiator where the coolant is coolest. Most p30 chassis come with an external transmission cooler/small tranny radiator to attempt to keep the tranny fluid in the correct temperature range. If your engine temp is at 220 degrees when going up a hill your tranny temp will be higher than the specs and cause premature tranny wear and fail early. Most of the tranny failures that I have rebuilt have been due to burned bands and clutch plates.

So, in a 1998 P30 chassis, to control the tranny temp, use a 180 degree thermostat. since it doesn't fully open until 195 your rig will pass smog and your gas mileage will not suffer. I have checked this with my laptop computer and diagnostic software with a onboard computer connection. The loop closes at about 185 +or- 2 degrees. For you non computer fellas, this means that your gas mileage won't suffer unless you are touring Antarctica!

But that is another discussion about cold weather and how to keep your engine warm..... cardboard in front of the radiator and an electric oil warmer dipstick which you would need even with the 195 thermostat...

Facts: 180 thermostat begins to open at 180 but not fully open until 195
195 thermostat begins to open at 195 but not fully open until 210

Why you ask? the engineers have tried to install an all weather thermostat. Got to remember that these units are sold all over the world, altitudes and climates. The question financial management asks an engineer is, "what thermostat can we uses that will work best over all in all applications?". Duh, it is the 195, so they only have to purchase one temp stat for the manufacturing process. BUT, many of us do not live in Alaska.....

Except that the dash gauge is anything but accurate for P-30 chassis(manual mentions this). The stock dash gauge will and does routinely go over 210 (normal behavior for the P-30)

[George Schweikle]

Correct that P-30 dash gauge is very inaccurate. A ScanGuage will report the real temperature as seen at the CPU.

Originally Posted by udidwht

Except that the dash gauge is anything but accurate for P-30 chassis(manual mentions this). The stock dash gauge will and does routinely go over 210 (normal behavior for the P-30)

[lonfu]

the dash gage works but you have to remember that it is "in" the head, not the coolant itself so it is much slower to respond to temp changes. I have a mechanical gage that is immersed in the engine coolant. It varies more in temp than the electric dash gage that is in the head. The dash gage always follows the coolant temp. My tech2 scanner reads the same as my mechanical gage, so clearly that sensor is immersed in coolant. Again the 180 degree thermostat will close the loop to allow the computer to adjust the fuel injector pulse width. I have found that the 160 thermostat will not close the loop without modifying the computer programming, so do not recommend it.

[udid]

Originally Posted by 69Stang

OK, so I took it to a local mechanic who ended up replacing the compressor, dryer, etc. I mentioned to him that the fan was also not coming on when the A/C was on. He said it won't come on until it reaches a certain head pressure and it won't do that until the A/C is working. So I had the repairs done and the A/C works great. I completely forgot about checking the fan until a week after the repair. I checked it a couple days ago and the fan still doesn't come on while idling with the A/C running. I also checked the fan by applying 12V and it works, it's just no power to it with the A/C running.

I just called and talked to the mechanic again and he assured me that everything was working correctly. The guy seems very knowledgeable and honest, I just want to make sure everything works as it should. Does his explanation sound legit?

From Chevy P30 Motorhome chassis service guide https://www.gmcmi.com/wp-content/upl...sis-Manual.pdf

Under Appendix 2-1 Optional Air Conditioning System...(Figure A2-1-7 Typical ARA Wiring Diagram - Class "A" RV Condenser with Fans) p.2-12

It shows the temp sender switch is normally open, closes to ground at 221F approximately.

NOTE: Starting with the 1991 Class A motorhome, the A/C condenser fan is wired by Chevrolet through the main front end engine wiring harness . The coolant temperature switch is now located in the RH cylinder head with a green wire.


It appears that the electric fan on the front of the A/C condenser should only come on after the relay closes (approx 221F) with the A/C on.

[udid]

Update:



This system is set up to turn the fan on when either of the conditions are met:


1. A/C off engine reaches ~220 fan kicks on


2. A/C on fan will turn on regardless of engine temp.


It's primarily intended to help draw more air into the condenser then onto the radiator during idling, traffic (stop & go situations). These RV setups have a rather large A/C condenser that sets right smack dab in front of the radiator. Because of that the engine temp can get rather high without the added fan to draw air thru the system when in traffic or prolonged idling situations. The metallic coil on the front of the mechanical clutch fan needs to have some air pushing on it to get an accurate reading. With that A/C condenser sitting where it is the engine fan alone (clutch not engaged) in traffic or extended idling is not enough to give the clutch fan coil enough flow thru air to get the clutch fan to engage. This is due to the fact that the coil sits directly on the front of the fan forward of the discharge side. With no fan or an inoperable one on the A/C condenser the radiator is heavily restricted from receiving air.

[69Stang]

Mine still doesn't turn on when the A/C is running. A/C works really well though.


I'm not even sure it would turn on at 220.