Air Conditioning - Blower cuts off when compressor cuts on

I've got a 2 stage heat pump electrical AC home unit with digital thermostat.

The blower won't cut on when the compressor is on. When the compressor is off, the blower will cut on. Crazy.

I've replaced the thermostat and it does the same thing. I have a 2 stage heat pump approved Tstat. The previous Tstat has worked fine for the past year or so, so I don't think it is the thermostat.

Any suggestions?

If it was a something to do with the blower - capacitor or relay, surely it wouldn't cut on when the compressor was off?

It seems like the fan has got it's on and off confused. It is going off when it should be on and vice versa. I've left both breakers off for 1 hour to reset the capacitors or whatever, but it is still acting the same.

HELP! It's 94 F in the house now. Good for a sauna, not good for a happy wife.... :)

Assuming the compressor runs on 240v and the fan runs on 120v, there is a bad connection in the 120v line supplying the fan, and the compressor current runs through this same bad connection, therefore reducing the available voltage to the fan.

Assuming a 1 ohm bad connection, 30A compressor current draw and 2A fan current draw, when the compressor is on it sees 208v and starts anyway. When the compressor is on the fan only sees 88v.

This Photobucket is killing me!

Ok, thanks. That makes sense.

There's 120V at the fan motor capacitor. Does that negate what you said?

What you're saying is I should check the main voltage supply coming in, maybe clean the connectors, etc in the air handler in the house, or at the compressor. Or what the hell, both of them.

I'm not crazy about messing with them - those capacitors are nasty. I'll give it a go. Thanks again for the advice.

I tried jumping the R and G to get the fan going - that's how you manually test the fan right?

OK, further development - the fan won't cut on at all. Even when the compressor is off, and even when I jumper the R and G wires, it doesn't cut on. There is 121v at the fan motor capacitor.

There are 3 relay looking things in the wall of the cooling duct. Are these temperature sensors or something? The main current supply starts at one of them and moves to the next and next.

The relay, I checked the fuse - it's OK.

There is voltage at the capacitor so I'm thinking everything up to there (inc. relay) must be OK? I don't hear the relay click when I turn on the fan, but maybe it doesn't click, I don't know.

So, I guess I should check the motor windings, but there are 3 wires red, black, yellow. I can post a schematic if that could help. I'll get a picture and put it up in the next post.

Here's the best pic I could get of the air handler schematic

OK, you can't insert pics in this forum. Here it is at

http://www.pauldrayton.com/uploadfiles/pics/ACSymatic2-large.jpg

http://www.pauldrayton.com/uploadfiles/pics/ACSymatic-large.jpg


Where should I poke around now?

I need to see a photo showing the compressor and fan motor and it's voltage supplies. The lower left corner is probably what I need to see.

I'm still confident that the compressor and fan motor can be treated as black boxes, without measuring winding resistance or capacitor voltage.

When the compressor is on and the fan motor turns off by itself I need the voltage into the compressor and the voltage into the fan motor.

If they both go down when the compressor is on, I'd look for a bad connection at the location I described.

The default fix is to tighten all connections after turning off the breaker.

Be careful! Work slowly and deliberately.

If the 120v-N-120v going into your A/C measured at the A/C terminals drops to 90v-N-120v when the compressor starts, the problem is upstream of the A/C unit, probably in the breaker panel.

Thanks WDIBAA,

It's raining like a monkey here, so I'm on standby. But the rain did drop the temp to 69 so I'm cool with that!

By AC terminals, you mean the power going to the compressor? So measure each leg with the AC on? Do I have to do it just as it cuts on, or will it be low after say 30 seconds (if I have to test 2 of them) Or I could measure across both and see if the 240 drops to 220 or so?

HEre's a shot of the compressor schematic. A really big one for up close is here (http://www.pauldrayton.com/uploadfiles/pics/compressordiag003.jpg)

http://www.pauldrayton.com/uploadfiles/pics/compressordiag003-large.jpg

and I'll have to chew on it for a while.

By AC terminals, you mean the power going to the compressor?

No, the power going into the whole unit (fan, compressor, coils, etc.) while the compressor is on. Because, the problem may be upstream, like at the breaker panel.

I'm working from a schematic that I drew. You can always go from schematic to wiring diagram but not the other way round.

The one ohm bad connection on my schematic can be almost anywhere upstream of the fan/compressor; inside the unit or outside the unit or at the breaker panel.

So measure each leg with the AC on?

Yes.

Do I have to do it just as it cuts on,

Yes, try it a few seconds after the compressor starts.

or will it be low after say 30 seconds (if I have to test 2 of them) Or I could measure across both and see if the 240 drops to 220 or so?

If my assumptions are correct, the 240v will drop, maybe down to 210v. The drop will be across the same 120v supply that powers the fan, the other 120v should stay at 120v.

I thought I could write clearly until I got onto this Forum!

I'll be back.

Seems like the fan (CM) and the compressor (comp) both run on 240v, which is supplied by the box just to the left of the label "alternate double pole contactor."

L1 to T1 or L2 to T2 could be a high resistance connection. Since T2 is supplied by L2 through relay contacts, I'd suspect them first.
Closed relay contacts carrying rated current should have a drop of <30 millivolts. From your symptoms I'd say this drop is considerably higher.

But, if the L1/T1 and L2/T2 voltage drop is OK, then look at the voltage at L1 and L2. If L1 to N and L2 to N are not both 120v, look upstream toward the breaker panel for a high resistance connection.

If L1 to N and L2 to N are both 120v, and the L1/T1, etc., voltage drops are OK, then we have to go downstream and get into the details of this unit. We'll cross that bridge when we come to it.

I'm sure this unit has overload sensors, but, I don't know how many times you can safely start this unit with the fan not running before you damage it, so you want to be quick with taking these voltage readings. The tests you're running may not have been foreseen by the manu, so the safety sensors may be fooled.

THanks, that's pretty specific - I'll check those.

I just had a thought though - to be clear - by fan motor I mean the inside blower fan, not the compressor fan.

The compressor fan blows fine and the compressor comes on fine. It's the blower inside the house, the squirrel cage fan, air mover, that doesn't blow.

I hope I didn't use the wrong terminology and have you on a wild goose chase. :eek:

So, considering the above, do the checks you wrote in your previous post still apply?

Thanks

Pick wrong tree, bark up it.
No, don't go poking around the compressor.

The problem is definitely upstream of what you sent me, but you still need to look for a bad connection that is shared by the inside blower fan and the outside compressor. There can't be too many of them. And my 120v fan, 240v compressor theory is back in vogue. If I can get a photo uploaded, you'll see a schematic of what I mean.
This one should be simple.

Or, the logic circuitry controlling all this equipment might be commanding this to happen, for some unknown reason. This logic circuitry could be located in the thermostat, or elsewhere, or both places.
This one will be difficult.

WDIBAA, you're a real trooper! I can't tell you how much I appreciate your help.

There is 242 v coming into the blower assembly, so it seems the inside fan (I'll call it the blower from now on) is 240V.

I have put the old thermostat back on and the blower fan will not blow at any setting. Does that do any damage to the in vogue bad leg theory?

I'm pulling out the PCB that has the relay on it and see if it is allowing anything through.

The fan capacitor looks like it only gets 120V, is that how it should be? I can put up a better circuit diagram - one of the block diagram and one of the wiring if needed/wanted.

Paul.

more like Captain Ahab in Moby Dick.

There is 242 v coming into the blower assembly, so it seems the inside fan (I'll call it the blower from now on) is 240V.

I'd still look for a bad connection but my hopes are dimming.

I have put the old thermostat back on and the blower fan will not blow at any setting. Does that do any damage to the in vogue bad leg theory?

If the symptom changes for the worse with the old T-stat I'd say it has problems, too.

I'm pulling out the PCB that has the relay on it and see if it is allowing anything through.

I'd look upstream for more system-level problems like bad power connections and not down in the details

The fan capacitor looks like it only gets 120V, is that how it should be?

Don't know. If I suspect a cap (which I don't in this case) I check it out of circuit (see my previous posts).

I can put up a better circuit diagram - one of the block diagram and one of the wiring if needed/wanted.

You might try a system level diagram showing the inside fan as a box and the outside compressor as a box and the wiring that connects both of them to the main breaker panel.

Someday I'll tell my grandchildren about this excellent adventure in Cyberspace.

Paul.

My first name is WDI, as in "Why Do I Bother At All"?, but ? is not allowed in usernames.

Well, yes, we're having a whale of a time...

Developments,

I jumped the fan to the mains coming in and it blows fine.

I checked the power coming in all the way to the relay, it is fine - one leg coming in at 121V. So it's all fine up to the relay (I assume that since there is power through all the components up to it), and then if I bypass the relay and jump the fan directly, it works.

To me that says bad relay, right? It has power and doesn't click when there is power put to it (there is 121v going to it. )

It's shown in the first picture I posted, in the middle on the left - FR in the PCB box. It has 2 black wires coming in. They have 121V. The blue has 120V too. However, SPT (the line to the fan wiring) doesn't get any voltage.

As I understand it, when the relay gets power through NC (the blue wire) it should allow the power through from the right to the left through the black wire and start the fan.

I'm used to a relay having 4 connectors, so maybe I'm reading it wrong.

If I'm not reading it wrong, then it's the relay right?

THe only thing bugging me is there was a smell of burning when I jumped the fan. Is there any common explanation of that? I didn't see or smell any smoke. It was the smell of the AC heater working.

SO, whatcha think captain?

EDIT: Weird thing is there is 120 v at both blue and black lines of the relay. I'm confused...

I think the white whale is ramming us and we are sinking fast,
but if your name were Ishmael you wouldn't have anything to worry about, if you get my drift.

In the name of [pick your Deity] don't go doing any more jumper wires!
Electrical stuff, even those things with coils in them, don't like to be provoked, and they will pay you back (immediately or later).

If we fix this, we're heroes. If we fail, we're fools.

Sinking or not, I have to sleep on this. . .

You guys have been batting this thing back and forth.

I originally thought indoor fan and got confused with out door diagram.

Post #11 helped.

WDIBAA heat pump will always be 220 in and out unless duel fuel usually has 120 in.

Problem #1: Indoor fan shutting off when compressor turns on.
Additional info: Fan runs when compressor turns off.

Problem #2: Wife not happy living in sauna.
Additional info: Mad wife, Bad VEERRY Bad.

When troubleshooting, keep it simple. In this system each unit RUNS on 220. Without 220 to the outdoor unit the stat can open and close the contactor all day, nothing will happen if there is no 220 there.

With the indoor no 220 also means no 24v control power.

Since both the indoor and outdoor run the problem is not with line (220) voltage.

This leaves the 24v control circuit. Is the fan in "on" or "Auto"? Just wondering why the fan runs with compressor off.

Assuming the stat has a common wire, and troubleshooting at the stat, heres is what should be seen. With system off, there should be 24v between R and C. R is 24v hot, C is common and usually grounded at the transformer.

That said, with the system off and trusty multimeter at stat or control board/terminal block is airhandler, you would read 24v between R and C, G, Y, O, W. Because the circuit os open and your reading from hot (R) and common through the various coils of relays and contactors.

So remembering to two legs, if the compressor were running in cooling, at the stat R to O and R to Y would read ZERO volts as the circuit is closed, C to Y or O would read 24 becuase your actually reading C to R because R is closed to both Y and O.

That's the compressor and reversing valve, which isn't the problem. The real problem is the MAD wife which is caused (at this point) by the indoor blower problem.

With system in cool and fan in auto, compressor running and no indoor fan, what is the voltage between R and G? 24 volts means the stat relay is not closed, 0 means it is closed. Zero also means the stat is sending the signal to the indoor unit to run the fan.

24 volts means we have a stat problem, 0 indicates an airhaldler problem. Meaning we are telling the fan to run but , of course, it isn't.

Shift all troubleshooting to the airhandler. What's in there? Is it a simple relay or a circuit board?

Bat that around for a while and post results.

Make, Model, Serial numbers may help.

OK, here's the scoop, JarredsDad.

BTW, the fan doesn't run at all now. It was running with the compressor off for a little while, but won't run at all now.

Thanks for the info. Helped make sense of things.

There is 24vac at R to all the others you mentioned.

But I don't see how to see what voltage is at R to Y when the fan is on, with the thermostat attached.

Anyway, an electrician friend of mine just came round and said it's more than likely the PCB with the relay. Either the relay itself, or the circuit board. Makes sense to me - there is 24v going to the circuit board, but the relay doesn't switch. Actually, the voltmeter reads 28VAC, but I assume that's OK.

So I'm going to get a new PCB and put it in. I don't see what else it could be, there are only 3 other switch looking things on the vent walls, and there is current downstream from them, so they're not the problem.

I'll let you know what happens, maybe some other poor sailor can avoid the pain...

It's a PAYNE PF1MNB042

I have the fan jumped and the compressor on. Sparky friend had a look and said it's OK. Main problem is handled - wife not so hot any more, well temperature wise I mean.

The other problem of the fan not working properly can be handled later. ...

Thank God for EM's (EN here).

The purpose of my sugestion to check R and Y was an exersise to ensure you knew what you were doing.

Follow the voltage until it stops, before it is supposed to.

What I wanted to get through in that post was basic t-shooting. Follow the signal. If the the fan zero volts R to G, or 24v between G and C, then the stat is telling the fan to run. If you have either of the 2 then the stat is doing it's job. Next thing to look at is the Airhandler.

Which Sparky did apparently find, and you now have a clue. If the board is being told to run the fan and it is not, bad board.

Electricians Mates, where would the Navy be without them?

BZ to you and Double BZ to your Sparky buddy.

OK, I'm abviously out of my depth here.

What is an EM, and what is an EN?

ANd what is a BZ?

My electrician friend is not called Sparky, it's a slang term for an electrician, british I believe.

I'm thinking of buying just the relay and sautering it in. The board is $90. Cheaper than a AC guy I guess. The one AC person I called wanted $150 to install a service port that costs $7 for the valve and took me 5 minutes to put in. So I shudder to think what I have saved already. I think I can treat myself to another bottle of 40 Barrel whiskey.

I wondered what was keeping you. . .

I'm trying to order this relay board from the manufacturer and they want my AC license...grrrrr.

I've got the fan jumped and the thing is working, so the wife is not mad, but now I am becuase of indiscriminate bureaucratic laws.....

If you're sure it's the relay:

-Google the numbers off the relay case,
-get the coil and contact ratings from the relay OEM off the Internet
-pick an electrical and possibly mechanical equivalent from Digi-key or Hosfelt.com,
-solder it in with a low-wattage soldering iron.

Thanks BAA. It was hard to find - they don't make the same thing anymore.

But I was able to find the whole circuit board for $36, available locally. A friend is going to phone in his AC licence and I'll go pick it up.

Good, 'cause I forgot to mention that the voltage spike suppressor for the relay coil is sometimes in the relay and sometimes not, and electrically equivalent relays may not have it.