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'03 Merc. G. Marquis 3 Min. delay after A/C switched on.
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wayne77
Novice
May 28, 2010, 8:38 AM
Post #1 of 9
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'03 Merc. G. Marquis 3 Min. delay after A/C switched on.
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Dear Mechanic, Please help.
I've got a 2003 Mercury Grand Marquis, 4.6L, with standard (not digital) Air Conditioning.
When I turn it on it takes three minutes or longer before the compressor comes on to cool the car. There was no precipative event that caused this condition.
The fan does come on immediately and blows ambient temperature air.
I have a static pressure of 93 PSI, high pressure cycles between 200 PSI and 250 PSI, and low presssure cycles between 33 PSI and 50 PSI.
NEW EDIT: Last weekend there were at least three occasions when the A/C compressor shuddered when coming on, causing the serpentene belt and idler pully to jump. However, I'm not noticing this now. Two weeks ago I partial charged the system with 24 ounces of R-134a.
The radiator cooling fan does come on to cool the radiator at higher temperatures, as normal.
Wiggling the A/C control switch does not appear to have any effect on the compressor circuit.
The Ford Dealership Parts department representative said the Police car fleet mechanics buy five thermisters at a time to replace in their fleet cars. I wonder if this is a device that can cause a three minute delay in the compressor circuit.
As the compressor cycle switch does cycle between 33 PSI and 50 PSI, it doesn't seem to be the problem.
Being unfamilliar with this system, I am at a loss what (electrical) component could cause such a condition when performing abnormally.
What would be going on during these three minutes delay that, when that activity is complete, allows the system to turn on?
I have diagnosed a leaking evaporator core using a leak sniffer, and plan to replace it. The Tampa environment has lots of oak trees, allowing organic debris to accumulate in the bottom of the evaporator core chamber, the flapper drain valve seems to be clogged, and there is A/C oil on the bottom pipe of the evaporator core.
NEW EDIT: Also, this week I'm noticing a vibrating noise in the right dash area. I'm thinking this might be the blower fan encountering some oak tree debris.
Please help.
Thanks, Wayne.
(This post was edited by wayne77 on May 28, 2010, 10:02 AM)
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Hammer Time
Ultimate Carjunky
/ Moderator
May 28, 2010, 8:43 AM
Post #2 of 9
(2190 views)
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Re: '03 Merc. G. Marquis 3 Min. delay after A/C switched on.
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Since you have a manual A/C system and not automatic, I doubt you have a thermistor in the circuit. You may have a weak clutch on the compressor or a lazy relay. You will have to test for power at the compressor while the system is on but the compressor is not coming on to find out.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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wayne77
Novice
May 28, 2010, 9:52 AM
Post #3 of 9
(2184 views)
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Re: '03 Merc. G. Marquis 3 Min. delay after A/C switched on.
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Dear Hammer Time,
Thank you for your input.
I connected a voltmeter to the compressor connector and ran the engine with the A/C turned on. The voltage hovered at 0 Volts until 3-5 minutes when it registered full battery voltage, +12 Volts.
I forgot to mention previously that last weekend there were at least three occasions when the A/C compressor shuddered when coming on, causing the serpentene belt and idler pully to jump. However, I'm not noticing this now.
Also, this week I'm noticing a vibrating noise in the right dash area. I'm thinking this might be the blower fan encountering some oak tree debris.
Thanks, Wayne.
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Hammer Time
Ultimate Carjunky
/ Moderator
May 28, 2010, 10:41 AM
Post #4 of 9
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Re: '03 Merc. G. Marquis 3 Min. delay after A/C switched on.
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OK, that pretty much eliminates the compressor as being the problem. At this point your going to have to do some testing at the relay. The relay is controlled by the PCM through the trigger ground on the pink/yellow wire. When the PCM applies ground, that energizes the relay. What you need to find out is if that signal is being delayed or is the relay just slow in responding.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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wayne77
Novice
May 28, 2010, 1:08 PM
Post #5 of 9
(2178 views)
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Re: '03 Merc. G. Marquis 3 Min. delay after A/C switched on.
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Hammer Time,
I exchanged relays with the moonroof circuit (same relay part numbers) and there was only a minor 10 second delay. I am now waiting until it cools down to re-test and confirm this result.
I have verified this system does have a Thermister and I'm planning to replace it due to their poor service track record.
Wayne.
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Hammer Time
Ultimate Carjunky
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May 28, 2010, 1:15 PM
Post #6 of 9
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Re: '03 Merc. G. Marquis 3 Min. delay after A/C switched on.
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I don't know where your planning on putting that thermistor because there is none in the circuit. That is a temp sensor used for auto temp control. If your system is truly manual, it doesn't have one. If it's Auto Temp control, then it does.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Tom Greenleaf
Ultimate Carjunky
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May 30, 2010, 8:21 AM
Post #7 of 9
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Re: '03 Merc. G. Marquis 3 Min. delay after A/C switched on.
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Wayne77: Back to a first note you made....
">>Two weeks ago I partial charged the system with 24 ounces of R-134a.<<"
Holy smokes! That's most of the whole system's charge! Now with compressor complaining no wonder - it's choking on refrigerant IMO. You can't know how much is in the system by pressures only by filling from a vacuum. There are tons of safeguards to shut it down that can be confused by debris, RPMs and the ambient temps. Pressures looked good for a second there but at what RPM and conditions?
T
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wayne77
Novice
May 30, 2010, 8:13 PM
Post #8 of 9
(2152 views)
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Re: '03 Merc. G. Marquis 3 Min. delay after A/C switched on.
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Dear Gentlemen,
Thank you very much for your driven responses to this unique A/C problem.
This is the latest repair update.
I replaced the evaporator core, orifice tube, receiver/dryer, temperature sensor, and added 7 ounces of PAG oil and recharged the system. I also exchanged the compressor relay with the moonroof relay, as the part numbers are the same and there is no moonroof on this car.
Currently, after two days in service, the end result is that the system leak is repaired; the air conditioner is ice burg cold; and the compressor has resumed normal operation.
I greatly appreciate your technical advice and insight on this repair.
I was at that point in this repair that the possible unknowns were overwhelming, and I knew I needed to keep it simple. You gentlemen allowed me to do that, and for that I am deeply appreciative. I encourage you to keep on your current track as I find your trouble-shooting and problem-solving techniques to be very good and very fine.
Again, thank you.
Sincerely,
Wayne.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
May 31, 2010, 7:32 AM
Post #9 of 9
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Re: '03 Merc. G. Marquis 3 Min. delay after A/C switched on.
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Thanks for posting your fix. It's working so hard to argue with that now. Do use caution and keep track of oil amounts. 7oz is a fair amount to add for the parts replaced. Generally you would drain oil parts, and add that plus a couple. Hard to be exact as to where oil would settle so without all of it flushed out adding oil is educated guessing,
T
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